feat: add forward+ rendering

destrum/assets_src/shaders/skybox.frag

@@ -10,7 +10,6 @@ layout(location = 0) out vec4 outColor;
 layout(push_constant) uniform SkyboxPC {
     mat4 invViewProj;
     vec4 skyboxRot[3];
-    vec3 cameraPos;
     uint skyboxTextureId;
 } pcs;
 
@@ -22,7 +21,8 @@ void main()
     vec4 world = pcs.invViewProj * ndc;
     vec3 worldPos = world.xyz / world.w;
 
-    vec3 dir = normalize(worldPos - pcs.cameraPos);
+    // invViewProj has no translation, so the camera sits at the origin
+    vec3 dir = normalize(worldPos);
     dir.y *= -1.0;
 
     mat3 skyboxRot = mat3(