pbr: various shader optimizations

resources/00-taisei.pkgdir/shader/pbr.frag.glsl

@@ -17,15 +17,14 @@ UNIFORM(13) vec3 light_colors[MAX_LIGHT_COUNT]; // layout-id also depends on MAX
 
 
 // taken from https://learnopengl.com/PBR/Lighting
-float distribution_ggx(vec3 n, vec3 h, float roughness) {
+float distribution_ggx(float ndoth, float roughness) {
 	float a = roughness*roughness;
 
 	float a2 = a*a;
-	float ndoth = max(dot(n, h), 0.0);
 	float ndoth2 = ndoth*ndoth;
 
 	float num = a2;
-	float denom = (ndoth2 * (a2 - 1.0) + 1.0);
+	float denom = ndoth2 * (a2 - 1.0) + 1.0;
 	denom = pi * denom * denom;
 
 	return num / denom;
@@ -33,17 +32,15 @@ float distribution_ggx(vec3 n, vec3 h, float roughness) {
 
 float geometry_schlick_ggx(float ndotv, float roughness) {
 	float r = (roughness + 1.0);
-	float k = (r*r) / 8.0;
+	float k = r * r * 0.125;
 
 	float num   = ndotv;
-	float denom = ndotv * (1.0 - k) + k;
+	float denom = mix(ndotv, 1, k);
 
 	return num / denom;
 }
 
-float geometry_smith(vec3 n, vec3 v, vec3 l, float roughness) {
-	float ndotv = max(dot(n, v), 0.0);
-	float ndotl = max(dot(n, l), 0.0);
+float geometry_smith(float ndotv, float ndotl, float roughness) {
 	float ggx2 = geometry_schlick_ggx(ndotv, roughness);
 	float ggx1 = geometry_schlick_ggx(ndotl, roughness);
 
@@ -51,47 +48,59 @@ float geometry_smith(vec3 n, vec3 v, vec3 l, float roughness) {
 }
 
 vec3 fresnel_schlick(float cosTheta, vec3 F0) {
-    return F0 + (1.0 - F0) * pow(1.0 - cosTheta, 5.0);
+	float x = 1.0 - cosTheta;
+	float x2 = (x * x);
+	float x5 = x2 * x2 * x;
+
+    return mix(vec3(x5), vec3(1.0), F0);
 }
 
 void main(void) {
-	vec3 albedo = (r_color * texture(tex, texCoord)).rgb;
-	float roughness = texture(roughness_map, texCoord).r;
-	vec3 tbn_normal = sample_normalmap(normal_map, texCoord);
-	vec3 ambient = texture(ambient_map, texCoord).rgb;
+	vec4 roughness_sample = texture(roughness_map, texCoord);
+	float alpha = roughness_sample.a;
 
-	float alpha = texture(roughness_map,texCoord).a;
 	if(alpha < 0.3) {
 		discard;
 	}
 
+	vec3 albedo = (r_color * texture(tex, texCoord)).rgb;
+	float roughness = roughness_sample.r;
+	vec3 tbn_normal = sample_normalmap(normal_map, texCoord);
+	vec3 ambient = texture(ambient_map, texCoord).rgb;
+
 	vec3 n = normalize(mat3(normalize(tangent), normalize(bitangent), normalize(normal))*tbn_normal);
 	vec3 v = normalize(-pos);
+	float NdotV = max(dot(n, v), 0.0);
 
-	vec3 F0 = vec3(0.04);
-	F0 = mix(F0, albedo, metallic);
+	vec3 F0 = mix(vec3(0.04), albedo, metallic);
+
+	float one_minus_metallic = 1.0 - metallic;
+	const float inverse_pi = 1.0 / pi;
 
 	vec3 Lo = vec3(0.0);
 	for(int i = 0; i < light_count; ++i) {
-		vec3 l = normalize(light_positions[i] - pos);
-		vec3 h = normalize(v + l);
-		float distance = length(light_positions[i] - pos);
-		float attenuation = 1 / (distance * distance);
-		vec3 radiance = light_colors[i] * attenuation;
+		vec3 cam_to_light = light_positions[i] - pos;
 
-		float NDF = distribution_ggx(n, h, roughness);
-		float G = geometry_smith(n, v, l, roughness);
-		vec3 F = fresnel_schlick(max(dot(h, v), 0.0), F0);
+		vec3 l = normalize(cam_to_light);
+		vec3 h = normalize(v + l);
+		vec3 radiance = light_colors[i] / dot(cam_to_light, cam_to_light);
+
+		float NdotL = max(dot(n, l), 0.0);
+		float NdotH = max(dot(n, h), 0.0);
+		float HdotV = max(dot(h, v), 0.0);
+
+		float NDF = distribution_ggx(NdotH, roughness);
+		float G = geometry_smith(NdotV, NdotL, roughness);
+		vec3 F = fresnel_schlick(HdotV, F0);
 
 		vec3 kS = F;
-		vec3 kD = vec3(1.0) - kS;
-		kD *= 1.0 - metallic;
+		vec3 kD = (1.0 - kS) * one_minus_metallic;
 
 		vec3 numerator = NDF * G * F;
-		float denominator = 4.0 * max(dot(n, v), 0.0) * max(dot(n, l), 0.0);
+		float denominator = 4.0 * NdotV * NdotL;
 		vec3 specular = numerator / max(denominator, 0.001);
-		float NdotL = max(dot(n, l), 0.0);
-		Lo += (kD * albedo / pi + specular) * radiance * NdotL;
+
+		Lo += (kD * albedo * inverse_pi + specular) * radiance * NdotL;
 	}
 
 	//vec3 ambient = vec3(0.03) * albedo * ao;