21 files changed, 846 insertions, 0 deletions

diff --git a/shaders/brdf_integration_map.frag b/shaders/brdf_integration_map.frag
new file mode 100644
index 0000000..bb2cebd
--- /dev/null
+++ b/shaders/brdf_integration_map.frag
@@ -0,0 +1,93 @@
+precision highp float;
+
+#define PI 3.1415926535897932384626433832795
+#define NUM_SAMPLES 1024
+
+in vec2 Texcoord;
+
+layout (location = 0) out vec2 Color;
+
+float radical_inverse_VdC(uint bits) {
+    bits = (bits << 16u) | (bits >> 16u);
+    bits = ((bits & 0x55555555u) << 1u) | ((bits & 0xAAAAAAAAu) >> 1u);
+    bits = ((bits & 0x33333333u) << 2u) | ((bits & 0xCCCCCCCCu) >> 2u);
+    bits = ((bits & 0x0F0F0F0Fu) << 4u) | ((bits & 0xF0F0F0F0u) >> 4u);
+    bits = ((bits & 0x00FF00FFu) << 8u) | ((bits & 0xFF00FF00u) >> 8u);
+    return float(bits) * 2.3283064365386963e-10; // / 0x100000000
+}
+
+vec2 hammersley(uint i, uint N) {
+    return vec2(float(i)/float(N), radical_inverse_VdC(i));
+}
+
+vec3 importance_sample_GGX(vec2 sample_box, vec3 N, float roughness) {
+  float r2 = roughness * roughness;
+
+  // Spherical coordinates.
+  float phi = 2.0 * PI * sample_box.x;
+  float cos_theta = sqrt((1.0 - sample_box.y) / (1.0 + (r2*r2 - 1.0) * sample_box.y));
+  float sin_theta = sqrt(1.0 - cos_theta * cos_theta);
+
+  // Map spherical coordinates to Cartesian coordinates in tangent space.
+  vec3 H = vec3(cos(phi) * sin_theta, sin(phi) * sin_theta, cos_theta);
+
+  // Map from tangent space to world space.
+  //
+  // Tangent space:
+  //
+  //        N
+  //        |
+  //        |
+  //        |
+  //        |_ _ _ _ _ B
+  //       /
+  //      /
+  //     T
+  vec3 up = abs(N.z) < 0.999 ? vec3(0.0, 0.0, 1.0) : vec3(1.0, 0.0, 0.0);
+  vec3 T = normalize(cross(up,N));
+  vec3 B = cross(N,T);
+  vec3 H_ws = H.x*T + H.y*B + H.z*N;
+  return H_ws;
+}
+
+float geometry_schlick_GGX(float k, float NdotV) {
+  return NdotV / (NdotV * (1.0 - k) + k);
+}
+
+float geometry_smith(float roughness, float NdotL, float NdotV) {
+  float k = roughness * roughness / 2.0; // IBL
+  return geometry_schlick_GGX(k, NdotV) * geometry_schlick_GGX(k, NdotL);
+}
+
+vec2 integrate_brdf(float NdotV, float roughness)
+{
+  vec3 V = vec3(sqrt(1.0 - NdotV * NdotV), 0.0, NdotV);
+  vec3 N = vec3(0.0, 0.0, 1.0);
+
+  float scale = 0.0;
+  float bias = 0.0;
+  for (int i = 0; i < NUM_SAMPLES; ++i) {
+    vec2 sample_box = hammersley(i, NUM_SAMPLES);
+    vec3 H = importance_sample_GGX(sample_box, N, roughness);
+    vec3 L = reflect(-V,H);
+    float NdotL = max(0.0, L.z);
+
+    if (NdotL > 0.0) {
+      float NdotH = max(0.0, H.z);
+      float VdotH = max(0.0, dot(V,H));
+      float G = geometry_smith(roughness, NdotL, NdotV);
+      float G_vis = (G * VdotH) / (NdotH * NdotV);
+      float Fc = pow(1.0 - VdotH, 5.0);
+      scale += (1.0 - Fc) * G_vis;
+      bias  += Fc * G_vis;
+    }
+  }
+  scale /= float(NUM_SAMPLES);
+  bias  /= float(NUM_SAMPLES);
+  return vec2(scale, bias);
+}
+
+void main()
+{
+  Color = integrate_brdf(Texcoord.x, Texcoord.y);
+}
diff --git a/shaders/cook_torrance.frag b/shaders/cook_torrance.frag
new file mode 100644
index 0000000..1975491
--- /dev/null
+++ b/shaders/cook_torrance.frag
@@ -0,0 +1,255 @@
+precision highp float;
+
+uniform vec4  BaseColorFactor;
+uniform float MetallicFactor;
+uniform float RoughnessFactor;
+uniform vec3  EmissiveFactor;
+
+#ifdef HAS_ALBEDO_MAP
+uniform sampler2D BaseColorTexture;
+#endif
+#ifdef HAS_METALLIC_ROUGHNESS_MAP
+uniform sampler2D MetallicRoughnessTexture;
+#endif
+#ifdef HAS_EMISSIVE_MAP
+uniform sampler2D EmissiveTexture;
+#endif
+#ifdef HAS_OCCLUSION_MAP
+uniform sampler2D AmbientOcclusionTexture;
+#endif
+#ifdef HAS_NORMAL_MAP
+uniform sampler2D NormalMap;
+#endif
+
+// TODO: Handle case in which there is no sky. Pass a boolean.
+uniform samplerCube Sky;
+uniform samplerCube IrradianceMap;
+uniform samplerCube PrefilteredEnvironmentMap;
+uniform sampler2D   BRDFIntegrationMap;
+uniform float       MaxReflectionLOD;
+
+uniform vec3 CameraPosition; // World space.
+
+// World-space position, normal and tangent.
+in vec3 Position;
+#ifdef HAS_NORMALS
+in vec3 Normal;
+#endif
+#ifdef HAS_TANGENTS
+in vec4 Tangent;
+#endif
+#ifdef HAS_TEXCOORDS
+in vec2 Texcoord;
+#endif
+
+layout (location = 0) out vec4 Colour;
+
+#define PI 3.1415926535897932384626433832795
+#define INV_PI 0.3183098861837907
+
+/// Transform a normal map sample into world space.
+///
+/// |normalWs| is the surface normal in world space.
+/// |normalMapSample| is the normal map sample, not necessarily normalized.
+///
+/// TODO: Move to "normal.h"
+#if defined(HAS_NORMAL_MAP) && (defined(HAS_TANGENTS) || defined(HAS_TEXCOORDS))
+vec3 get_ws_normal(vec3 normalWs, vec3 normalMapSample) {
+  vec3 N = normalize(Normal);
+#ifdef HAS_TANGENTS
+  //vec3 T = normalize(tangent.xyz - dot(tangent.xyz, N) * N);
+  vec3 T = Tangent.xyz;
+  vec3 B = Tangent.w * cross(N, T);
+#elif HAS_TEXCOORDS // No tangents, but must have texcoords.
+  vec3 pos_dx = dFdx(Position);
+  vec3 pos_dy = dFdy(Position);
+  // vec3 uv_dx = vec3(dFdx(Texcoord), 0.0);
+  // vec3 uv_dy = vec3(dFdy(Texcoord), 0.0);
+  vec3 uv_dx = dFdx(vec3(Texcoord, 0.0));
+  vec3 uv_dy = dFdy(vec3(Texcoord, 0.0));
+  vec3 T = (uv_dy.t * pos_dx - uv_dx.t * pos_dy) /
+           (uv_dx.s * uv_dy.t - uv_dy.s * uv_dx.t);
+  // vec3 T = pos_dx * uv_dy.t - pos_dy * uv_dx.t;
+  T = normalize(T - dot(T, N) * N);
+  vec3 B = normalize(cross(N, T));
+#endif
+
+  if (gl_FrontFacing == false) {
+    T = -T;
+    B = -B;
+    N = -N;
+  }
+
+  vec3 s = normalMapSample;
+  //return normalize(s.x * T + s.y * B + s.z * N);
+  return normalize(mat3(T,B,N) * s);
+}
+#endif // HAS_TANGENTS || HAS_TEXCOORDS
+
+float trowbridge_reitz_GGX(float roughness, float NdotH) {
+  float a = roughness * roughness;
+  float a2 = a * a;
+  float d = NdotH * NdotH * (a2 - 1.0) + 1.0;
+  return a2 / (PI * d * d);
+}
+
+float geometry_schlick_GGX(float k, float NdotV) {
+  return NdotV / (NdotV * (1.0 - k) + k);
+}
+
+float geometry_smith(float roughness, float NdotL, float NdotV) {
+  float k = roughness * roughness / 2.0; // IBL
+  return geometry_schlick_GGX(k, NdotV) * geometry_schlick_GGX(k, NdotL);
+}
+
+vec3 fresnel_schlick(vec3 F0, float HdotV) {
+  return F0 + (1.0 - F0) * pow(clamp(1.0 - HdotV, 0.0, 1.0), 5.0);
+}
+
+vec3 fresnel_schlick_roughness(vec3 F0, float NdotV, float roughness) {
+  return F0
+    + (max(vec3(1.0 - roughness), F0) - F0)
+    * pow(clamp(1.0 - NdotV, 0.0, 1.0), 5.0);
+}
+
+// Cook-Torrance BRDF for a single light direction.
+vec3 cook_torrance(
+    vec3 albedo, float metallic, float roughness,
+    float NdotL, float NdotV, float NdotH, float HdotV) {
+  vec3 F0 = mix(vec3(0.04), albedo, metallic);
+  float D = trowbridge_reitz_GGX(roughness, NdotH);
+  vec3  F = fresnel_schlick(F0, HdotV);
+  float G = geometry_smith(roughness, NdotL, NdotV);
+  vec3 Kd = mix(vec3(1.0) - F, vec3(0.0), metallic);
+  vec3 diffuse = Kd*albedo*INV_PI;
+  // Take a max to prevent division by 0 when either dot product is 0.
+  vec3 specular = (D*F*G) / max(4.0 * NdotV * NdotL, 0.0001);
+  return diffuse + specular;
+}
+
+// Cook-Torrance BRDF for IBL.
+vec3 cook_torrance_IBL(
+    vec3 albedo, float metallic, float roughness, float occlusion,
+    float NdotV,
+    vec3 irradiance, vec3 prefiltered_env, vec2 BRDF_env) {
+  vec3 F0 = mix(vec3(0.04), albedo, metallic);
+  vec3  F = fresnel_schlick_roughness(F0, NdotV, roughness);
+  vec3 Kd = mix(vec3(1.0) - F, vec3(0.0), metallic);
+  vec3 diffuse = Kd * albedo * INV_PI * irradiance;
+  vec3 specular = prefiltered_env * (F * BRDF_env.x + BRDF_env.y);
+  return occlusion * (diffuse + specular);
+}
+
+void main()
+{
+  // TODO: Also use the specular F0 map from the model, and emissive. Make sure
+  // to use all maps.
+  // https://sketchfab.com/models/b81008d513954189a063ff901f7abfe4
+#ifdef HAS_NORMAL_MAP
+  vec3 normalMapSample = texture(NormalMap, Texcoord).xyz * 2.0 - 1.0;
+  vec3 N = get_ws_normal(Normal, normalMapSample);
+#elif HAS_NORMALS
+  vec3 N = normalize(Normal);
+#endif
+  vec3 V = normalize(CameraPosition - Position);
+  vec3 R = reflect(-V, N);
+  // Not needed for IBL.
+  //vec3 L = N;
+  //vec3 H = normalize(L + V);
+
+  float NdotV = max(0.0, dot(N, V));
+  // Not needed for IBL.
+  //float NdotL = max(0.0, dot(N,L));
+  //float NdotH = max(0.0, dot(N,H));
+  //float HdotV = clamp(dot(H,V), 0.0, 1.0);  // Clamp to prevent black spots.
+
+  // TODO: BaseColorFactor and BaseColorTexture are vec4/rgba quantities
+  // respectively. Handle the alpha channel.
+  // TODO: Other factors.
+#ifdef HAS_ALBEDO_MAP
+  vec3 albedo = vec3(BaseColorFactor) * texture(BaseColorTexture, Texcoord).rgb;
+#else
+  vec3 albedo = vec3(BaseColorFactor);
+#endif
+#ifdef HAS_METALLIC_ROUGHNESS_MAP
+  // Spec: "Its green channel contains roughness values and its blue channel
+  // contains metalness values."
+  vec2 metal_roughness
+    = vec2(MetallicFactor, RoughnessFactor)
+    * texture(MetallicRoughnessTexture, Texcoord).bg;
+#else
+  vec2 metal_roughness = vec2(MetallicFactor, RoughnessFactor);
+#endif
+#ifdef HAS_EMISSIVE_MAP
+  vec3 emissive = EmissiveFactor * texture(EmissiveTexture, Texcoord).rgb;
+#else
+  vec3 emissive = EmissiveFactor;
+#endif
+#ifdef HAS_OCCLUSION_MAP
+  float occlusion = texture(AmbientOcclusionTexture, Texcoord).r;
+#else
+  float occlusion = 1.0;
+#endif
+  float metallic  = metal_roughness.x;
+  float roughness = metal_roughness.y;
+
+  // For a single light direction:
+  // vec3 brdf = cook_torrance(albedo, metallic, roughness, NdotL, NdotV, NdotH, HdotV);
+  // vec3 Li = texture(Sky, N).rgb;
+  // vec3 colour = brdf * Li * NdotL;
+
+  // For IBL:
+  vec3 irradiance = texture(IrradianceMap, N).rgb;
+  vec3 prefiltered_env = textureLod(PrefilteredEnvironmentMap, R, roughness * MaxReflectionLOD).rgb;
+  vec2 BRDF_env = texture(BRDFIntegrationMap, vec2(NdotV, roughness)).rg;
+  vec3 colour = cook_torrance_IBL(
+    albedo, metallic, roughness, occlusion, NdotV, irradiance, prefiltered_env, BRDF_env);
+
+  colour += emissive;
+
+  // Reinhard tone mapping.
+  colour = colour / (colour + vec3(1.0));
+
+  // Gamma correction.
+  colour = pow(colour, vec3(1.0 / 2.2));
+
+  // Debugging.
+  //
+  // Normal texture.
+  //colour = normalMapSample * 0.5 + 0.5;
+  //
+  // Geometry normal.
+  //colour = normalize(Normal) * 0.5 + 0.5;
+  //
+  // Shading normal.
+  //colour = N * 0.5 + 0.5;
+  //
+  // Tangent and bitangent.
+  // {
+  //   vec3 pos_dx = dFdx(Position);
+  //   vec3 pos_dy = dFdy(Position);
+  //   // vec3 uv_dx = vec3(dFdx(Texcoord), 0.0);
+  //   // vec3 uv_dy = vec3(dFdy(Texcoord), 0.0);
+  //   vec3 uv_dx = dFdx(vec3(Texcoord, 0.0));
+  //   vec3 uv_dy = dFdy(vec3(Texcoord, 0.0));
+  //   vec3 T = (uv_dy.t * pos_dx - uv_dx.t * pos_dy) /
+  //            (uv_dx.s * uv_dy.t - uv_dy.s * uv_dx.t);
+  //   // vec3 T = pos_dx * uv_dy.t - pos_dy * uv_dx.t;
+  //   vec3 N = normalize(Normal);
+  //   T = normalize(T - dot(T, N) * N);
+  //   vec3 B = normalize(cross(N, T));
+
+  //   if (gl_FrontFacing == false) {
+  //     T = -T;
+  //     B = -B;
+  //     N = -N;
+  //   }
+
+  //   // Tangent.
+  //   //colour = T * 0.5 + 0.5;
+  //   // Bitangent.
+  //   //colour = B * 0.5 + 0.5;
+  // }
+
+  Colour = vec4(colour, 1.0);
+}
diff --git a/shaders/cook_torrance.vert b/shaders/cook_torrance.vert
new file mode 100644
index 0000000..5f126c0
--- /dev/null
+++ b/shaders/cook_torrance.vert
@@ -0,0 +1,75 @@
+precision highp float;
+
+uniform mat4 ModelMatrix;
+// uniform mat4 Modelview;
+uniform mat4 View;
+uniform mat4 Projection;
+//uniform mat4 MVP;
+#ifdef HAS_JOINTS
+// The client should pass in an appropriate value for MAX_JOINTS.
+// #define MAX_JOINTS 96
+//
+// matnxm -- n columns and m rows, different convention from math.
+// We don't need the last row of [0, 0, 0, 1], so drop it to pack the matrices
+// as tightly as possible.
+// 256 joints * 4x4 matrix * 4 bytes/float = 16.0KB
+// 256 joints * 4x3 matrix * 4 bytes/float = 12.0KB
+//  96 joints * 4x4 matrix * 4 bytes/float =  6.0KB
+//  96 joints * 4x3 matrix * 4 bytes/float =  4.5KB
+//uniform mat4x3 Joints[MAX_JOINTS];
+uniform mat4 JointMatrices[MAX_JOINTS]; // Use 4x4 for now to keep it simple.
+#endif
+
+layout (location = 0) in vec3 vPosition;
+#ifdef HAS_NORMALS
+layout (location = 1) in vec3 vNormal;
+#endif
+#ifdef HAS_TANGENTS
+layout (location = 2) in vec4 vTangent;
+#endif
+#ifdef HAS_TEXCOORDS
+layout (location = 3) in vec2 vTexcoord;
+#endif
+#ifdef HAS_JOINTS
+layout (location = 4) in uvec4 vJoint;
+layout (location = 5) in vec4  vWeight;
+#endif
+
+// World-space position, normal and tangent.
+out vec3 Position;
+#ifdef HAS_NORMALS
+out vec3 Normal;
+#endif
+#ifdef HAS_TANGENTS
+out vec4 Tangent;
+#endif
+#ifdef HAS_TEXCOORDS
+out vec2 Texcoord;
+#endif
+
+void main()
+{
+#ifdef HAS_JOINTS
+  mat4 skinMatrix =
+    vWeight.x * JointMatrices[vJoint.x] +
+    vWeight.y * JointMatrices[vJoint.y] +
+    vWeight.z * JointMatrices[vJoint.z] +
+    vWeight.w * JointMatrices[vJoint.w];
+  Position = vec3(ModelMatrix * skinMatrix * vec4(vPosition, 1.0));
+#else
+  Position = vec3(ModelMatrix * vec4(vPosition, 1.0));
+#endif
+#ifdef HAS_NORMALS
+  Normal = mat3(ModelMatrix) * vNormal;
+  //Normal = normalize(ModelMatrix * vec4(vNormal, 0.0)).xyz;
+#endif
+#ifdef HAS_TANGENTS
+  Tangent = vec4(mat3(ModelMatrix) * vTangent.xyz, vTangent.w);
+#endif
+#ifdef HAS_TEXCOORDS
+  Texcoord = vTexcoord;
+#endif
+  gl_Position = Projection * View * vec4(Position, 1.0);
+  //gl_Position = Projection * vec4(Position, 1.0);
+  //gl_Position = MVP * vec4(vPosition, 1.0);
+}
diff --git a/shaders/cubemap_filtering.vert b/shaders/cubemap_filtering.vert
new file mode 100644
index 0000000..d0cf73f
--- /dev/null
+++ b/shaders/cubemap_filtering.vert
@@ -0,0 +1,39 @@
+precision highp float;
+
+#define PI 3.1415926535897932384626433832795
+#define FOVY (90.0 * PI / 180.0)
+
+uniform mat4 CameraRotation; // From camera space to world space.
+uniform float Flip;
+
+layout (location = 0) in vec2 vPosition;
+
+out vec3 Ray;
+
+// DEBUG
+// out vec2 Texcoord;
+
+// This is very similar to the skyquad vertex shader.
+//
+// The ray is not normalized because it isn't necessary for cubemap sampling.
+//
+// We also use a fixed fovy = 90 degrees because we want the frustum to pass
+// exactly through each face of the cube. The aspect ratio is also just 1.
+vec3 sky_ray(vec2 FilmPosition)
+{
+  float d = 0.5 / tan(FOVY/2.0);
+  return vec3(FilmPosition, -d);
+}
+
+void main()
+{
+  vec2 FilmPosition = vPosition * 0.5; // map [-1,1] -> [-1/2, +1/2]
+  FilmPosition *= Flip;
+  Ray = mat3(CameraRotation) * sky_ray(FilmPosition);
+  // TODO: Should disable depth test when rendering.
+  gl_Position = vec4(vPosition, 0.99999, 1.0); // z=1 -> send to background
+
+  // DEBUG
+  // Texcoord   = FilmPosition + 0.5;
+  // Texcoord.y = 1.0 - Texcoord.y;
+}
diff --git a/shaders/debug3d.frag b/shaders/debug3d.frag
new file mode 100644
index 0000000..54568d4
--- /dev/null
+++ b/shaders/debug3d.frag
@@ -0,0 +1,21 @@
+precision highp float;
+
+const vec3 Colour = vec3(0.97, 0.948, 0.91);
+
+const vec3 ToLight = vec3(1, 0.7, 1);
+
+in vec3 Normal;
+
+out vec4 FragColour;
+
+void main()
+{
+    vec3 N = normalize(Normal);
+    vec3 L = normalize(ToLight);
+
+    vec3 a = vec3(0.7);
+    vec3 d = vec3(0.3 * (0.7*max(0.0, dot(L,N)) + 0.3*max(0.0, dot(-L,N))));
+    vec3 c = Colour * (a+d);
+
+    FragColour = vec4(pow(c, vec3(1.0 / 2.2)), 1.0);
+}
diff --git a/shaders/debug3d.vert b/shaders/debug3d.vert
new file mode 100644
index 0000000..d51684f
--- /dev/null
+++ b/shaders/debug3d.vert
@@ -0,0 +1,15 @@
+precision highp float;
+
+uniform mat4 Modelview;
+uniform mat4 Projection;
+
+layout (location = 0) in vec3 vPosition;
+layout (location = 1) in vec3 vNormal;
+
+out vec3 Normal;
+
+void main()
+{
+    Normal = mat3(Modelview) * vNormal;
+    gl_Position = Projection * Modelview * vec4(vPosition, 1.0);
+}
diff --git a/shaders/immediate_mode.frag b/shaders/immediate_mode.frag
new file mode 100644
index 0000000..ac23b5c
--- /dev/null
+++ b/shaders/immediate_mode.frag
@@ -0,0 +1,10 @@
+precision highp float;
+
+uniform vec4 Colour;
+
+out vec4 FragColour;
+
+void main()
+{
+  FragColour = vec4(pow(Colour.rgb, vec3(1.0/2.2)), Colour.a);
+}
diff --git a/shaders/immediate_mode.vert b/shaders/immediate_mode.vert
new file mode 100644
index 0000000..65070bb
--- /dev/null
+++ b/shaders/immediate_mode.vert
@@ -0,0 +1,11 @@
+precision highp float;
+
+uniform mat4 Model;
+uniform mat4 ViewProjection;
+
+layout (location = 0) in vec3 vPosition;
+
+void main()
+{
+  gl_Position = ViewProjection * Model * vec4(vPosition, 1.0);
+}
diff --git a/shaders/irradiance_map.frag b/shaders/irradiance_map.frag
new file mode 100644
index 0000000..8200e73
--- /dev/null
+++ b/shaders/irradiance_map.frag
@@ -0,0 +1,65 @@
+precision highp float;
+
+#define PI 3.1415926535897932384626433832795
+#define EPS 0.001
+#define NUM_SAMPLES_AZIMUTH 250
+#define NUM_SAMPLES_ZENITH 50
+#define MAX_AZIMUTH (2*PI)
+#define MAX_ZENITH (PI/2.0)
+#define AZIMUTH_DELTA (MAX_AZIMUTH / float(NUM_SAMPLES_AZIMUTH))
+#define ZENITH_DELTA (MAX_ZENITH / float(NUM_SAMPLES_ZENITH))
+
+uniform samplerCube Sky;
+
+in vec3 Ray;
+
+// DEBUG
+// in vec2 Texcoord;
+
+layout (location = 0) out vec4 Color;
+
+void main()
+{
+  // Tangent space:
+  //
+  //        N
+  //        |
+  //        |
+  //        |
+  //        |_ _ _ _ _ B
+  //       /
+  //      /
+  //     T
+  vec3 N = normalize(Ray);
+  vec3 B = (abs(N.x) - 1.0 <= EPS) ? vec3(0.0, 0.0, 1.0) : vec3(1.0, 0.0, 0.0);
+  vec3 T = normalize(cross(B, N));
+  B = normalize(cross(N, T));
+
+  int num_samples = 0;
+  vec3 irradiance = vec3(0.0);
+  for (float theta = 0.0; theta < MAX_AZIMUTH; theta += AZIMUTH_DELTA) {
+    for (float phi = 0.0; phi < MAX_ZENITH; phi += ZENITH_DELTA) {
+      // Spherical to Cartesian.
+      vec3 sample_tangent_space = vec3(
+        sin(phi) * cos(theta),
+        sin(phi) * sin(theta),
+        cos(phi));
+      // Tangent space to world space.
+      vec3 sample_world_space =
+        sample_tangent_space.x * B +
+        sample_tangent_space.y * T +
+        sample_tangent_space.z * N;
+
+      irradiance += texture(Sky, sample_world_space).rgb * sin(phi) * cos(phi);
+      num_samples += 1;
+    }
+  }
+  irradiance = PI * irradiance / float(num_samples);
+
+  // For debugging in trace.
+  //irradiance = texture(Sky, Ray).rgb;
+  // irradiance = vec3(Texcoord, 0.0);
+  //irradiance = pow(irradiance, vec3(1.0/2.2));
+
+  Color = vec4(irradiance, 1.0);
+}
diff --git a/shaders/prefiltered_environment_map.frag b/shaders/prefiltered_environment_map.frag
new file mode 100644
index 0000000..8327950
--- /dev/null
+++ b/shaders/prefiltered_environment_map.frag
@@ -0,0 +1,78 @@
+precision highp float;
+
+#define PI 3.1415926535897932384626433832795
+#define NUM_SAMPLES 4096
+
+uniform samplerCube Sky;
+uniform float Roughness;
+
+in vec3 Ray;
+
+layout (location = 0) out vec4 Color;
+
+float radical_inverse_VdC(uint bits) {
+    bits = (bits << 16u) | (bits >> 16u);
+    bits = ((bits & 0x55555555u) << 1u) | ((bits & 0xAAAAAAAAu) >> 1u);
+    bits = ((bits & 0x33333333u) << 2u) | ((bits & 0xCCCCCCCCu) >> 2u);
+    bits = ((bits & 0x0F0F0F0Fu) << 4u) | ((bits & 0xF0F0F0F0u) >> 4u);
+    bits = ((bits & 0x00FF00FFu) << 8u) | ((bits & 0xFF00FF00u) >> 8u);
+    return float(bits) * 2.3283064365386963e-10; // / 0x100000000
+}
+
+vec2 hammersley(uint i, uint N) {
+    return vec2(float(i)/float(N), radical_inverse_VdC(i));
+}
+
+vec3 importance_sample_GGX(vec2 sample_box, vec3 N, float roughness) {
+  float r2 = roughness * roughness;
+
+  // Spherical coordinates.
+  float phi = 2.0 * PI * sample_box.x;
+  float cos_theta = sqrt((1.0 - sample_box.y) / (1.0 + (r2*r2 - 1.0) * sample_box.y));
+  float sin_theta = sqrt(1.0 - cos_theta * cos_theta);
+
+  // Map spherical coordinates to Cartesian coordinates in tangent space.
+  vec3 H = vec3(cos(phi) * sin_theta, sin(phi) * sin_theta, cos_theta);
+
+  // Map from tangent space to world space.
+  //
+  // Tangent space:
+  //
+  //        N
+  //        |
+  //        |
+  //        |
+  //        |_ _ _ _ _ B
+  //       /
+  //      /
+  //     T
+  vec3 up = abs(N.z) < 0.999 ? vec3(0.0, 0.0, 1.0) : vec3(1.0, 0.0, 0.0);
+  vec3 T = normalize(cross(up,N));
+  vec3 B = cross(N,T);
+  vec3 H_ws = H.x*T + H.y*B + H.z*N;
+  return H_ws;
+}
+
+void main()
+{
+  vec3 N = normalize(Ray);
+  vec3 R = N;
+  vec3 V = R;
+
+  vec3 irradiance = vec3(0.0);
+  float total_weight = 0.0;
+  for (uint i = 0; i < NUM_SAMPLES; ++i) {
+    vec2 sample_box = hammersley(i, NUM_SAMPLES);
+    vec3 H = importance_sample_GGX(sample_box, N, Roughness);
+    vec3 L = reflect(-V,H);
+
+    float NdotL = max(dot(N,L), 0.0);
+    if (NdotL > 0.0) {
+      irradiance += texture(Sky, H).rgb * NdotL;
+      total_weight += NdotL;
+    }
+  }
+  irradiance /= total_weight;
+
+  Color = vec4(irradiance, 1.0);
+}
diff --git a/shaders/quad.vert b/shaders/quad.vert
new file mode 100644
index 0000000..ef1834c
--- /dev/null
+++ b/shaders/quad.vert
@@ -0,0 +1,9 @@
+layout (location = 0) in vec2 Position;  // Assuming Position in [-1,1].
+
+out vec2 Texcoord;
+
+void main()
+{
+  Texcoord = Position * 0.5 + 0.5;
+  gl_Position = vec4(Position, 0.0, 1.0);
+}
diff --git a/shaders/skyquad.frag b/shaders/skyquad.frag
new file mode 100644
index 0000000..9b44bfd
--- /dev/null
+++ b/shaders/skyquad.frag
@@ -0,0 +1,13 @@
+uniform samplerCube Skyquad;
+
+in vec3 Ray;
+
+layout (location = 0) out vec4 Colour;
+
+void main()
+{
+    vec3 R = normalize(Ray);
+    Colour = vec4(pow(texture(Skyquad, R).rgb, vec3(1.0/2.2)), 1.0);
+    // Debug.
+    //Colour = vec4(pow(R*0.5 + 0.5, vec3(1.0 / 2.2)), 1.0);
+}
diff --git a/shaders/skyquad.vert b/shaders/skyquad.vert
new file mode 100644
index 0000000..c0c46e6
--- /dev/null
+++ b/shaders/skyquad.vert
@@ -0,0 +1,27 @@
+uniform mat4  CameraRotation; // From camera space to world space.
+uniform float Fovy;
+uniform float Aspect;
+
+layout (location = 0) in vec2 Position;
+
+out vec3 Ray;
+
+// We would typically normalize the vector, but there is no need to do so when
+// sampling a cube map.
+vec3 sky_ray(vec2 FilmPosition)
+{
+  //float d = 0.5 / tan(Fovy/2.0);
+  // return vec3((FilmPosition.x - 0.5) * Aspect,
+  //              FilmPosition.y - 0.5,
+  //              -d);
+  float d = 0.5 / tan(Fovy/2.0);
+  return vec3(FilmPosition, -d);
+}
+
+void main()
+{
+  vec2 FilmPosition = Position * 0.5; // map [-1,1] -> [-1/2, +1/2]
+  Ray = mat3(CameraRotation) * sky_ray(FilmPosition);
+  // Set z to the background.
+  gl_Position = vec4(Position, 0.99999, 1.0); // z=1 -> send to background
+}
diff --git a/shaders/view_normal_mapped_normals.frag b/shaders/view_normal_mapped_normals.frag
new file mode 100644
index 0000000..a372c02
--- /dev/null
+++ b/shaders/view_normal_mapped_normals.frag
@@ -0,0 +1,28 @@
+precision highp float;
+
+uniform sampler2D NormalMap;
+
+in vec3 Normal;
+in vec4 Tangent;
+in vec3 Bitangent; // TODO: Compute here or in PS?
+in vec2 Texcoord;
+
+out vec4 FragColour;
+
+// TODO: Move to "normal.h"
+vec3 get_vs_normal(vec3 normal, vec4 tangent, vec3 normalMapSample) {
+  vec3 N = normal;
+  // vec3 T = normalize(interpTangent   - dot(tangent, N)*N);
+  // vec3 B = normalize(interpBitangent - dot(interpTangent, N)*N - dot(interpTangent, T)*T);
+  vec3 T = tangent.xyz;
+  //vec3 B = tangent.w * cross(N,T);
+  vec3 B = Bitangent;
+  vec3 n = normalMapSample;
+  return normalize(n.x*T + n.y*B + n.z*N);
+}
+
+void main() {
+  vec3 normalMapSample = texture(NormalMap, Texcoord).xyz * 2.0 - 1.0;
+  vec3 N = get_vs_normal(Normal, Tangent, normalMapSample);
+  FragColour = vec4(pow(N, vec3(1.0 / 2.2)), 1.0);
+}
diff --git a/shaders/view_normal_mapped_normals.vert b/shaders/view_normal_mapped_normals.vert
new file mode 100644
index 0000000..004ed9a
--- /dev/null
+++ b/shaders/view_normal_mapped_normals.vert
@@ -0,0 +1,22 @@
+precision highp float;
+
+uniform mat4 Modelview;
+uniform mat4 Projection;
+
+layout (location = 0) in vec3 vPosition;
+layout (location = 1) in vec3 vNormal;
+layout (location = 2) in vec4 vTangent;
+layout (location = 3) in vec2 vTexcoord;
+
+out vec3 Normal;
+out vec4 Tangent;
+out vec3 Bitangent; // TODO: Compute here or in PS?
+out vec2 Texcoord;
+
+void main() {
+  Texcoord = vTexcoord;
+  Normal = mat3(Modelview) * vNormal;
+  Tangent = vec4(mat3(Modelview) * vTangent.xyz, vTangent.w);
+  Bitangent = cross(Normal, Tangent.xyz) * vTangent.w;
+  gl_Position = Projection * Modelview * vec4(vPosition, 1.0);
+}
diff --git a/shaders/view_normals.frag b/shaders/view_normals.frag
new file mode 100644
index 0000000..e90189c
--- /dev/null
+++ b/shaders/view_normals.frag
@@ -0,0 +1,11 @@
+precision highp float;
+
+in vec3 Normal;
+
+out vec4 FragColour;
+
+void main()
+{
+    vec3 N = normalize(Normal);
+    FragColour = vec4(pow(N, vec3(1.0 / 2.2)), 1.0);
+}
diff --git a/shaders/view_normals.vert b/shaders/view_normals.vert
new file mode 100644
index 0000000..d51684f
--- /dev/null
+++ b/shaders/view_normals.vert
@@ -0,0 +1,15 @@
+precision highp float;
+
+uniform mat4 Modelview;
+uniform mat4 Projection;
+
+layout (location = 0) in vec3 vPosition;
+layout (location = 1) in vec3 vNormal;
+
+out vec3 Normal;
+
+void main()
+{
+    Normal = mat3(Modelview) * vNormal;
+    gl_Position = Projection * Modelview * vec4(vPosition, 1.0);
+}
diff --git a/shaders/view_tangents.frag b/shaders/view_tangents.frag
new file mode 100644
index 0000000..11d1455
--- /dev/null
+++ b/shaders/view_tangents.frag
@@ -0,0 +1,17 @@
+precision highp float;
+
+in vec4 Tangent;
+
+out vec4 FragColour;
+
+void main() {
+  vec3 T = normalize(Tangent.xyz);
+  FragColour = vec4(pow(T, vec3(1.0 / 2.2)), 1.0);FragColour = vec4(pow(T, vec3(1.0 / 2.2)), 1.0);
+
+  // View sign.
+  // float sign = Tangent.w;
+  // float R = sign > 0.0 ? 1.0 : 0.0;
+  // float B = sign < 0.0 ? 1.0 : 0.0;
+  // vec3 signColour = vec3(R,0.0,B);
+  // FragColour = vec4(pow(signColour, vec3(1.0 / 2.2)), 1.0);
+}
diff --git a/shaders/view_tangents.vert b/shaders/view_tangents.vert
new file mode 100644
index 0000000..561ad22
--- /dev/null
+++ b/shaders/view_tangents.vert
@@ -0,0 +1,14 @@
+precision highp float;
+
+uniform mat4 Modelview;
+uniform mat4 Projection;
+
+layout (location = 0) in vec3 vPosition;
+layout (location = 2) in vec4 vTangent;
+
+out vec4 Tangent;
+
+void main() {
+  Tangent = vec4(Tangent.xyz = mat3(Modelview) * vTangent.xyz, vTangent.w);
+  gl_Position = Projection * Modelview * vec4(vPosition, 1.0);
+}
diff --git a/shaders/view_texture.frag b/shaders/view_texture.frag
new file mode 100644
index 0000000..12fa367
--- /dev/null
+++ b/shaders/view_texture.frag
@@ -0,0 +1,15 @@
+uniform sampler2D Texture;
+
+in vec2 Texcoord;
+
+layout (location = 0) out vec4 Colour;
+
+void main()
+{
+    // There is a question here whether we want to view the texture through the
+    // sampler or unfiltered. Prefer the latter for now.
+    //vec3 colour = texture(Texture, Texcoord).rgb;
+    ivec2 st = ivec2(Texcoord * vec2(textureSize(Texture, 0)));
+    vec3 colour = texelFetch(Texture, st, 0).rgb;
+    Colour = vec4(pow(colour, vec3(1.0 / 2.2)), 1.0);
+}
diff --git a/shaders/view_texture.vert b/shaders/view_texture.vert
new file mode 100644
index 0000000..4e3c7d7
--- /dev/null
+++ b/shaders/view_texture.vert
@@ -0,0 +1,13 @@
+layout (location = 0) in vec2 Position;
+
+out vec2 Texcoord;
+
+void main()
+{
+    Texcoord = Position * vec2(0.5) + vec2(0.5);// Map from [-1, +1] to [0, 1].
+    // The Gfx library is written to work with the glTF sample models, which
+    // seem to want the textures loaded "as is" without flipping. Flip the
+    // y-coordinate here so that the texture appears as expected.
+    Texcoord.y = 1.0 - Texcoord.y;
+    gl_Position = vec4(Position, 0.0, 1.0);
+}