Eevee: Replace Cubemaps by octahedron maps for env. probes.

This enables us to use 2D texture arrays for multiple probes.
There is a little artifact with very high roughness caused elongated pixel due to the projection (along every 90° meridian).

2 files changed, 79 insertions, 17 deletions

diff --git a/source/blender/draw/engines/eevee/shaders/lit_surface_frag.glsl b/source/blender/draw/engines/eevee/shaders/lit_surface_frag.glsl
index bff7c05537a..ca3cec62bdb 100644
--- a/source/blender/draw/engines/eevee/shaders/lit_surface_frag.glsl
+++ b/source/blender/draw/engines/eevee/shaders/lit_surface_frag.glsl
@@ -4,7 +4,7 @@ uniform vec3 cameraPos;
 uniform vec3 eye;
 uniform mat4 ProjectionMatrix;
 
-uniform samplerCube probeFiltered;
+uniform sampler2D probeFiltered;
 uniform float lodMax;
 uniform vec3 shCoefs[9];
 
@@ -42,6 +42,44 @@ in vec3 viewNormal;
 #define HEMI     3.0
 #define AREA     4.0
 
+vec2 mapping_octahedron(vec3 cubevec, vec2 texel_size)
+{
+	/* projection onto octahedron */
+	cubevec /= dot( vec3(1), abs(cubevec) );
+
+	/* out-folding of the downward faces */
+	if ( cubevec.z < 0.0 ) {
+		cubevec.xy = (1.0 - abs(cubevec.yx)) * sign(cubevec.xy);
+	}
+
+	/* mapping to [0;1]ˆ2 texture space */
+	vec2 uvs = cubevec.xy * (0.5) + 0.5;
+
+	/* edge filtering fix */
+	uvs *= 1.0 - 2.0 * texel_size;
+	uvs += texel_size;
+
+	return uvs;
+}
+
+vec4 textureLod_octahedron(sampler2D tex, vec3 cubevec, float lod)
+{
+	vec2 texelSize = 1.0 / vec2(textureSize(tex, int(lodMax)));
+
+	vec2 uvs = mapping_octahedron(cubevec, texelSize);
+
+	return textureLod(tex, uvs, lod);
+}
+
+vec4 texture_octahedron(sampler2DArray tex, vec4 cubevec)
+{
+	vec2 texelSize = 1.0 / vec2(textureSize(tex, 0));
+
+	vec2 uvs = mapping_octahedron(cubevec.xyz, texelSize);
+
+	return texture(tex, vec3(uvs, cubevec.w));
+}
+
 void light_shade(
         LightData ld, ShadingData sd, vec3 albedo, float roughness, vec3 f0,
         out vec3 diffuse, out vec3 specular)
@@ -139,20 +177,7 @@ void light_visibility(LightData ld, ShadingData sd, out float vis)
 		vec3 cubevec = sd.W - ld.l_position;
 		float dist = length(cubevec);
 
-		/* projection onto octahedron */
-		cubevec /= dot( vec3(1), abs(cubevec) );
-
-		/* out-folding of the downward faces */
-		if ( cubevec.z < 0.0 ) {
-			cubevec.xy = (1.0 - abs(cubevec.yx)) * sign(cubevec.xy);
-		}
-		vec2 texelSize = vec2(1.0 / 512.0);
-
-		/* mapping to [0;1]ˆ2 texture space */
-		vec2 uvs = cubevec.xy * (0.5) + 0.5;
-		uvs = uvs * (1.0 - 2.0 * texelSize) + 1.0 * texelSize; /* edge filtering fix */
-
-		float z = texture(shadowCubes, vec3(uvs, shid)).r;
+		float z = texture_octahedron(shadowCubes, vec4(cubevec, shid)).r;
 
 		float esm_test = min(1.0, exp(-5.0 * dist) * z);
 		float sh_test = step(0, z - dist);
@@ -194,7 +219,7 @@ vec3 eevee_surface_lit(vec3 world_normal, vec3 albedo, vec3 f0, float roughness,
 	/* Envmaps */
 	vec2 uv = lut_coords(dot(sd.N, sd.V), roughness);
 	vec3 brdf_lut = texture(brdfLut, uv).rgb;
-	vec3 Li = textureLod(probeFiltered, spec_dir, roughness * lodMax).rgb;
+	vec3 Li = textureLod_octahedron(probeFiltered, spec_dir, roughness * lodMax).rgb;
 	indirect_radiance += Li * F_ibl(f0, brdf_lut.rg);
 	indirect_radiance += spherical_harmonics(sd.N, shCoefs) * albedo;
 
diff --git a/source/blender/draw/engines/eevee/shaders/probe_filter_frag.glsl b/source/blender/draw/engines/eevee/shaders/probe_filter_frag.glsl
index bee674e3e76..33714c5293c 100644
--- a/source/blender/draw/engines/eevee/shaders/probe_filter_frag.glsl
+++ b/source/blender/draw/engines/eevee/shaders/probe_filter_frag.glsl
@@ -1,17 +1,54 @@
 
 uniform samplerCube probeHdr;
 uniform float roughnessSquared;
+uniform float texelSize;
 uniform float lodFactor;
 uniform float lodMax;
+uniform float paddingSize;
 
 in vec3 worldPosition;
 
 out vec4 FragColor;
 
+vec3 octahedral_to_cubemap_proj(vec2 co)
+{
+	co = co * 2.0 - 1.0;
+
+	vec2 abs_co = abs(co);
+	vec3 v = vec3(co, 1.0 - (abs_co.x + abs_co.y));
+
+	if ( abs_co.x + abs_co.y > 1.0 ) {
+		v.xy = (abs(co.yx) - 1.0) * -sign(co.xy);
+	}
+
+	return v;
+}
+
 void main() {
+	vec2 uvs = gl_FragCoord.xy * texelSize;
+
+	/* Add a N pixel border to ensure filtering is correct
+	 * for N mipmap levels. */
+	uvs += uvs * texelSize * paddingSize * 2.0;
+	uvs -= texelSize * paddingSize;
+
+	/* edge mirroring : only mirror if directly adjacent
+	 * (not diagonally adjacent) */
+	vec2 m = abs(uvs - 0.5) + 0.5;
+	vec2 f = floor(m);
+	if (f.x - f.y != 0.0) {
+		uvs = 1.0 - uvs;
+	}
+
+	/* clamp to [0-1] */
+	uvs = fract(uvs);
+
+	/* get cubemap vector */
+	vec3 cubevec = octahedral_to_cubemap_proj(uvs);
+
 	vec3 N, T, B, V;
 
-	vec3 R = normalize(worldPosition);
+	vec3 R = normalize(cubevec);
 
 	/* Isotropic assumption */
 	N = V = R;