Astra Engine

Appearance

SkyboxPass ​

SkyboxPass renders a cubemap-based skybox as the scene background. It writes to scene_color after opaque geometry and relies on depth testing to ensure the sky only fills unoccupied pixels.

Render Graph Role ​

AttributeValue
GroupGeometry
Reads-
Writesscene_color
CullableYes

Setup ​

A skybox entity must be present in the scene. The pass resolves its cubemap_id and shader_id each frame through ResourceManager:

cpp
// In Scene::start()
auto* skybox = add_entity<Skybox>("Sky");
skybox->cubemap_id = "sky_cubemap";
skybox->shader_id  = "skybox_shader";
skybox->add_component<MeshComponent>();
skybox->add_component<ResourceComponent>();

If no skybox entity exists, the pass is a no-op for that frame.

Rendering Technique ​

The pass renders a unit cube centered on the camera. The vertex shader strips the translation component from the view matrix so the skybox appears infinitely distant. Depth writes are disabled; the fragment shader outputs to gl_FragDepth = 1.0 so depth testing clips the skybox behind any geometry drawn earlier.

Cubemap Registration ​

Cubemaps are registered as Texture3DDescriptor with six face paths:

cpp
res->register_texture(Texture3DDescriptor::create(
    "sky_cubemap",
    {
        "textures/skybox/right.png"_engine,
        "textures/skybox/left.png"_engine,
        "textures/skybox/top.png"_engine,
        "textures/skybox/bottom.png"_engine,
        "textures/skybox/front.png"_engine,
        "textures/skybox/back.png"_engine,
    }
));

See Textures for cubemap registration details.