From 4d276c9b986b111611b8396f94dae56dbe736387 Mon Sep 17 00:00:00 2001
From: Mikko Rasa <tdb@tdb.fi>
Date: Sat, 9 Oct 2021 20:47:39 +0300
Subject: [PATCH] Some refactoring of light calculations in shaders

---
 shaderlib/common.glsl       | 12 ++++++++++--
 shaderlib/cooktorrance.glsl |  8 ++++----
 shaderlib/phong.glsl        | 10 +++++-----
 3 files changed, 19 insertions(+), 11 deletions(-)

diff --git a/shaderlib/common.glsl b/shaderlib/common.glsl
index dde09c12..4d6112d9 100644
--- a/shaderlib/common.glsl
+++ b/shaderlib/common.glsl
@@ -71,6 +71,12 @@ void main()
 }
 
 #pragma MSP stage(fragment)
+struct IncomingLight
+{
+	vec3 direction;
+	vec3 color;
+};
+
 virtual vec3 get_fragment_normal()
 {
 	if(use_normal_map)
@@ -79,10 +85,12 @@ virtual vec3 get_fragment_normal()
 		return normalize(world_normal);
 }
 
-virtual vec3 get_light_direction(int index)
+virtual IncomingLight get_incoming_light(int index, vec3 world_pos)
 {
 	vec4 light_pos = light_sources[index].position;
-	return normalize(light_pos.xyz-world_vertex.xyz*light_pos.w);
+	vec3 rel_pos = light_pos.xyz-world_pos*light_pos.w;
+	float d = length(rel_pos);
+	return IncomingLight(rel_pos/d, light_sources[index].color);
 }
 
 virtual vec3 get_environment_sample(vec3 direction, float roughness)
diff --git a/shaderlib/cooktorrance.glsl b/shaderlib/cooktorrance.glsl
index f441a6d3..79f88f64 100644
--- a/shaderlib/cooktorrance.glsl
+++ b/shaderlib/cooktorrance.glsl
@@ -118,7 +118,7 @@ vec3 fresnel_schlick(vec3 halfway, vec3 look, vec3 base_color, float metalness)
 }
 
 /* Computes the full contribution of a single light */
-vec3 cooktorrance_one_light_direct(vec3 normal, vec3 look, vec3 light, vec3 light_color, vec3 base_color, float metalness, float roughness)
+vec3 cooktorrance_one_light_direct(vec3 normal, vec3 look, vec3 light, vec3 base_color, float metalness, float roughness)
 {
 	vec3 halfway = normalize(light-look);
 	float ndist = normal_distribution_ggxtr(normal, halfway, roughness);
@@ -128,7 +128,7 @@ vec3 cooktorrance_one_light_direct(vec3 normal, vec3 look, vec3 light, vec3 ligh
 	vec3 k_diff = (1.0-k_spec)*(1.0-metalness);
 
 	float spec_denom = max(4.0*max(dot(normal, -look), 0.0)*max(dot(normal, light), 0.0), 0.001);
-	return max(dot(normal, light), 0.0)*light_color*(k_diff*lambert_diffuse(base_color)+k_spec*ndist*geom/spec_denom);
+	return max(dot(normal, light), 0.0)*(k_diff*lambert_diffuse(base_color)+k_spec*ndist*geom/spec_denom);
 }
 
 vec3 cooktorrance_environment(vec3 normal, vec3 look, vec3 base_color, float metalness, float roughness)
@@ -155,9 +155,9 @@ vec3 cooktorrance_lighting(vec3 normal, vec3 look, vec3 base_color, float metaln
 	for(int i=0; i<max_lights; ++i)
 		if(light_sources[i].type!=0)
 		{
-			vec3 light = get_light_direction(i);
+			IncomingLight incoming = get_incoming_light(i, world_vertex.xyz);
 			float shadow = get_shadow_factor(i);
-			color += cooktorrance_one_light_direct(normal, look, light, light_sources[i].color, base_color, metalness, roughness)*shadow;
+			color += cooktorrance_one_light_direct(normal, look, incoming.direction, base_color, metalness, roughness)*incoming.color*shadow;
 		}
 
 	color += cooktorrance_environment(normal, look, base_color, metalness, roughness);
diff --git a/shaderlib/phong.glsl b/shaderlib/phong.glsl
index 004232ac..ed091ce9 100644
--- a/shaderlib/phong.glsl
+++ b/shaderlib/phong.glsl
@@ -79,15 +79,15 @@ vec3 phong_ambient(vec3 surface_diffuse)
 	return ambient_color.rgb*surface_diffuse;
 }
 
-vec3 phong_one_light(vec3 light, vec3 normal, vec3 look, vec3 light_color, vec3 surface_diffuse, vec3 surface_specular, float shininess)
+vec3 phong_one_light(vec3 light, vec3 normal, vec3 look, vec3 surface_diffuse, vec3 surface_specular, float shininess)
 {
 	float diffuse_intensity = max(dot(light, normal), 0.0);
-	vec3 color = light_color*surface_diffuse*diffuse_intensity;
+	vec3 color = surface_diffuse*diffuse_intensity;
 	if(use_specular)
 	{
 		vec3 reflected = reflect(look, normal);
 		float specular_intensity = pow(max(dot(reflected, light), 0.0), shininess);
-		color += light_color*surface_specular*specular_intensity;
+		color += surface_specular*specular_intensity;
 	}
 	return color;
 }
@@ -98,9 +98,9 @@ vec3 phong_lighting(vec3 normal, vec3 look, vec3 surface_diffuse, vec3 surface_s
 	for(int i=0; i<max_lights; ++i)
 		if(light_sources[i].type!=0)
 		{
-			vec3 light = get_light_direction(i);
+			IncomingLight incoming = get_incoming_light(i, world_vertex.xyz);
 			float shadow = get_shadow_factor(i);
-			color += phong_one_light(light, normal, look, light_sources[i].color, surface_diffuse, surface_specular, shininess)*shadow;
+			color += phong_one_light(incoming.direction, normal, look, surface_diffuse, surface_specular, shininess)*incoming.color*shadow;
 		}
 
 	if(use_emission)
-- 
2.45.2