fix light calc with backlight

assets/shader/standard.frag

@@ -75,9 +75,9 @@ vec3 blinnphong(vec3 N, vec3 V, vec3 L, vec3 color){
     float spec_coeff = pow(max(dot(H, N), 0.0), shininess);
     if (diff_coeff <= 0.0 || isnan(spec_coeff))
         spec_coeff = 0.0;
+
     // final lighting model
     return vec3(
-        ambient * color +
         diffuse * diff_coeff * color +
         specular * spec_coeff
     );

src/GLVisualize/visualize/surface.jl

@@ -64,8 +64,8 @@ function light_calc(x::Bool)
         vec3 L      = normalize(o_lightdir);
         vec3 N      = normalize(o_normal);
         vec3 light1 = blinnphong(N, o_camdir, L, color.rgb);
-        color       = vec4(light1, color.a) + 
-            backlight * vec4(blinnphong(N, o_camdir, -L, color.rgb), color.a);
+        vec3 light2 = blinnphong(N, o_camdir, -L, color.rgb);
+        color       = vec4(ambient * color.rgb + light1 + backlight * light2, color.a);
         """
     else
         ""