22 files changed, 1855 insertions, 0 deletions

diff --git a/src/scene/animation.c b/src/scene/animation.c
new file mode 100644
index 0000000..08d02ce
--- /dev/null
+++ b/src/scene/animation.c
@@ -0,0 +1,524 @@
+#include "animation_impl.h"
+
+#include "node_impl.h"
+#include "scene_memory.h"
+
+#include <string.h>
+
+// #include <log/log.h> // Debugging.
+
+static const R PLAYBACK_UNINITIALIZED = -1;
+
+static joint_idx get_anima_root_joint_index(Anima* anima) {
+  assert(anima);
+  assert(anima->num_joints > 0);
+  assert(anima->num_joints < GFX_MAX_NUM_JOINTS);
+  return anima->num_joints - 1;
+}
+
+static Joint* get_anima_root_joint(Anima* anima) {
+  assert(anima);
+  return &anima->joints[get_anima_root_joint_index(anima)];
+}
+
+static const Joint* get_anima_joint(const Anima* anima, joint_idx index) {
+  assert(anima);
+  assert(index < GFX_MAX_NUM_JOINTS);
+  assert(index != INDEX_NONE);
+  assert(index < anima->num_joints);
+  return &anima->joints[index];
+}
+
+static Joint* get_anima_joint_mut(Anima* anima, joint_idx index) {
+  return (Joint*)get_anima_joint(anima, index);
+}
+
+static const Joint* get_skeleton_joint(
+    const Anima* anima, const Skeleton* skeleton, joint_idx index) {
+  assert(anima);
+  assert(skeleton);
+  return get_anima_joint(anima, skeleton->joints[index]);
+}
+
+static void set_joint_parent(
+    Anima* anima, joint_idx joint_index, joint_idx parent_index) {
+  assert(anima);
+  assert(joint_index != INDEX_NONE);
+  assert(joint_index != get_anima_root_joint_index(anima));
+  assert(parent_index != INDEX_NONE);
+
+  Joint* parent = get_anima_joint_mut(anima, parent_index);
+
+  if (parent->child == INDEX_NONE) {
+    parent->child = joint_index;
+  } else {
+    // Find the last child in the chain of children.
+    Joint* child = get_anima_joint_mut(anima, parent->child);
+    while (child->next != INDEX_NONE) {
+      child = get_anima_joint_mut(anima, child->next);
+    }
+    // Wire up this joint as the last child's sibling.
+    child->next = joint_index;
+  }
+}
+
+static void make_joint(Anima* anima, const JointDesc* desc, Joint* joint) {
+  assert(anima);
+  assert(desc);
+  assert(joint);
+
+  // The joint matrix needs to be initialized so that meshes look right even if
+  // no animation is played. Initializing joint matrices to the identity makes
+  // meshes appear in their bind pose.
+  joint->child           = INDEX_NONE;
+  joint->next            = INDEX_NONE;
+  joint->transform       = mat4_id();
+  joint->inv_bind_matrix = desc->inv_bind_matrix;
+  joint->joint_matrix    = mat4_id();
+  joint->box             = desc->box;
+}
+
+static Skeleton* make_skeleton(const SkeletonDesc* desc) {
+  assert(desc);
+  assert(desc->num_joints <= GFX_MAX_NUM_JOINTS);
+
+  Skeleton* skeleton   = mem_alloc_skeleton();
+  skeleton->num_joints = desc->num_joints;
+  memcpy(
+      skeleton->joints, desc->joints,
+      desc->num_joints * sizeof(skeleton->joints[0]));
+  return skeleton;
+}
+
+static Animation* make_animation(const AnimationDesc* desc) {
+  assert(desc);
+  assert(desc->num_channels < GFX_MAX_NUM_CHANNELS);
+
+  Animation* animation    = mem_alloc_animation();
+  animation->name         = desc->name;
+  animation->duration     = 0;
+  animation->num_channels = desc->num_channels;
+  R start_time            = 0;
+  R end_time              = 0;
+
+  for (size_t c = 0; c < desc->num_channels; ++c) {
+    const ChannelDesc* channel_desc = &desc->channels[c];
+    Channel*           channel      = &animation->channels[c];
+
+    channel->target        = channel_desc->target;
+    channel->type          = channel_desc->type;
+    channel->interpolation = channel_desc->interpolation;
+    channel->num_keyframes = channel_desc->num_keyframes;
+    assert(channel_desc->num_keyframes < GFX_MAX_NUM_KEYFRAMES);
+
+    for (size_t k = 0; k < channel_desc->num_keyframes; ++k) {
+      const KeyframeDesc* keyframe_desc = &channel_desc->keyframes[k];
+      Keyframe*           keyframe      = &channel->keyframes[k];
+
+      keyframe->time        = keyframe_desc->time;
+      keyframe->translation = keyframe_desc->translation;
+      keyframe->rotation    = keyframe_desc->rotation;
+
+      start_time = keyframe->time < start_time ? keyframe->time : start_time;
+      end_time   = keyframe->time > end_time ? keyframe->time : end_time;
+    }
+  }
+
+  // LOGD("Animation start/end: %f / %f", start_time, end_time);
+  animation->duration = end_time - start_time;
+  assert(animation->duration >= 0);
+  return animation;
+}
+
+Anima* gfx_make_anima(const AnimaDesc* desc) {
+  assert(desc);
+  assert(desc->num_joints > 0);
+  assert(desc->num_joints <= GFX_MAX_NUM_JOINTS);
+  // All joints should have a parent except for the root.
+  for (size_t i = 0; i < desc->num_joints - 1; ++i) {
+    const joint_idx parent = desc->joints[i].parent;
+    assert(parent != INDEX_NONE);
+    assert(parent < desc->num_joints);
+  }
+  // The root should have no parent.
+  assert(desc->joints[desc->num_joints - 1].parent == INDEX_NONE);
+
+  Anima* anima = mem_alloc_anima();
+
+  // Wire the skeletons in the same order they are given in the descriptor.
+  Skeleton* last_skeleton = 0;
+  for (size_t i = 0; i < desc->num_skeletons; ++i) {
+    Skeleton*          skeleton       = make_skeleton(&desc->skeletons[i]);
+    const skeleton_idx skeleton_index = mem_get_skeleton_index(skeleton);
+    if (last_skeleton == 0) {
+      anima->skeleton = skeleton_index;
+    } else {
+      last_skeleton->next = skeleton_index;
+    }
+    last_skeleton = skeleton;
+  }
+
+  // Wire the animations in the same order they are given in the descriptor.
+  Animation* last_animation = 0;
+  for (size_t i = 0; i < desc->num_animations; ++i) {
+    Animation*          animation       = make_animation(&desc->animations[i]);
+    const animation_idx animation_index = mem_get_animation_index(animation);
+    if (last_animation == 0) {
+      anima->animation = animation_index;
+    } else {
+      last_animation->next = animation_index;
+    }
+    last_animation = animation;
+  }
+
+  // Create joints.
+  anima->num_joints = desc->num_joints;
+  // Initialize all joints.
+  // Child and sibling pointers must be initialized before wiring up the
+  // hierarchy.
+  for (size_t i = 0; i < desc->num_joints; ++i) {
+    Joint* joint = get_anima_joint_mut(anima, i);
+    make_joint(anima, &desc->joints[i], joint);
+  }
+  // Wire up joints to their parents. -1 to skip the root.
+  for (size_t i = 0; i < desc->num_joints - 1; ++i) {
+    set_joint_parent(anima, i, desc->joints[i].parent);
+  }
+
+  return anima;
+}
+
+void gfx_destroy_anima(Anima** anima) {
+  assert(anima);
+
+  if (*anima) {
+    for (skeleton_idx i = (*anima)->skeleton; i.val != 0;) {
+      Skeleton* skeleton = mem_get_skeleton(i);
+      i                  = skeleton->next;
+      mem_free_skeleton(&skeleton);
+    }
+
+    for (animation_idx i = (*anima)->animation; i.val != 0;) {
+      Animation* animation = mem_get_animation(i);
+      i                    = animation->next;
+      mem_free_animation(&animation);
+    }
+
+    if ((*anima)->parent.val) {
+      gfx_del_node((*anima)->parent);
+    }
+
+    mem_free_anima(anima);
+  }
+}
+
+static Animation* find_animation(animation_idx index, const char* name) {
+  assert(name);
+
+  while (index.val != 0) {
+    Animation* animation = mem_get_animation(index);
+    if (sstring_eq_cstr(animation->name, name)) {
+      // LOGD(
+      //     "Found animation at index %u, %s - %s", index.val,
+      //     sstring_cstr(&animation->name), name);
+      // LOGD("Animation has duration %f", animation->duration);
+      return animation;
+    }
+    index = animation->next;
+  }
+
+  return 0;
+}
+
+bool gfx_play_animation(Anima* anima, const AnimationPlaySettings* settings) {
+  assert(anima);
+  assert(settings);
+
+  // TODO: Should we animate at t=0 here to kickstart the animation? Otherwise
+  //  the client is forced to call gfx_update_animation() to do this.
+  Animation* animation = find_animation(anima->animation, settings->name);
+  if (!animation) {
+    return false;
+  }
+  // Playback initialized on first call to update().
+  AnimationState* state = &anima->state;
+  state->start_time     = PLAYBACK_UNINITIALIZED;
+  state->animation      = mem_get_animation_index(animation);
+  state->loop           = settings->loop;
+  return true;
+}
+
+static void gfx_set_joint_position(Joint* joint, vec3 position) {
+  assert(joint);
+  mat4_set_v3(&joint->transform, position);
+}
+
+static void gfx_set_joint_rotation(Joint* joint, quat rotation) {
+  assert(joint);
+  mat4_set_3x3(&joint->transform, mat4_from_quat(rotation));
+}
+
+static void find_keyframes(const Channel* channel, R t, int* prev, int* next) {
+  assert(channel);
+  assert(prev);
+  assert(next);
+
+  *prev = -1;
+  *next = 0;
+  while (((*next + 1) < (int)channel->num_keyframes) &&
+         (t >= channel->keyframes[*next + 1].time)) {
+    (*prev)++;
+    (*next)++;
+  }
+}
+
+static R normalize_time(R a, R b, R t) {
+  assert(a <= t);
+  assert(t <= b);
+  return (t - a) / (b - a);
+}
+
+static quat interpolate_rotation(
+    const Channel* channel, int prev, int next, R t) {
+  assert(channel);
+
+  if (next == 0) {
+    // Animation has not started at this point in time yet.
+    return channel->keyframes[next].rotation;
+  } else {
+    switch (channel->interpolation) {
+    case StepInterpolation:
+      return channel->keyframes[prev].rotation;
+    case LinearInterpolation: {
+      const R normalized_t = normalize_time(
+          channel->keyframes[prev].time, channel->keyframes[next].time, t);
+      return qnormalize(qslerp(
+          channel->keyframes[prev].rotation, channel->keyframes[next].rotation,
+          normalized_t));
+      break;
+    }
+    case CubicSplineInterpolation:
+      assert(false); // TODO
+      return qmake(0, 0, 0, 0);
+    default:
+      assert(false);
+      return qmake(0, 0, 0, 0);
+    }
+  }
+}
+
+static vec3 interpolate_translation(
+    const Channel* channel, int prev, int next, R t) {
+  assert(channel);
+
+  if (next == 0) {
+    // Animation has not started at this point in time yet.
+    return channel->keyframes[next].translation;
+  } else {
+    switch (channel->interpolation) {
+    case StepInterpolation:
+      return channel->keyframes[prev].translation;
+    case LinearInterpolation: {
+      const R normalized_t = normalize_time(
+          channel->keyframes[prev].time, channel->keyframes[next].time, t);
+      return vec3_lerp(
+          channel->keyframes[prev].translation,
+          channel->keyframes[next].translation, normalized_t);
+      break;
+    }
+    case CubicSplineInterpolation:
+      assert(false); // TODO
+      return vec3_make(0, 0, 0);
+    default:
+      assert(false);
+      return vec3_make(0, 0, 0);
+    }
+  }
+}
+
+static void animate_channel(Anima* anima, const Channel* channel, R t) {
+  assert(anima);
+  assert(channel);
+  assert(channel->target < anima->num_joints);
+
+  int prev, next;
+  find_keyframes(channel, t, &prev, &next);
+
+  // Note that not all channels extend to the duration of an animation; some
+  // channels may stop animating their targets earlier. Clamp the animation time
+  // to the channel's end keyframe to make the rest of the math (normalize_time)
+  // work.
+  t = t > channel->keyframes[next].time ? channel->keyframes[next].time : t;
+
+  Joint* target = get_anima_joint_mut(anima, channel->target);
+
+  switch (channel->type) {
+  case RotationChannel: {
+    const quat rotation = interpolate_rotation(channel, prev, next, t);
+    gfx_set_joint_rotation(target, rotation);
+    break;
+  }
+  case TranslationChannel: {
+    const vec3 translation = interpolate_translation(channel, prev, next, t);
+    gfx_set_joint_position(target, translation);
+    break;
+  }
+  // Not yet supported.
+  case ScaleChannel:
+  case WeightsChannel:
+  default:
+    // TODO: Add back the assertion or add support for scaling.
+    // assert(false);
+    break;
+  }
+}
+
+static void compute_joint_matrices_rec(
+    Anima* anima, Joint* joint, const mat4* parent_global_joint_transform,
+    const mat4* root_inv_global_transform) {
+  assert(anima);
+  assert(joint);
+  assert(parent_global_joint_transform);
+  assert(root_inv_global_transform);
+
+  const mat4 global_joint_transform =
+      mat4_mul(*parent_global_joint_transform, joint->transform);
+
+  // Compute this joint's matrix.
+  joint->joint_matrix = mat4_mul(
+      *root_inv_global_transform,
+      mat4_mul(global_joint_transform, joint->inv_bind_matrix));
+
+  // Recursively compute the joint matrices for this joint's siblings.
+  if (joint->next != INDEX_NONE) {
+    Joint* sibling = get_anima_joint_mut(anima, joint->next);
+
+    compute_joint_matrices_rec(
+        anima, sibling, parent_global_joint_transform,
+        root_inv_global_transform);
+  }
+
+  // Recursively compute the joint matrices for this joint's children.
+  if (joint->child != INDEX_NONE) {
+    Joint* child = get_anima_joint_mut(anima, joint->child);
+
+    compute_joint_matrices_rec(
+        anima, child, &global_joint_transform, root_inv_global_transform);
+  }
+}
+
+void gfx_update_animation(Anima* anima, R t) {
+  assert(anima);
+
+  AnimationState* state = &anima->state;
+  if (state->animation.val == 0) {
+    return; // No active animation.
+  }
+  const Animation* animation = mem_get_animation(state->animation);
+  assert(animation);
+
+  // On a call to play(), the start time is set to -1 to signal that the
+  // animation playback has not yet been initialized.
+  if (state->start_time == PLAYBACK_UNINITIALIZED) {
+    state->start_time = t;
+  }
+  // Locate the current time point inside the animation's timeline.
+  assert(t >= state->start_time);
+  assert(animation->duration >= 0.0);
+  const R local_time     = t - state->start_time;
+  const R animation_time = state->loop
+                               ? rmod(local_time, animation->duration)
+                               : clamp(local_time, 0.0, animation->duration);
+
+  // LOGD(
+  //     "animation_time = %f, animation duration: %f", animation_time,
+  //     animation->duration);
+
+  // Play through the animation to transform skeleton nodes.
+  for (size_t i = 0; i < animation->num_channels; ++i) {
+    const Channel* channel = &animation->channels[i];
+    animate_channel(anima, channel, animation_time);
+  }
+
+  // Compute joint matrices after having transformed the skeletons.
+  //
+  // The anima's parent node is the common ancestor of all skeletons, and its
+  // transform maps the skeletons from object space to world space. This is the
+  // transform used as the "global transform" in the joint matrix equations.
+  //
+  // Joint matrix calculation begins by descending from the anima's root joint,
+  // which we have constructed to be the common root of all skeletons.
+  //
+  // This procedure touches every joint exactly once.
+  SceneNode* root_node = mem_get_node(anima->parent);
+  // LOGD("Root: %u, child: %u", anima->parent.val, root->child.val);
+  const mat4 root_global_transform = gfx_get_node_global_transform(root_node);
+  const mat4 root_inv_global_transform = mat4_inverse(root_global_transform);
+
+  Joint* root_joint = get_anima_root_joint(anima);
+  compute_joint_matrices_rec(
+      anima, root_joint, &root_global_transform, &root_inv_global_transform);
+}
+
+const Skeleton* gfx_get_anima_skeleton(const Anima* anima, size_t i) {
+  assert(anima);
+
+  skeleton_idx    skeleton_index = anima->skeleton;
+  const Skeleton* skeleton       = mem_get_skeleton(skeleton_index);
+
+  for (size_t j = 1; j < i; ++j) {
+    skeleton_index = skeleton->next;
+    mem_get_skeleton(skeleton_index);
+  }
+
+  return skeleton;
+}
+
+size_t gfx_get_skeleton_num_joints(const Skeleton* skeleton) {
+  assert(skeleton);
+  return skeleton->num_joints;
+}
+
+bool gfx_joint_has_box(
+    const Anima* anima, const Skeleton* skeleton, size_t joint_index) {
+  assert(anima);
+  assert(skeleton);
+  assert(joint_index < skeleton->num_joints);
+
+  const Joint* joint = get_skeleton_joint(anima, skeleton, joint_index);
+  return !aabb3_is_empty(joint->box);
+}
+
+Box gfx_get_joint_box(
+    const Anima* anima, const Skeleton* skeleton, size_t joint_index) {
+  assert(anima);
+  assert(skeleton);
+
+  const Joint* joint = get_skeleton_joint(anima, skeleton, joint_index);
+
+  // Transform the box to anima space.
+  // Note that joint matrices do not usually have a translation since joints
+  // mostly just rotate with respect to their parent.
+  const vec3 pmin = joint->box.min;
+  const vec3 pmax = joint->box.max;
+  return (Box){
+      .vertices = {
+                   mat4_mul_vec3(
+                   joint->joint_matrix, vec3_make(pmin.x, pmin.y, pmax.z), 1),
+                   mat4_mul_vec3(
+                   joint->joint_matrix, vec3_make(pmax.x, pmin.y, pmax.z), 1),
+                   mat4_mul_vec3(
+                   joint->joint_matrix, vec3_make(pmax.x, pmax.y, pmax.z), 1),
+                   mat4_mul_vec3(
+                   joint->joint_matrix, vec3_make(pmin.x, pmax.y, pmax.z), 1),
+                   mat4_mul_vec3(
+                   joint->joint_matrix, vec3_make(pmin.x, pmin.y, pmin.z), 1),
+                   mat4_mul_vec3(
+                   joint->joint_matrix, vec3_make(pmax.x, pmin.y, pmin.z), 1),
+                   mat4_mul_vec3(
+                   joint->joint_matrix, vec3_make(pmax.x, pmax.y, pmin.z), 1),
+                   mat4_mul_vec3(
+                   joint->joint_matrix, vec3_make(pmin.x, pmax.y, pmin.z), 1),
+                   }
+  };
+}
diff --git a/src/scene/animation_impl.h b/src/scene/animation_impl.h
new file mode 100644
index 0000000..4408158
--- /dev/null
+++ b/src/scene/animation_impl.h
@@ -0,0 +1,98 @@
+#pragma once
+
+#include <gfx/scene/animation.h>
+#include <gfx/sizes.h>
+
+#include "types.h"
+
+#include <cstring.h>
+#include <math/defs.h>
+#include <math/mat4.h>
+#include <math/quat.h>
+#include <math/vec3.h>
+
+#include <stddef.h>
+#include <stdint.h>
+
+typedef struct Buffer Buffer;
+
+// Currently ignoring scale in skinning and animation.
+//
+// TODO: Simultaneous animation of disjoint animations.
+
+/// Skeleton joint.
+/// Joints are mutable and store the transform and joint matrices that result
+/// from animation, aside from the inverse bind matrix.
+typedef struct Joint {
+  joint_idx child;       /// First child Joint; index into Anima's joints.
+  joint_idx next;        /// Next sibling Joint; index into Anima's joints.
+  mat4      transform;   /// Local transform relative to parent.
+  mat4  inv_bind_matrix; /// Transforms the mesh into the joint's local space.
+  mat4  joint_matrix;    /// inv(global) * global joint transform * inv(bind).
+  aabb3 box;             /// Bounding box of vertices affected by joint.
+} Joint;
+
+/// Animation skeleton.
+typedef struct Skeleton {
+  skeleton_idx next;
+  size_t       num_joints;
+  joint_idx joints[GFX_MAX_NUM_JOINTS]; /// Indices into Anima's joints array.
+} Skeleton;
+
+/// A keyframe of animation.
+typedef struct Keyframe {
+  R time; /// Start time in [0, end animation time]
+  union {
+    vec3 translation;
+    quat rotation;
+  };
+} Keyframe;
+
+/// Animation channel.
+typedef struct Channel {
+  joint_idx              target; /// Index into Anima's joints array.
+  ChannelType            type;
+  AnimationInterpolation interpolation;
+  size_t                 num_keyframes;
+  Keyframe               keyframes[GFX_MAX_NUM_KEYFRAMES];
+} Channel;
+
+/// A skeletal animation.
+typedef struct Animation {
+  animation_idx next;
+  sstring       name;
+  R             duration;
+  size_t        num_channels;
+  Channel       channels[GFX_MAX_NUM_CHANNELS];
+} Animation;
+
+/// Animation state.
+///
+/// This represents the current state of an animation.
+typedef struct AnimationState {
+  R start_time; // Time when the current animation started playing. -1 means the
+                // animation playback has not yet been initialized.
+  animation_idx animation; // Current animation. 0 = no animation.
+  bool          loop;
+} AnimationState;
+
+/// Animation object.
+///
+/// This is the top-level animation object that encapsulates everything
+/// necessary for animation.
+///
+/// For lack of a better name, this is called an Anima. It is short and the
+/// Latin root of animation.
+///
+/// The last joint of the joints array at index 'num_joints - 1' is the root of
+/// all skeletons; specifically, the root of all joints that otherwise would
+/// have no parent (a skeleton need not have its own root and can be a set of
+/// disjoint node hierarchies).
+typedef struct Anima {
+  node_idx       parent;     /// Parent SceneNode.
+  skeleton_idx   skeleton;   /// Index of first skeleton.
+  animation_idx  animation;  /// Index of first animation.
+  AnimationState state;      /// Current animation state.
+  size_t         num_joints; /// Number of actual joints in the array.
+  Joint          joints[GFX_MAX_NUM_JOINTS]; /// Shared by all skeletons.
+} Anima;
diff --git a/src/scene/camera.c b/src/scene/camera.c
new file mode 100644
index 0000000..be7d806
--- /dev/null
+++ b/src/scene/camera.c
@@ -0,0 +1,37 @@
+#include "camera_impl.h"
+
+#include "node_impl.h"
+#include "scene_memory.h"
+
+#include <assert.h>
+
+SceneCamera* gfx_make_camera() {
+  SceneCamera* camera = mem_alloc_camera();
+
+  camera->camera = camera_perspective(
+      /*fovy=*/90.0 * TO_RAD, /*aspect=*/16.0 / 9.0,
+      /*near=*/0.1, /*far=*/1000);
+
+  return camera;
+}
+
+void gfx_destroy_camera(SceneCamera** camera) {
+  assert(camera);
+  if (*camera) {
+    if ((*camera)->parent.val) {
+      gfx_del_node((*camera)->parent);
+    }
+    mem_free_camera(camera);
+  }
+}
+
+void gfx_set_camera_camera(SceneCamera* scene_camera, Camera* camera) {
+  assert(scene_camera);
+  assert(camera);
+  scene_camera->camera = *camera;
+}
+
+Camera* gfx_get_camera_camera(SceneCamera* camera) {
+  assert(camera);
+  return &camera->camera;
+}
diff --git a/src/scene/camera_impl.h b/src/scene/camera_impl.h
new file mode 100644
index 0000000..20c3890
--- /dev/null
+++ b/src/scene/camera_impl.h
@@ -0,0 +1,12 @@
+#pragma once
+
+#include <gfx/scene/camera.h>
+
+#include "types.h"
+
+#include <math/camera.h>
+
+typedef struct SceneCamera {
+  Camera camera;
+  node_idx parent; // Parent SceneNode.
+} SceneCamera;
diff --git a/src/scene/light.c b/src/scene/light.c
new file mode 100644
index 0000000..adbec8d
--- /dev/null
+++ b/src/scene/light.c
@@ -0,0 +1,42 @@
+#include "light_impl.h"
+
+#include "node_impl.h"
+#include "scene_memory.h"
+
+#include <error.h>
+
+static void make_environment_light(
+    Light* light, const EnvironmentLightDesc* desc) {
+  assert(light);
+  assert(desc);
+  light->type                        = EnvironmentLightType;
+  light->environment.environment_map = desc->environment_map;
+}
+
+Light* gfx_make_light(const LightDesc* desc) {
+  assert(desc);
+
+  Light* light = mem_alloc_light();
+
+  switch (desc->type) {
+  case EnvironmentLightType:
+    make_environment_light(light, &desc->light.environment);
+    break;
+  default:
+    log_error("Unhandled light type");
+    gfx_destroy_light(&light);
+    return 0;
+  }
+
+  return light;
+}
+
+void gfx_destroy_light(Light** light) {
+  assert(light);
+  if (*light) {
+    if ((*light)->parent.val) {
+      gfx_del_node((*light)->parent);
+    }
+    mem_free_light(light);
+  }
+}
diff --git a/src/scene/light_impl.h b/src/scene/light_impl.h
new file mode 100644
index 0000000..1aa0bb4
--- /dev/null
+++ b/src/scene/light_impl.h
@@ -0,0 +1,25 @@
+#pragma once
+
+#include <gfx/scene/light.h>
+
+#include "types.h"
+
+typedef struct Texture Texture;
+
+/// An environment light.
+typedef struct EnvironmentLight {
+  const Texture* environment_map;
+  const Texture* irradiance_map;              // Renderer implementation.
+  const Texture* prefiltered_environment_map; // Renderer implementation.
+  int max_reflection_lod; // Mandatory when prefiltered_environment_map is
+                          // given.
+} EnvironmentLight;
+
+/// A scene light.
+typedef struct Light {
+  LightType type;
+  union {
+    EnvironmentLight environment;
+  };
+  node_idx parent; // Parent SceneNode.
+} Light;
diff --git a/src/scene/material.c b/src/scene/material.c
new file mode 100644
index 0000000..3248243
--- /dev/null
+++ b/src/scene/material.c
@@ -0,0 +1,57 @@
+#include "material_impl.h"
+
+#include "scene_memory.h"
+
+#include <gfx/core.h>
+
+static void material_make(Material* material, const MaterialDesc* desc) {
+  assert(material);
+  assert(desc);
+  assert(desc->num_uniforms < GFX_MAX_UNIFORMS_PER_MATERIAL);
+  material->num_uniforms = desc->num_uniforms;
+  for (int i = 0; i < desc->num_uniforms; ++i) {
+    material->uniforms[i] = desc->uniforms[i];
+  }
+}
+
+Material* gfx_make_material(const MaterialDesc* desc) {
+  assert(desc);
+  Material* material = mem_alloc_material();
+  material_make(material, desc);
+  return material;
+}
+
+void gfx_destroy_material(Material** material) { mem_free_material(material); }
+
+static void set_uniform(ShaderProgram* prog, const ShaderUniform* uniform) {
+  switch (uniform->type) {
+  case UniformTexture:
+    gfx_set_texture_uniform(prog, uniform->name.str, uniform->value.texture);
+    break;
+  case UniformMat4:
+    gfx_set_mat4_uniform(prog, uniform->name.str, &uniform->value.mat4);
+    break;
+  case UniformVec3:
+    gfx_set_vec3_uniform(prog, uniform->name.str, uniform->value.vec3);
+    break;
+  case UniformVec4:
+    gfx_set_vec4_uniform(prog, uniform->name.str, uniform->value.vec4);
+    break;
+  case UniformFloat:
+    gfx_set_float_uniform(prog, uniform->name.str, uniform->value.scalar);
+    break;
+  case UniformMat4Array:
+    gfx_set_mat4_array_uniform(
+        prog, uniform->name.str, uniform->value.array.values,
+        uniform->value.array.count);
+    break;
+  }
+}
+
+void material_activate(ShaderProgram* shader, const Material* material) {
+  assert(material);
+  for (int i = 0; i < material->num_uniforms; ++i) {
+    const ShaderUniform* uniform = &material->uniforms[i];
+    set_uniform(shader, uniform);
+  }
+}
diff --git a/src/scene/material_impl.h b/src/scene/material_impl.h
new file mode 100644
index 0000000..a6aa95b
--- /dev/null
+++ b/src/scene/material_impl.h
@@ -0,0 +1,16 @@
+#pragma once
+
+#include <gfx/scene/material.h>
+
+typedef struct ShaderProgram ShaderProgram;
+
+typedef struct Material {
+  ShaderUniform uniforms[GFX_MAX_UNIFORMS_PER_MATERIAL];
+  int           num_uniforms;
+} Material;
+
+/// Activate the material.
+///
+/// This activates the material's shader and configures the shader uniforms that
+/// are specific to the material.
+void material_activate(ShaderProgram* shader, const Material* material);
diff --git a/src/scene/mesh.c b/src/scene/mesh.c
new file mode 100644
index 0000000..1a93bed
--- /dev/null
+++ b/src/scene/mesh.c
@@ -0,0 +1,24 @@
+#include "mesh_impl.h"
+
+#include "scene_memory.h"
+
+#include <assert.h>
+
+static void mesh_make(Mesh* mesh, const MeshDesc* desc) {
+  assert(mesh);
+  assert(desc);
+  assert(desc->geometry);
+  assert(desc->material);
+  assert(desc->shader);
+  mesh->geometry = desc->geometry;
+  mesh->material = desc->material;
+  mesh->shader   = desc->shader;
+}
+
+Mesh* gfx_make_mesh(const MeshDesc* desc) {
+  Mesh* mesh = mem_alloc_mesh();
+  mesh_make(mesh, desc);
+  return mesh;
+}
+
+void gfx_destroy_mesh(Mesh** mesh) { mem_free_mesh(mesh); }
diff --git a/src/scene/mesh_impl.h b/src/scene/mesh_impl.h
new file mode 100644
index 0000000..560b77e
--- /dev/null
+++ b/src/scene/mesh_impl.h
@@ -0,0 +1,12 @@
+#pragma once
+
+#include <gfx/scene/mesh.h>
+
+typedef struct Mesh {
+  const Geometry* geometry;
+  const Material* material;
+  ShaderProgram*  shader;
+} Mesh;
+
+// TODO: a mesh_render() that takes a transform, applies the material and the
+// transform, and then renders the geometry.
diff --git a/src/scene/model.c b/src/scene/model.c
new file mode 100644
index 0000000..cc41a9a
--- /dev/null
+++ b/src/scene/model.c
@@ -0,0 +1,45 @@
+#include "model_impl.h"
+
+#include <gfx/scene/node.h>
+
+#include "scene_memory.h"
+
+#include <assert.h>
+
+Model* gfx_make_model(const SceneNode* root) {
+  assert(root);
+
+  Model* model = mem_alloc_model();
+  model->root  = mem_get_node_index(root);
+  return model;
+}
+
+void gfx_del_model(Model** model) {
+  assert(model);
+
+  if (*model) {
+    SceneNode* root = mem_get_node((*model)->root);
+    gfx_destroy_node(&root);
+    *model = 0;
+  }
+}
+
+Anima* gfx_get_model_anima(Model* model) {
+  assert(model);
+
+  SceneNode* root = mem_get_node(model->root);
+  if (gfx_get_node_type(root) == AnimaNode) {
+    return gfx_get_node_anima_mut(root);
+  } else {
+    return 0;
+  }
+}
+
+const SceneNode* gfx_get_model_root(const Model* model) {
+  assert(model);
+  return mem_get_node(model->root);
+}
+
+SceneNode* gfx_get_model_root_mut(Model* model) {
+  return (SceneNode*)gfx_get_model_root(model);
+}
diff --git a/src/scene/model_impl.h b/src/scene/model_impl.h
new file mode 100644
index 0000000..a99d32c
--- /dev/null
+++ b/src/scene/model_impl.h
@@ -0,0 +1,17 @@
+#pragma once
+
+#include <gfx/scene/model.h>
+
+#include "scene_memory.h"
+
+/// Model.
+typedef struct Model {
+  node_idx root;
+  node_idx parent; // Parent SceneNode.
+} Model;
+
+/// Create a new model.
+Model* gfx_make_model(const SceneNode* root);
+
+/// Destroy the model.
+void gfx_del_model(Model**);
diff --git a/src/scene/node.c b/src/scene/node.c
new file mode 100644
index 0000000..67ce93c
--- /dev/null
+++ b/src/scene/node.c
@@ -0,0 +1,409 @@
+#include "node_impl.h"
+
+#include "animation_impl.h"
+#include "camera_impl.h"
+#include "light_impl.h"
+#include "model_impl.h"
+#include "object_impl.h"
+#include "scene_graph.h"
+#include "scene_memory.h"
+
+#include "gfx_assert.h"
+
+#include <cstring.h>
+#include <log/log.h>
+
+static void scene_node_make(SceneNode* node) {
+  assert(node);
+  node->type      = LogicalNode;
+  node->transform = mat4_id();
+}
+
+SceneNode* gfx_make_node() {
+  SceneNode* node = mem_alloc_node();
+  scene_node_make(node);
+  return node;
+}
+
+SceneNode* gfx_make_anima_node(Anima* anima) {
+  assert(anima);
+  SceneNode* node = gfx_make_node();
+  node->type      = AnimaNode;
+  node->anima     = mem_get_anima_index(anima);
+  anima->parent   = mem_get_node_index(node);
+  return node;
+}
+
+SceneNode* gfx_make_camera_node(SceneCamera* camera) {
+  assert(camera);
+  SceneNode* node = gfx_make_node();
+  node->type      = CameraNode;
+  node->camera    = mem_get_camera_index(camera);
+  camera->parent  = mem_get_node_index(node);
+  return node;
+}
+
+SceneNode* gfx_make_light_node(Light* light) {
+  assert(light);
+  SceneNode* node = gfx_make_node();
+  node->type      = LightNode;
+  node->light     = mem_get_light_index(light);
+  light->parent   = mem_get_node_index(node);
+  return node;
+}
+
+SceneNode* gfx_make_model_node(Model* model) {
+  assert(model);
+  SceneNode* node = gfx_make_node();
+  node->type      = ModelNode;
+  node->model     = mem_get_model_index(model);
+  model->parent   = mem_get_node_index(node);
+  return node;
+}
+
+SceneNode* gfx_make_object_node(SceneObject* object) {
+  assert(object);
+  SceneNode* node = gfx_make_node();
+  node->type      = ObjectNode;
+  node->object    = mem_get_object_index(object);
+  object->parent  = mem_get_node_index(node);
+  return node;
+}
+
+/// Frees the node's resource.
+static void free_node_resource(SceneNode* node) {
+  assert(node);
+
+  // Set the resource's parent node back to 0 to avoid a recursive call into
+  // gfx_del_node().
+  switch (node->type) {
+  case AnimaNode: {
+    Anima* anima      = mem_get_anima(node->anima);
+    anima->parent.val = 0;
+    gfx_destroy_anima(&anima);
+    return;
+  }
+  case CameraNode: {
+    SceneCamera* camera = mem_get_camera(node->camera);
+    camera->parent.val  = 0;
+    gfx_destroy_camera(&camera);
+    return;
+  }
+  case LightNode: {
+    Light* light      = mem_get_light(node->light);
+    light->parent.val = 0;
+    gfx_destroy_light(&light);
+    return;
+  }
+  case ModelNode: {
+    return; // Model data is owned by the asset cache.
+  }
+  case ObjectNode: {
+    SceneObject* object = mem_get_object(node->object);
+    object->parent.val  = 0;
+    gfx_destroy_object(&object);
+    return;
+  }
+  case LogicalNode:
+    return; // Logical nodes have no resource.
+  }
+  FAIL("unhandled node type");
+}
+
+void gfx_construct_anima_node(SceneNode* node, Anima* anima) {
+  assert(node);
+  assert(anima);
+  free_node_resource(node);
+  node->type    = AnimaNode;
+  node->anima   = mem_get_anima_index(anima);
+  anima->parent = mem_get_node_index(node);
+}
+
+void gfx_construct_camera_node(SceneNode* node, SceneCamera* camera) {
+  assert(node);
+  assert(camera);
+  free_node_resource(node);
+  node->type     = CameraNode;
+  node->camera   = mem_get_camera_index(camera);
+  camera->parent = mem_get_node_index(node);
+}
+
+// TODO: Add a common helper function between each gfx_make_xyz_node() and
+//  gfx_construct_xyz_node() pair.
+void gfx_construct_light_node(SceneNode* node, Light* light) {
+  assert(node);
+  assert(light);
+  free_node_resource(node);
+  node->type    = LightNode;
+  node->light   = mem_get_light_index(light);
+  light->parent = mem_get_node_index(node);
+}
+
+void gfx_construct_model_node(SceneNode* node, Model* model) {
+  assert(node);
+  assert(model);
+  free_node_resource(node);
+  node->type    = ModelNode;
+  node->model   = mem_get_model_index(model);
+  model->parent = mem_get_node_index(node);
+}
+
+void gfx_construct_object_node(SceneNode* node, SceneObject* object) {
+  assert(node);
+  assert(object);
+  free_node_resource(node);
+  node->type     = ObjectNode;
+  node->object   = mem_get_object_index(object);
+  object->parent = mem_get_node_index(node);
+}
+
+static void destroy_node_rec(SceneNode* node) {
+  assert(node);
+
+  // First child.
+  if (node->child.val) {
+    destroy_node_rec(mem_get_node(node->child));
+  }
+
+  // Right sibling.
+  if (node->next.val) {
+    destroy_node_rec(mem_get_node(node->next));
+  }
+
+  free_node_resource(node);
+  mem_free_node(&node);
+}
+
+void gfx_destroy_node(SceneNode** node) {
+  assert(node);
+  if (*node) {
+    // Since the node and the whole hierarchy under it gets destroyed, there is
+    // no need to individually detach every node from its hierarchy. We can
+    // simply detach the given node and then destroy it and its sub-hierarchy.
+    TREE_REMOVE(*node);
+    destroy_node_rec(*node);
+    *node = 0;
+  }
+}
+
+// TODO: Think more about ownership of nodes and resources. Should this function
+//  even exist?
+void gfx_del_node(node_idx index) {
+  assert(index.val);
+  SceneNode* node = mem_get_node(index);
+  assert(node);
+  // TODO: Should destroy children recursively?
+  TREE_REMOVE(node);
+  mem_free_node(&node);
+}
+
+NodeType gfx_get_node_type(const SceneNode* node) {
+  assert(node);
+  return node->type;
+}
+
+#define NODE_GET(node, field, expected_type) \
+  {                                          \
+    assert(node);                            \
+    assert(node->type == expected_type);     \
+    return mem_get_##field(node->field);     \
+  }
+
+const Anima* gfx_get_node_anima(const SceneNode* node) {
+  NODE_GET(node, anima, AnimaNode);
+}
+
+Anima* gfx_get_node_anima_mut(SceneNode* node) {
+  NODE_GET(node, anima, AnimaNode);
+}
+
+const SceneCamera* gfx_get_node_camera(const SceneNode* node) {
+  NODE_GET(node, camera, CameraNode);
+}
+
+SceneCamera* gfx_get_node_camera_mut(SceneNode* node) {
+  NODE_GET(node, camera, CameraNode);
+}
+
+const Light* gfx_get_node_light(const SceneNode* node) {
+  NODE_GET(node, light, LightNode);
+}
+
+Light* gfx_get_node_light_mut(SceneNode* node) {
+  NODE_GET(node, light, LightNode);
+}
+
+const Model* gfx_get_node_model(const SceneNode* node) {
+  NODE_GET(node, model, ModelNode);
+}
+
+Model* gfx_get_node_model_mut(SceneNode* node) {
+  NODE_GET(node, model, ModelNode);
+}
+
+const SceneObject* gfx_get_node_object(const SceneNode* node) {
+  NODE_GET(node, object, ObjectNode);
+}
+
+SceneObject* gfx_get_node_object_mut(SceneNode* node) {
+  NODE_GET(node, object, ObjectNode);
+}
+
+const SceneNode* gfx_get_node_parent(const SceneNode* node) {
+  assert(node);
+  return mem_get_node(node->parent);
+}
+
+SceneNode* gfx_get_node_parent_mut(SceneNode* node) {
+  assert(node);
+  return mem_get_node(node->parent);
+}
+
+const SceneNode* gfx_get_node_child(const SceneNode* node) {
+  assert(node);
+  if (node->child.val) {
+    return mem_get_node(node->child);
+  } else {
+    return 0;
+  }
+}
+
+SceneNode* gfx_get_node_child_mut(SceneNode* node) {
+  return (SceneNode*)gfx_get_node_child(node);
+}
+
+const SceneNode* gfx_get_node_sibling(const SceneNode* node) {
+  assert(node);
+  if (node->next.val) {
+    return mem_get_node(node->next);
+  } else {
+    return 0;
+  }
+}
+
+SceneNode* gfx_get_node_sibling_mut(SceneNode* node) {
+  return (SceneNode*)gfx_get_node_sibling(node);
+}
+
+mat4 gfx_get_node_transform(const SceneNode* node) {
+  assert(node);
+  return node->transform;
+}
+
+mat4 gfx_get_node_global_transform(const SceneNode* node) {
+  assert(node);
+  mat4     transform    = node->transform;
+  node_idx parent_index = node->parent;
+  while (parent_index.val != 0) {
+    const SceneNode* parent = mem_get_node(parent_index);
+    transform               = mat4_mul(parent->transform, transform);
+    parent_index            = parent->parent;
+  }
+  return transform;
+}
+
+void gfx_set_node_parent(SceneNode* child, SceneNode* parent_node) {
+  assert(child);
+  // Parent can be null.
+  SET_PARENT(child, parent_node);
+}
+
+void gfx_set_node_transform(SceneNode* node, const mat4* transform) {
+  assert(node);
+  assert(transform);
+  node->transform = *transform;
+}
+
+void gfx_set_node_position(SceneNode* node, const vec3* position) {
+  assert(node);
+  assert(position);
+  mat4_set_v3(&node->transform, *position);
+}
+
+void gfx_set_node_rotation(SceneNode* node, const quat* rotation) {
+  assert(node);
+  assert(rotation);
+  mat4_set_3x3(&node->transform, mat4_from_quat(*rotation));
+}
+
+void gfx_set_node_rotation_mat(SceneNode* node, const mat4* rotation) {
+  assert(node);
+  assert(rotation);
+  mat4_set_3x3(&node->transform, *rotation);
+}
+
+static const char* get_node_type_str(NodeType type) {
+  switch (type) {
+  case LogicalNode:
+    return "LogicalNode";
+  case AnimaNode:
+    return "AnimaNode";
+  case CameraNode:
+    return "CameraNode";
+  case LightNode:
+    return "LightNode";
+  case ModelNode:
+    return "ModelNode";
+  case ObjectNode:
+    return "ObjectNode";
+  }
+  FAIL("Unhandled node type");
+  return "";
+}
+
+static void log_node_hierarchy_rec(const SceneNode* node, const sstring* pad) {
+  assert(node);
+  assert(pad);
+
+  LOGI(
+      "%s%s (%u)", sstring_cstr(pad), get_node_type_str(node->type),
+      mem_get_node_index(node).val);
+
+  // Log the children.
+  if (node->child.val) {
+    const sstring new_pad = sstring_concat_cstr(*pad, "  ");
+    log_node_hierarchy_rec(mem_get_node(node->child), &new_pad);
+  }
+
+  // Then log the siblings.
+  if (node->next.val) {
+    log_node_hierarchy_rec(mem_get_node(node->next), pad);
+  }
+}
+
+void gfx_log_node_hierarchy(const SceneNode* node) {
+  const sstring pad = sstring_make("");
+  log_node_hierarchy_rec(node, &pad);
+}
+
+static SceneNode* clone_scene_rec(const SceneNode* node) {
+  assert(node);
+
+  SceneNode* copy = mem_alloc_node();
+  *copy           = *node; // Shallow clone of the node's resource.
+
+  if (node->child.val) {
+    SceneNode* child      = mem_get_node(node->child);
+    SceneNode* child_copy = clone_scene_rec(child);
+    copy->child           = mem_get_node_index(child_copy);
+    child_copy->parent    = mem_get_node_index(copy);
+  }
+
+  if (node->next.val) {
+    SceneNode* next      = mem_get_node(node->next);
+    SceneNode* next_copy = clone_scene_rec(next);
+    copy->next           = mem_get_node_index(next_copy);
+    next_copy->prev      = mem_get_node_index(copy);
+  }
+
+  return copy;
+}
+
+SceneNode* gfx_clone_scene_shallow(const SceneNode* node) {
+  assert(node);
+  // Must be a root node; not allowed to have siblings.
+  assert(!node->prev.val);
+  assert(!node->next.val);
+
+  return clone_scene_rec(node);
+}
diff --git a/src/scene/node_impl.h b/src/scene/node_impl.h
new file mode 100644
index 0000000..c79f252
--- /dev/null
+++ b/src/scene/node_impl.h
@@ -0,0 +1,40 @@
+#pragma once
+
+#include <gfx/scene/node.h>
+
+#include "types.h"
+
+#include <cstring.h>
+#include <math/mat4.h>
+
+/// Scene node.
+///
+/// The SceneNode owns its cameras, objects, lights and child nodes. These
+/// together form a strict tree hierarchy and not a more general DAG.
+typedef struct SceneNode {
+  NodeType type;
+  union {
+    anima_idx  anima;
+    camera_idx camera;
+    light_idx  light;
+    model_idx  model;
+    object_idx object;
+  };
+  mat4     transform; // Transformation for this node and its children.
+  node_idx parent;    // Parent SceneNode.
+  node_idx child;     // First child SceneNode.
+  node_idx next;      // Next sibling SceneNode.
+  node_idx prev;      // Previous sibling SceneNode.
+} SceneNode;
+
+/// Recursively destroy a node given its index but without destroying the node
+/// resources.
+///
+/// The node and its children are removed from the scene graph.
+///
+/// This function is for the library's internal use only.
+void gfx_del_node(node_idx);
+
+/// Return a shallow clone of the scene rooted at the given node.
+/// The given node must have no siblings (must be a root node).
+SceneNode* gfx_clone_scene_shallow(const SceneNode*);
diff --git a/src/scene/object.c b/src/scene/object.c
new file mode 100644
index 0000000..e8e3ee6
--- /dev/null
+++ b/src/scene/object.c
@@ -0,0 +1,83 @@
+#include "object_impl.h"
+
+#include <gfx/core.h>
+
+#include "mesh_impl.h"
+#include "node_impl.h"
+#include "scene_memory.h"
+
+#include <assert.h>
+
+static aabb3 calc_object_aabb(const SceneObject* object) {
+  assert(object);
+
+  bool  first = true;
+  aabb3 box;
+
+  mesh_link_idx ml = object->mesh_link;
+  while (ml.val) {
+    const MeshLink* mesh_link = mem_get_mesh_link(ml);
+    const mesh_idx  mi        = mesh_link->mesh;
+    if (mi.val) {
+      const Mesh* mesh     = mem_get_mesh(mi);
+      const aabb3 mesh_box = gfx_get_geometry_aabb(mesh->geometry);
+      if (first) {
+        box   = mesh_box;
+        first = false;
+      } else {
+        box = aabb3_sum(box, mesh_box);
+      }
+    }
+    ml = mesh_link->next;
+  }
+
+  return box;
+}
+
+static void add_object_mesh(SceneObject* object, Mesh* mesh) {
+  assert(object);
+  assert(mesh);
+
+  MeshLink* link    = mem_alloc_mesh_link();
+  link->mesh        = mem_get_mesh_index(mesh);
+  link->next        = object->mesh_link;
+  object->mesh_link = mem_get_mesh_link_index(link);
+}
+
+SceneObject* gfx_make_object(const ObjectDesc* desc) {
+  assert(desc);
+
+  SceneObject* object = mem_alloc_object();
+  for (size_t i = 0; i < desc->num_meshes; ++i) {
+    add_object_mesh(object, desc->meshes[i]);
+  }
+  object->box = calc_object_aabb(object);
+  return object;
+}
+
+void gfx_destroy_object(SceneObject** object) {
+  assert(object);
+
+  if (*object) {
+    if ((*object)->parent.val) {
+      gfx_del_node((*object)->parent);
+    }
+    mem_free_object(object);
+  }
+}
+
+void gfx_set_object_skeleton(SceneObject* object, const Skeleton* skeleton) {
+  assert(object);
+  assert(skeleton);
+  object->skeleton = mem_get_skeleton_index(skeleton);
+}
+
+const Skeleton* gfx_get_object_skeleton(const SceneObject* object) {
+  assert(object);
+  return (object->skeleton.val == 0) ? 0 : mem_get_skeleton(object->skeleton);
+}
+
+aabb3 gfx_get_object_aabb(const SceneObject* object) {
+  assert(object);
+  return object->box;
+}
diff --git a/src/scene/object_impl.h b/src/scene/object_impl.h
new file mode 100644
index 0000000..88f8e31
--- /dev/null
+++ b/src/scene/object_impl.h
@@ -0,0 +1,26 @@
+#pragma once
+
+#include <gfx/scene/object.h>
+
+#include "types.h"
+
+#include <math/mat4.h>
+
+typedef struct MeshLink {
+  mesh_idx      mesh;
+  mesh_link_idx next; // Next MeshLink in the list.
+} MeshLink;
+
+/// Scene object.
+///
+/// A SceneObject does not own its Meshes, and they are instead shared for
+/// re-use. The SceneObject consequently embeds a list of MeshLinks as opposed
+/// to a list of Meshes. The MeshLinks define a list of Meshes, which can be
+/// different for each SceneObject. Each SceneObject may then have a unique list
+/// of Meshes, and the Meshes are re-used.
+typedef struct SceneObject {
+  mesh_link_idx mesh_link; /// First MeshLink in the list.
+  skeleton_idx  skeleton;  /// 0 for static objects.
+  node_idx      parent;    /// Parent SceneNode.
+  aabb3         box;
+} SceneObject;
diff --git a/src/scene/scene.c b/src/scene/scene.c
new file mode 100644
index 0000000..54452dd
--- /dev/null
+++ b/src/scene/scene.c
@@ -0,0 +1,25 @@
+#include "scene_impl.h"
+
+#include "node_impl.h"
+#include "scene_memory.h"
+
+#include <assert.h>
+
+Scene* gfx_make_scene(void) {
+  Scene* scene = mem_alloc_scene();
+  scene->root  = gfx_make_node();
+  return scene;
+}
+
+void gfx_destroy_scene(Scene** scene) {
+  assert(scene);
+  if (*scene) {
+    gfx_destroy_node(&(*scene)->root);
+    mem_free_scene(scene);
+  }
+}
+
+SceneNode* gfx_get_scene_root(Scene* scene) {
+  assert(scene);
+  return scene->root;
+}
diff --git a/src/scene/scene_graph.h b/src/scene/scene_graph.h
new file mode 100644
index 0000000..a26f828
--- /dev/null
+++ b/src/scene/scene_graph.h
@@ -0,0 +1,138 @@
+/// Functions for list manipulation.
+#pragma once
+
+#include "scene_memory.h"
+
+// NOTE: SceneMemory guarantees that index 0 can be regarded as an invalid
+// index.
+
+#define MEM_GET(INDEX)                    \
+  _Generic((INDEX), camera_idx            \
+           : mem_get_camera, material_idx \
+           : mem_get_material, mesh_idx   \
+           : mem_get_mesh, mesh_link_idx  \
+           : mem_get_mesh_link, node_idx  \
+           : mem_get_node, object_idx     \
+           : mem_get_object, scene_idx    \
+           : mem_get_scene)(INDEX)
+
+#define MEM_GET_INDEX(ITEM)                       \
+  _Generic((ITEM), SceneCamera *                  \
+           : mem_get_camera_index, Material *     \
+           : mem_get_material_index, Mesh *       \
+           : mem_get_mesh_index, MeshLink *       \
+           : mem_get_mesh_link_index, SceneNode * \
+           : mem_get_node_index, SceneObject *    \
+           : mem_get_object_index, Scene *        \
+           : mem_get_scene_index)(ITEM)
+
+/// Assert the list node invariant.
+///
+/// - A node does not point to itself.
+#define ASSERT_LIST_NODE_INVARIANT(ITEM)              \
+  {                                                   \
+    const gfx_idx item_idx = MEM_GET_INDEX(ITEM).val; \
+    assert((ITEM)->prev.val != item_idx);             \
+    assert((ITEM)->next.val != item_idx);             \
+  }
+
+/// Assert the tree node invariant.
+///
+/// - A node does not point to itself.
+/// - The node's left and right siblings cannot be equal, unless both are 0.
+/// - The node's left/right sibling cannot be its child, unless both are 0.
+/// - The node's parent cannot be the node's child or sibling, unless it's 0.
+/// - If the node has a parent and the node is the leftmost sibling, then the
+///   parent's child is the node.
+#define ASSERT_TREE_NODE_INVARIANT(ITEM)                            \
+  {                                                                 \
+    const gfx_idx item_idx = MEM_GET_INDEX(ITEM).val;               \
+    assert((ITEM)->prev.val != item_idx);                           \
+    assert((ITEM)->next.val != item_idx);                           \
+    if ((ITEM)->prev.val) {                                         \
+      assert((ITEM)->prev.val != (ITEM)->next.val);                 \
+    }                                                               \
+    if ((ITEM)->child.val) {                                        \
+      assert((ITEM)->child.val != (ITEM)->prev.val);                \
+      assert((ITEM)->child.val != (ITEM)->next.val);                \
+    }                                                               \
+    assert((ITEM)->parent.val != item_idx);                         \
+    if ((ITEM)->parent.val && !(ITEM)->prev.val) {                  \
+      assert((ITEM)->parent.val != (ITEM)->prev.val);               \
+      assert((ITEM)->parent.val != (ITEM)->next.val);               \
+      const __typeof__(ITEM) item_parent = MEM_GET((ITEM)->parent); \
+      assert(item_parent->child.val == item_idx);                   \
+    }                                                               \
+  }
+
+/// Prepend an item to a list.
+/// Modify HEAD_INDEX to equal the index of the new head.
+#define LIST_PREPEND(HEAD_INDEX, ITEM)               \
+  (ITEM)->next = HEAD_INDEX;                         \
+  if (HEAD_INDEX.val) {                              \
+    __typeof__(ITEM) old_head = MEM_GET(HEAD_INDEX); \
+    old_head->prev            = MEM_GET_INDEX(ITEM); \
+  }                                                  \
+  HEAD_INDEX = MEM_GET_INDEX(ITEM);                  \
+  ASSERT_LIST_NODE_INVARIANT(ITEM);
+
+/// Disconnect an item from its siblings.
+#define LIST_REMOVE(ITEM)                                  \
+  if ((ITEM)->prev.val) {                                  \
+    __typeof__(ITEM) prev_sibling = MEM_GET((ITEM)->prev); \
+    prev_sibling->next            = (ITEM)->next;          \
+  }                                                        \
+  if ((ITEM)->next.val) {                                  \
+    __typeof__(ITEM) next_sibling = MEM_GET((ITEM)->next); \
+    next_sibling->prev            = (ITEM)->prev;          \
+  }                                                        \
+  (ITEM)->prev.val = 0;                                    \
+  (ITEM)->next.val = 0;                                    \
+  ASSERT_LIST_NODE_INVARIANT(ITEM);
+
+/// Set the child's parent.
+///
+/// The hierarchy is a strict tree hierarchy and a parent node points to its
+/// first/leftmost child only. To add a new child, the new child becomes the
+/// leftmost node in the list of siblings, the one that the parent then points
+/// to.
+///
+/// The child is also completely disconnected from its previous hierarchy. This
+/// is because siblings in a hierarchy must all point to the same parent.
+#define SET_PARENT(CHILD, PARENT)                                         \
+  assert(CHILD);                                                          \
+  assert(CHILD != PARENT);                                                \
+  ASSERT_TREE_NODE_INVARIANT(CHILD);                                      \
+  ASSERT_TREE_NODE_INVARIANT(PARENT);                                     \
+  TREE_REMOVE(CHILD); /* Disconnect CHILD from its previous hierarchy. */ \
+  if (PARENT) {                                                           \
+    LIST_PREPEND((PARENT)->child, CHILD);                                 \
+    (CHILD)->parent = MEM_GET_INDEX(PARENT);                              \
+  } else {                                                                \
+    (CHILD)->parent.val = 0;                                              \
+  }                                                                       \
+  ASSERT_TREE_NODE_INVARIANT(CHILD);                                      \
+  if (PARENT) {                                                           \
+    ASSERT_TREE_NODE_INVARIANT(PARENT);                                   \
+  }
+
+/// Remove an item from its hierarchy.
+///
+/// The item is disconnected from its parents and siblings. The hierarchy rooted
+/// under the item remains intact.
+#define TREE_REMOVE(ITEM)                                                     \
+  assert(ITEM);                                                               \
+  if ((ITEM)->parent.val) {                                                   \
+    /* The parent points only to its first/leftmost child. If this item is */ \
+    /* the leftmost sibling, then we need to rewire the parent to point to */ \
+    /* the next sibling to keep the parent connected to its children. */      \
+    __typeof__(ITEM)       parent       = MEM_GET((ITEM)->parent);            \
+    const __typeof__(ITEM) parent_child = MEM_GET(parent->child);             \
+    if (parent_child == ITEM) {                                               \
+      assert((ITEM)->prev.val == 0);                                          \
+      parent->child = (ITEM)->next;                                           \
+    }                                                                         \
+  }                                                                           \
+  (ITEM)->parent.val = 0;                                                     \
+  LIST_REMOVE(ITEM); /* Disconnect ITEM from its siblings. */                 \
+  ASSERT_TREE_NODE_INVARIANT(ITEM);
diff --git a/src/scene/scene_impl.h b/src/scene/scene_impl.h
new file mode 100644
index 0000000..992f620
--- /dev/null
+++ b/src/scene/scene_impl.h
@@ -0,0 +1,13 @@
+#pragma once
+
+#include <gfx/scene/scene.h>
+
+#include "types.h"
+
+typedef struct SceneNode SceneNode;
+
+typedef struct Scene {
+  SceneNode* root;
+  scene_idx  next;
+  scene_idx  prev;
+} Scene;
diff --git a/src/scene/scene_memory.c b/src/scene/scene_memory.c
new file mode 100644
index 0000000..85c27e7
--- /dev/null
+++ b/src/scene/scene_memory.c
@@ -0,0 +1,149 @@
+#include "scene_memory.h"
+
+#include <gfx/sizes.h>
+
+#include "animation_impl.h"
+#include "camera_impl.h"
+#include "light_impl.h"
+#include "material_impl.h"
+#include "mesh_impl.h"
+#include "model_impl.h"
+#include "node_impl.h"
+#include "object_impl.h"
+#include "scene_impl.h"
+
+#include <mempool.h>
+
+DEF_MEMPOOL(anima_pool, Anima, GFX_MAX_NUM_ANIMAS)
+DEF_MEMPOOL(animation_pool, Animation, GFX_MAX_NUM_ANIMATIONS)
+DEF_MEMPOOL(camera_pool, SceneCamera, GFX_MAX_NUM_CAMERAS)
+DEF_MEMPOOL(light_pool, Light, GFX_MAX_NUM_LIGHTS)
+DEF_MEMPOOL(material_pool, Material, GFX_MAX_NUM_MATERIALS)
+DEF_MEMPOOL(mesh_pool, Mesh, GFX_MAX_NUM_MESHES)
+DEF_MEMPOOL(mesh_link_pool, MeshLink, GFX_MAX_NUM_MESH_LINKS)
+DEF_MEMPOOL(model_pool, Model, GFX_MAX_NUM_MODELS)
+DEF_MEMPOOL(node_pool, SceneNode, GFX_MAX_NUM_NODES)
+DEF_MEMPOOL(object_pool, SceneObject, GFX_MAX_NUM_OBJECTS)
+DEF_MEMPOOL(scene_pool, Scene, GFX_MAX_NUM_SCENES)
+DEF_MEMPOOL(skeleton_pool, Skeleton, GFX_MAX_NUM_SKELETONS)
+
+/// Scene memory.
+///
+/// Holds memory pools for every type of scene object.
+typedef struct SceneMemory {
+  anima_pool     animas;
+  animation_pool animations;
+  camera_pool    cameras;
+  light_pool     lights;
+  material_pool  materials;
+  mesh_pool      meshs; // Purposeful typo to make the PLURAL() macro work.
+  mesh_link_pool mesh_links;
+  model_pool     models;
+  node_pool      nodes;
+  object_pool    objects;
+  scene_pool     scenes;
+  skeleton_pool  skeletons;
+} SceneMemory;
+
+static SceneMemory mem;
+
+#define ALLOC_DUMMY(POOL)                               \
+  {                                                     \
+    const void* object = mempool_alloc(POOL);           \
+    assert(mempool_get_block_index(POOL, object) == 0); \
+  }
+
+#define PLURAL(name)    name##s
+#define MEM_FIELD(name) mem.PLURAL(name)
+
+void scene_mem_init() {
+  mempool_make(&mem.animas);
+  mempool_make(&mem.animations);
+  mempool_make(&mem.cameras);
+  mempool_make(&mem.lights);
+  mempool_make(&mem.materials);
+  mempool_make(&mem.meshs);
+  mempool_make(&mem.mesh_links);
+  mempool_make(&mem.models);
+  mempool_make(&mem.nodes);
+  mempool_make(&mem.objects);
+  mempool_make(&mem.scenes);
+  mempool_make(&mem.skeletons);
+
+  // Allocate dummy objects at index 0 to guarantee that no objects allocated by
+  // the caller map to index 0.
+  ALLOC_DUMMY(&mem.animas);
+  ALLOC_DUMMY(&mem.animations);
+  ALLOC_DUMMY(&mem.cameras);
+  ALLOC_DUMMY(&mem.lights);
+  ALLOC_DUMMY(&mem.materials);
+  ALLOC_DUMMY(&mem.meshs);
+  ALLOC_DUMMY(&mem.mesh_links);
+  ALLOC_DUMMY(&mem.models);
+  ALLOC_DUMMY(&mem.nodes);
+  ALLOC_DUMMY(&mem.objects);
+  ALLOC_DUMMY(&mem.scenes);
+  ALLOC_DUMMY(&mem.skeletons);
+}
+
+void scene_mem_destroy() {
+  // NOTE: the dummy objects are not constructed, so the destruction code below
+  // always skips index 0. (I don't really like the conditional inside the loop,
+  // but this gets the job done without having to specialize the loop macro.)
+#define DESTROY(name)                      \
+  mempool_foreach(&MEM_FIELD(name), obj, { \
+    if (i > 0) {                           \
+      gfx_destroy_##name(&obj);            \
+    }                                      \
+  })
+
+  // Models contain scene elements. Destruction is handled by the remainder of
+  // scene destructionb elow.
+  //
+  // First destroy the scenes. This will recursively destroy the scene's nodes
+  // and their objects and avoid a double-free when we then destroy any stray
+  // scene elements.
+  DESTROY(scene);
+  // Then delete stray nodes. This will delete their children nodes and
+  // resource.
+  DESTROY(node);
+  // Destroy remaining scene elements.
+  DESTROY(anima);
+  // Animations are owned by animas and do not have a destructor.
+  DESTROY(camera);
+  DESTROY(light);
+  DESTROY(material);
+  DESTROY(mesh);
+  // Mesh links don't have a destructor.
+  DESTROY(object);
+  // Skeletons are owned by animas and do not have a destructor.
+}
+
+#define DEF_MEMORY(name, type)                                              \
+  /* xyz* mem_alloc_xyz(); */                                               \
+  type* mem_alloc_##name() { return mempool_alloc(&MEM_FIELD(name)); }      \
+  /* void mem_free_xyz(xyz**); */                                           \
+  void mem_free_##name(type** obj) { mempool_free(&MEM_FIELD(name), obj); } \
+  /* xyz* mem_get_xyz(xyz_idx); */                                          \
+  type* mem_get_##name(NAMED_INDEX(name) index) {                           \
+    assert(index.val != 0); /* 0 is the dummy allocation. */                \
+    return mempool_get_block(&MEM_FIELD(name), index.val);                  \
+  }                                                                         \
+  /* xyz_idx mem_get_xyz_index(const xyz*); */                              \
+  NAMED_INDEX(name) mem_get_##name##_index(const type* obj) {               \
+    return (NAMED_INDEX(name)){                                             \
+        .val = mempool_get_block_index(&MEM_FIELD(name), obj)};             \
+  }
+
+DEF_MEMORY(anima, Anima)
+DEF_MEMORY(animation, Animation)
+DEF_MEMORY(camera, SceneCamera)
+DEF_MEMORY(light, Light)
+DEF_MEMORY(material, Material)
+DEF_MEMORY(mesh, Mesh)
+DEF_MEMORY(mesh_link, MeshLink)
+DEF_MEMORY(model, Model)
+DEF_MEMORY(node, SceneNode)
+DEF_MEMORY(object, SceneObject)
+DEF_MEMORY(scene, Scene)
+DEF_MEMORY(skeleton, Skeleton)
diff --git a/src/scene/scene_memory.h b/src/scene/scene_memory.h
new file mode 100644
index 0000000..d175cba
--- /dev/null
+++ b/src/scene/scene_memory.h
@@ -0,0 +1,39 @@
+/// Memory management of scene objects.
+#pragma once
+
+#include "types.h"
+
+/// Initialize scene memory.
+///
+/// The scene memory guarantees that every object maps to an index different
+/// than 0. This way, 0 can be used as a special index to denote "no value".
+void scene_mem_init();
+
+/// Destroy the scene memory and all allocated objects.
+void scene_mem_destroy();
+
+#define NAMED_INDEX(name) name##_idx
+
+#define DECL_MEMORY(name, type)                \
+  typedef struct type type;                    \
+  /* xyz* mem_alloc_xyz() */                   \
+  type* mem_alloc_##name();                    \
+  /* mem_free_xyz(xyz**) */                    \
+  void mem_free_##name(type**);                \
+  /* xyz* mem_get_xyz(xyz_idx); */             \
+  type* mem_get_##name(NAMED_INDEX(name));     \
+  /* xyz_idx mem_get_xyz_index(const xyz*); */ \
+  NAMED_INDEX(name) mem_get_##name##_index(const type*);
+
+DECL_MEMORY(anima, Anima)
+DECL_MEMORY(animation, Animation)
+DECL_MEMORY(camera, SceneCamera)
+DECL_MEMORY(light, Light)
+DECL_MEMORY(material, Material)
+DECL_MEMORY(mesh, Mesh)
+DECL_MEMORY(mesh_link, MeshLink)
+DECL_MEMORY(model, Model)
+DECL_MEMORY(node, SceneNode)
+DECL_MEMORY(object, SceneObject)
+DECL_MEMORY(scene, Scene)
+DECL_MEMORY(skeleton, Skeleton)
diff --git a/src/scene/types.h b/src/scene/types.h
new file mode 100644
index 0000000..d0ffc41
--- /dev/null
+++ b/src/scene/types.h
@@ -0,0 +1,24 @@
+/// Strongly-typed indices for every kind of scene node resource.
+#pragma once
+
+#include <stdint.h>
+
+typedef uint16_t gfx_idx;
+
+#define DEF_STRONG_INDEX(TYPE_NAME, IDX_TYPE) \
+  typedef struct TYPE_NAME##_idx {            \
+    IDX_TYPE val;                             \
+  } TYPE_NAME##_idx;
+
+DEF_STRONG_INDEX(anima, gfx_idx)
+DEF_STRONG_INDEX(animation, gfx_idx)
+DEF_STRONG_INDEX(camera, gfx_idx)
+DEF_STRONG_INDEX(light, gfx_idx)
+DEF_STRONG_INDEX(material, gfx_idx)
+DEF_STRONG_INDEX(mesh, gfx_idx)
+DEF_STRONG_INDEX(mesh_link, gfx_idx)
+DEF_STRONG_INDEX(model, gfx_idx)
+DEF_STRONG_INDEX(node, gfx_idx)
+DEF_STRONG_INDEX(object, gfx_idx)
+DEF_STRONG_INDEX(scene, gfx_idx)
+DEF_STRONG_INDEX(skeleton, gfx_idx)