rt: add reflections

i was trying to add specular properly: replace them with specular bounce. but it doesn't really work that easily. need some kind of color mapping and figuring out how to make them look consistent.

this commit still does them separately, i.e. specular is done in direct lighting pass. no emissive is added on bounce. this probably makes it not reflect skybox ;_;.

ref_vk/shaders/bounce.comp

@@ -17,6 +17,7 @@ RAY_LIGHT_DIRECT_INPUTS(X)
 #undef X
 
 layout(set=0, binding=20, rgba16f) uniform writeonly image2D out_indirect_diffuse;
+layout(set=0, binding=21, rgba16f) uniform writeonly image2D out_indirect_specular;
 
 #include "ray_primary_common.glsl"
 #include "ray_primary_hit.glsl"
@@ -33,8 +34,8 @@ layout(set=0, binding=20, rgba16f) uniform writeonly image2D out_indirect_diffus
 #undef PAYLOAD_LOCATION_SHADOW
 #define PAYLOAD_LOCATION_SHADOW 0
 
-#define BINDING_LIGHTS 7
-#define BINDING_LIGHT_CLUSTERS 8
+#define BINDING_LIGHTS 19
+#define BINDING_LIGHT_CLUSTERS 18
 #include "light.glsl"
 
 void readNormals(ivec2 uv, out vec3 geometry_normal, out vec3 shading_normal) {
@@ -83,7 +84,10 @@ bool getHit(vec3 origin, vec3 direction, inout RayPayloadPrimary payload) {
 	return true;
 }
 
-vec3 computeBounce(ivec2 pix, vec3 direction) {
+void computeBounce(ivec2 pix, vec3 direction, out vec3 diffuse, out vec3 specular) {
+	diffuse = vec3(0.);
+	specular = vec3(0.);
+
 	const vec4 material_data = imageLoad(material_rmxx, pix);
 
 	MaterialProperties material;
@@ -102,30 +106,42 @@ vec3 computeBounce(ivec2 pix, vec3 direction) {
 	// 1. Make a "random" material-based ray for diffuse lighting
 	vec3 bounce_direction = vec3(0.);
 	vec3 brdf_weight = vec3(0.);
-	const int brdf_type = DIFFUSE_TYPE;
-	//const int brdf_type = SPECULAR_TYPE; // FIXME test
+	int brdf_type = DIFFUSE_TYPE;
+
+	if (material.metalness == 1.0f && material.roughness == 0.0f) {
+		// Fast path for mirrors
+		brdf_type = SPECULAR_TYPE;
+	} else {
+		// Decide whether to sample diffuse or specular BRDF (based on Fresnel term)
+		const float brdf_probability = getBrdfProbability(material, -direction, shading_normal);
+		if (rand01() < brdf_probability) {
+			brdf_type = SPECULAR_TYPE;
+			throughput /= brdf_probability;
+		}
+	}
 	const vec2 u = vec2(rand01(), rand01());
 	if (!evalIndirectCombinedBRDF(u, shading_normal, geometry_normal, -direction, material, brdf_type, bounce_direction, brdf_weight))
-		return vec3(0.);//vec3(1., 0., 0.);
+		return;
 
 	const float throughput_threshold = 1e-3;
 	throughput *= brdf_weight;
 	if (dot(throughput, throughput) < throughput_threshold)
-		return vec3(0.);//, 1., 0.);
+		return;
 
 	// 2. Rake yuri it, get hit
 	// 3. Get relevant Geometry data
 	RayPayloadPrimary payload;
 	payload.base_color_a = vec4(0.);
+	payload.emissive = vec4(0.);
 	if (!getHit(pos, bounce_direction, payload))
-		return vec3(0.);//, 0., 1.);
+		return;
 
 	throughput *= payload.base_color_a.rgb;
 
 	// 4. Sample light sources
-	vec3 diffuse = vec3(0.);
 	{
-		vec3 specular = vec3(0.);
+		vec3 ldiffuse = vec3(0.);
+		vec3 lspecular = vec3(0.);
 		const vec3 hit_pos = payload.hit_t.xyz;
 		const vec3 hit_shading_normal = normalDecode(payload.normals_gs.zw);
 
@@ -134,10 +150,15 @@ vec3 computeBounce(ivec2 pix, vec3 direction) {
 		hit_material.emissive = vec3(0.f);
 		hit_material.metalness = payload.material_rmxx.g;
 		hit_material.roughness = payload.material_rmxx.r;
-		computeLighting(hit_pos, hit_shading_normal, throughput, -bounce_direction, hit_material, diffuse, specular);
-	}
+		computeLighting(hit_pos, hit_shading_normal, throughput, -bounce_direction, hit_material, ldiffuse, lspecular);
 
-	return diffuse;
+		const vec3 final_color = ldiffuse + lspecular;
+
+		if (brdf_type == DIFFUSE_TYPE)
+			diffuse += final_color;
+		else
+			specular += final_color;// + payload.emissive.rgb * 75;
+	}
 }
 
 void main() {
@@ -154,6 +175,8 @@ void main() {
 
 	rand01_state = ubo.ubo.random_seed + pix.x * 1833 + pix.y * 31337 + 12;
 
-	const vec3 diffuse = computeBounce(pix, direction);
+	vec3 diffuse, specular;
+	computeBounce(pix, direction, diffuse, specular);
 	imageStore(out_indirect_diffuse, pix, vec4(diffuse, 0.f));
+	imageStore(out_indirect_specular, pix, vec4(specular, 0.f));
 }

ref_vk/shaders/denoiser.comp

@@ -29,6 +29,7 @@ layout(set = 0, binding = 10, rgba32f) uniform readonly image2D geometry_prev_po
 layout(set = 0, binding = 11) uniform UBO { UniformBuffer ubo; } ubo;
 
 layout(set = 0, binding = 12, rgba16f) uniform readonly image2D indirect_diffuse;
+layout(set = 0, binding = 13, rgba16f) uniform readonly image2D indirect_specular;
 
 //layout(set = 0, binding = 2, rgba16f) uniform readonly image2D light_poly_diffuse;
 /* layout(set = 0, binding = 3, rgba16f) uniform readonly image2D specular; */
@@ -159,6 +160,7 @@ void main() {
 			vec3 specular = vec3(0.);
 			specular += imageLoad(light_poly_specular, p).rgb;
 			specular += imageLoad(light_point_specular, p).rgb;
+			specular += imageLoad(indirect_specular, p).rgb;
 
 			{
 				const float sigma = KERNEL_SIZE / 2.;