Problem Statement

The engine currently has no built-in skybox rendering support. Skyboxes are a standard feature in 3D engines, used to provide a realistic or atmospheric background to scenes. Without this, scenes render against an empty/clear background with no environmental context.

Proposed Solution

Add a skybox rendering system to the engine that:

• Accepts a cubemap texture (loaded via the cubemap loading system — see [FEAT] Add cubemap loading support #567).
• Renders the skybox as a full-screen background cube drawn at maximum depth, behind all scene geometry.
• Integrates cleanly into the existing render pipeline (e.g. as a dedicated render pass or a pre-pass step).
• Exposes a simple API for enabling/disabling the skybox and swapping cubemaps at runtime.

Alternative Solutions

• Render the skybox as a large sphere (skysphere) instead of a cube — simpler geometry but requires equirectangular texture mapping.
• Use a procedural sky shader instead of a cubemap — no asset dependency but higher shader complexity.

Use Cases

• Use case 1: A developer sets a cubemap and sees a seamless sky rendered around the scene without any additional configuration.
• Use case 2: A game switches between indoor and outdoor scenes and swaps the active skybox cubemap at runtime.
• Use case 3: A future PBR pipeline samples the skybox cubemap for image-based lighting (IBL).

Impact

• New rendering feature — additive, no breaking changes to existing render passes.
• Requires the cubemap loading feature ([FEAT] Add cubemap loading support #567) to be completed first.
• Minor GPU cost for the skybox draw call (negligible in practice).

Implementation Details (optional)

• Render a unit cube with depth test set to LESS_OR_EQUAL and the vertex shader outputting pos.xyww to place the cube at maximum depth.
• Use a dedicated skybox vertex and fragment shader that sample the cubemap using the view direction.
• Strip translation from the view matrix so the skybox always appears infinitely distant.
• Integrate as a system or component in the ECS so the skybox can be toggled per-scene.

Additional Context

N/A

Related Issues

• [FEAT] Add cubemap loading support #567 (cubemap loading — this issue depends on it)