tone down ambient light a bit

f_shader.glsl

@@ -12,7 +12,7 @@ void main(void)
     float NdotL, RdotEye;
 
     lightDir = normalize(vec3(-0.1, 0, -0.9));
-    color = ambient;  /* ambient light */
+    color = vec4(0.2, 0.2, 0.2, 1.0) * ambient;  /* ambient light */
     n = normalize(normal_i);
 
     NdotL = max(dot(n, -lightDir), 0.0);