Add basic lighting

shaders/lighting.glsl

@@ -0,0 +1,16 @@
+uniform sampler2D texture;
+uniform float ambient;
+uniform bool has_texture;
+
+void main()
+{
+    // lookup the pixel in the texture
+    vec4 pixel = texture2D(texture, gl_TexCoord[0].xy);
+
+    // multiply it by the color
+    vec4 col = gl_Color;
+    if (has_texture) {
+        col = gl_Color * pixel;
+    }
+    gl_FragColor = vec4(col.x * ambient, col.y * ambient, col.z * ambient, col.w);
+}