feat: add ambient component to fragment shader for Phong shading start

shaders/simple.frag

@@ -6,7 +6,13 @@ in vec3 vNormal;
 
 void main() {
     vec3 lightDirection = normalize(vec3(0.8, -0.5, 0.6));
+    // ambient component
+    float ambientStrength = 0.1;
+    vec3 ambient = ambientStrength * vColor.rgb;
+    // diffuse component (Lambert)
     float lambert = max(0.0, dot(normalize(vNormal), -lightDirection));
-    vec3 litColor = vColor.rgb * lambert;
-    color = vec4(litColor, vColor.a);
+    vec3 diffuse = vColor.rgb * lambert;
+    // combine ambient and diffuse
+    vec3 result = ambient + diffuse;
+    color = vec4(result, vColor.a);
 }