Section: Illuminating the Text with a Light

text_and_shaders.ini

@@ -28,7 +28,7 @@ String = HELLO WORLD!!
 Font = plump
 
 [TextShader]
-ParamList = texture # BorderColor ; We've added a new parameter
+ParamList = texture # BorderColor # LightPos # LightColor; We've added a new parameter
 Code = "
 void main() {
     // Get the texture value for the current pixel
@@ -37,9 +37,24 @@ void main() {
     // Here's the fun; We blend in the border color based on R channel
     gl_FragColor.rgb = mix(vec3(1.0), BorderColor, tex.r) * gl_Color.rgb;
 
+    // Let's derive the surface normal from the green and blue channels
+    vec3 normal = normalize(vec3(tex.g-0.5, tex.b-0.5, 0.5));
+
+    // Let's find the unit vector pointing from this pixel towards the light
+    vec3 light_dir = normalize(LightPos-gl_FragCoord.xyz);
+
+    // The illumination of a Lambertian surface is the dot product
+    // of the surface normal and the unit vector towards the light
+    float illumination = max(0.0, dot(normal, light_dir));
+
+    // Let's apply the light color and the illumination
+    gl_FragColor.rgb *= LightColor * illumination;
+
     // Set the pixel alpha to the texture's alpha multiplied by the object's
     gl_FragColor.a = tex.a * gl_Color.a;
 }"
 BorderColor = (0,0,255) ; Let's make the border blue, just for fun.
+LightPos = (200,150,100) ;
+LightColor = (1,0.7,0.7) ;
 
 @plump.ini@