From 24a7295dccfd559501753950509964869f88bec1 Mon Sep 17 00:00:00 2001
From: Kenneth Graunke <kenneth@whitecape.org>
Date: Wed, 27 Oct 2010 20:52:34 -0700
Subject: Convert shaders to work in surface space rather than eye space.

---
 src/phong.frag | 21 +++++++++------------
 src/phong.vert | 25 ++++++++++++++++++-------
 2 files changed, 27 insertions(+), 19 deletions(-)

diff --git a/src/phong.frag b/src/phong.frag
index 95eaaa7..a43a61d 100755
--- a/src/phong.frag
+++ b/src/phong.frag
@@ -1,23 +1,20 @@
-varying vec4 normal_es;
-varying vec4 position_es;
+varying vec3 light_ss;
+varying vec3 eye_ss;
 
 const vec4 diffuse_color = vec4(1.0, 0.0, 0.0, 1.0);
+
 /* Specular exponent.
  */
 uniform float s;
 
-/* Position of the light in eye-space.
- */
-const vec4 light_es = vec4(0.0, 3.0, 0.0, 1.0);
-
 void main(void)
 {
-	vec3 l = normalize((light_es - position_es).xyz);
-	vec3 v = normalize(-position_es.xyz);
+	vec3 l = normalize(light_ss);
+	vec3 v = normalize(eye_ss);
 	vec3 h = normalize(l + v);
-	float n_dot_l = dot(normal_es.xyz, l);
-	vec4 diff = diffuse_color * n_dot_l;
-	float spec = pow(dot(normal_es.xyz, h), s);
+	vec3 n = vec3(0, 0, 1);
+	vec4 diff = diffuse_color * dot(n, l);
+	float spec = pow(dot(n, h), s);
 
-	gl_FragColor = step(0.0, n_dot_l) * vec4(diff.xyz + vec3(spec), 1.0);
+	gl_FragColor = step(0.0, dot(n, l)) * vec4(diff.xyz + vec3(spec), 1.0);
 }
diff --git a/src/phong.vert b/src/phong.vert
index 26f6b25..a0c1fab 100755
--- a/src/phong.vert
+++ b/src/phong.vert
@@ -2,20 +2,31 @@ uniform mat4 mvp;
 uniform mat4 mv;
 
 attribute vec4 normal;
+attribute vec4 tangent;
 attribute vec2 uv;
 
-/* Normal transformed to eye space.
- */
-varying vec4 normal_es;
+// Vector from the light to the vertex transformed to surface space.
+varying vec3 light_ss;
+
+// ???
+varying vec3 eye_ss;
 
-/* Vertex position transformed to eye space.
+/* Position of the light in eye-space.
  */
-varying vec4 position_es;
+const vec3 light_pos_es = vec3(0.0, 3.0, 0.0);
 
 void main(void)
 {
 	gl_Position = mvp * gl_Vertex;
 
-	normal_es = mv * normal;
-	position_es = mv * gl_Vertex;
+	vec3 tangent_es = vec3(mv * tangent);
+	vec3 normal_es = vec3(mv * normal);
+	vec3 bitangent_es = cross(normal_es, tangent_es);
+	mat3 tbn = mat3(tangent_es, bitangent_es, normal_es);
+
+	vec3 vertex_pos_es = vec3(mv * gl_Vertex);
+	vec3 light_direction_es = light_pos_es - vertex_pos_es;
+
+	light_ss = normalize(light_direction_es * tbn);
+	eye_ss = -normalize(vertex_pos_es * tbn);
 }
-- 
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