Implement lambertian shading w/ directional light

vert.glsl

@@ -13,5 +13,5 @@ layout(push_constant) uniform MVP {
 
 void main() {
 	gl_Position = mvp.proj * mvp.view * mvp.model * vec4(position, 1.0);
-	frag_normal = normal;
+	frag_normal = mat3(mvp.model) * normal;
 }