Implement a procedular bump map.

Based off the example shader in the Orange Book, 3rd ed., chapter 11.

2 files changed, 29 insertions, 4 deletions

diff --git a/src/phong.frag b/src/phong.frag
index a43a61d..0d53e85 100755
--- a/src/phong.frag
+++ b/src/phong.frag
@@ -1,20 +1,43 @@
 varying vec3 light_ss;
 varying vec3 eye_ss;
+varying vec2 uv_coord;
 
-const vec4 diffuse_color = vec4(1.0, 0.0, 0.0, 1.0);
+const vec3 base_color = vec3(1.0, 0.0, 0.0);
 
 /* Specular exponent.
  */
 uniform float s;
 
+/* Adapted from the Orange Book, 3rd edition, chapter 11. */
+vec3 perturbed_normal()
+{
+	const float BumpDensity = 30.0;
+	const float BumpSize = 0.15;
+
+	/* The incoming texture coordinate (uv_coord) ranges from 0 to 1.
+	 * Multiplying by BumpDensity gives coordinates between 0 and 30.
+	 * Then, fract gives us a value from 0 to 1...and subtracting 0.5
+	 * gives us a perturbation value between -0.5 and 0.5.
+	 */
+	vec2 c = BumpDensity * uv_coord;
+	vec2 p = fract(c) - vec2(0.5);
+
+	/* If not in a bump, return an unperturbed normal */
+	if (dot(p,p) >= BumpSize)
+		return vec3(0,0,1);
+
+	/* Otherwise, return the perturbed normal */
+	return normalize(vec3(p, 1));
+}
+
 void main(void)
 {
 	vec3 l = normalize(light_ss);
 	vec3 v = normalize(eye_ss);
 	vec3 h = normalize(l + v);
-	vec3 n = vec3(0, 0, 1);
-	vec4 diff = diffuse_color * dot(n, l);
+	vec3 n = perturbed_normal();
+	vec3 diff = base_color * dot(n, l);
 	float spec = pow(dot(n, h), s);
 
-	gl_FragColor = step(0.0, dot(n, l)) * vec4(diff.xyz + vec3(spec), 1.0);
+	gl_FragColor = step(0.0, dot(n, l)) * vec4(diff + vec3(spec), 1.0);
 }
diff --git a/src/phong.vert b/src/phong.vert
index a0c1fab..3a57004 100755
--- a/src/phong.vert
+++ b/src/phong.vert
@@ -11,6 +11,8 @@ varying vec3 light_ss;
 // ???
 varying vec3 eye_ss;
 
+varying vec2 uv_coord = uv;
+
 /* Position of the light in eye-space.
  */
 const vec3 light_pos_es = vec3(0.0, 3.0, 0.0);