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diff --git a/src/render/llr_impl.h b/src/render/llr_impl.h
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+++ b/src/render/llr_impl.h
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+#pragma once
+
+#include <gfx/render/llr.h>
+#include <gfx/sizes.h>
+
+#include <math/mat4.h>
+#include <math/vec3.h>
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+
+typedef struct GfxCore       GfxCore;
+typedef struct IBL           IBL;
+typedef struct Material      Material;
+typedef struct ShaderProgram ShaderProgram;
+typedef struct Texture       Texture;
+
+/// Immediate mode renderer.
+///
+/// The renderer caches state changes in memory and only programs the underlying
+/// shader program when a draw call is issued and if anything has changed. This
+/// keeps the number of graphics API calls to a minimum, but requires tracking
+/// state changes. The 'changed' booleans below fulfill this purpose, and
+/// indicate whether a given state has changed since the last draw call.
+///
+/// The renderer must combine state changes accordingly. For example, if only
+/// the lights have changed, then it is sufficient to update light uniforms in
+/// the current shader program. On the other hand, if the shader program has
+/// changed, then the renderer must reconfigure it from scratch and set light
+/// uniforms, camera uniforms, etc.
+///
+/// Note that the shader program API has its own level of caching as well, so
+/// reconfiguration at the level of the renderer does not result in the
+/// worst-case set of graphics API calls.
+typedef struct LLR {
+  GfxCore* gfxcore;
+
+  union {
+    struct {
+      bool shader_changed   : 1; // Whether the shader has changed.
+      bool camera_changed   : 1; // Whether the camera parameters have changed.
+      bool lights_changed   : 1; // Whether the lights have changed.
+      bool skeleton_changed : 1; // Whether the skeleton has changed.
+      bool material_changed : 1; // Whether the material has changed.
+      bool matrix_changed   : 1; // Whether the matrix stack has changed.
+    };
+    uint8_t changed_flags;
+  };
+
+  IBL*     ibl;
+  Texture* brdf_integration_map;
+
+  ShaderProgram* shader; // Active shader. Not owned.
+
+  const Material* material; // Active material. Not owned.
+
+  vec3 camera_position;
+  mat4 camera_rotation;
+  mat4 view;       // Camera view matrix.
+  mat4 projection; // Camera projection matrix.
+  R    fovy;       // Camera vertical field of view.
+  R    aspect;     // Aspect ratio.
+
+  // Lights are not const because environment lights store lazily-computed
+  // irradiance maps.
+  Light* lights[GFX_LLR_MAX_NUM_LIGHTS]; // Lights stack.
+  int    num_lights; // Number of lights enabled at a given point in time. It
+                     // points to one past the top of the stack.
+
+  size_t num_joints;
+  mat4   joint_matrices[GFX_MAX_NUM_JOINTS];
+
+  // The matrix stack contains pre-multiplied matrices.
+  // It is also never empty. The top of the stack is an identity matrix when the
+  // stack is "empty" from the user's perspective.
+  mat4 matrix_stack[GFX_LLR_MAX_NUM_MATRICES];
+  int  stack_pointer; // Points to the top of the stack.
+} LLR;
+
+/// Create a new immediate mode renderer.
+bool gfx_llr_make(LLR*, GfxCore*);
+
+/// Destroy the immediate mode renderer.
+void gfx_llr_destroy(LLR*);