A GPU-accelerated procedural skybox engine for low-earth orbit simulation. Generate photorealistic space backgrounds — complete with the Milky Way, 100K+ catalog stars, 88 IAU constellations, volumetric nebulae, sun with god rays and lens flare — then export as cubemap PNGs or HDR for Unity and other game engines.
Built for Geocore — a 3D modern educational geography game, using a camera perspective from low-earth orbit.
Pro players on Geocore for Windows can import their own sky from a cross-layout PNG.
- Open skybox.geocore.fun and design your sky. The Orbit presets (Orbit Clean, Quiet Orbit, Galactic Core, Orbital Sunrise and the rest from preset 7 on) are tuned as backdrops for the globe.
- Press Export for Geocore in the Export panel. It sets Format to Cross Layout PNG and Resolution to 1024 × 1024 and exports
skybox_cross_1024.png, a 4096 × 3072 image, then tells you the file size. (Doing it by hand works the same: those two settings, then Export Skybox.) The resolution is per face, and the game accepts square power-of-two faces of 1024 px or less, so 2048 and up are refused. - In Geocore for Windows (signed in, Geocore Pro), open Settings, find Custom skybox, paste the full path to the PNG (Shift+right-click ▸ Copy as path works), and press Import skybox. Reset skybox restores the default sky.
The game also limits the file to 16 MiB. A busy sky with nebulae and many stars compresses poorly, so if 1024 is refused as too large, export at 512 instead (the engine warns you when an export is over the limit). Every built-in preset comes in well under it at 1024. The import lasts until Geocore closes and is not saved. The full steps and refusal messages are in the Geocore FAQ; the same steps are in the app under Use in Geocore in the toolbar.
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| Feature | Description |
|---|---|
| Milky Way | Physically-based galactic plane with customizable tilt, core brightness, and arm structure |
| Catalog Stars | 119,614 real stars from the HYG v4.2 database with accurate B-V color mapping and magnitude-based sizing |
| Procedural Stars | 100K+ seeded point sprites with adjustable count, brightness, size, and color variation |
| Nebula | Volumetric 4D simplex noise FBM with 3-color gradient, tunable density, falloff, and octaves |
| Sun | Directional light with disk, corona, limb darkening, and atmospheric glow |
| Constellations | All 88 IAU constellation lines, labels, and boundary polygons |
| Named Star Labels | Labels for prominent named stars (Sirius, Betelgeuse, Polaris, etc.) |
| Background | Solid color fill layer |
| Feature | Description |
|---|---|
| God Rays | Volumetric light scattering with radial blur + cross-face analytical glow |
| Bloom | Multi-pass Gaussian bloom with configurable threshold, soft knee, and iterations |
| Lens Flare | Analytical ghost elements, halo ring, anamorphic streaks, and chromatic aberration |
| Feature | Description |
|---|---|
| Individual Face PNGs (ZIP) | 6 cubemap faces at up to 8K resolution |
| Cross Layout PNG | Single 4:3 composite image |
| HDR (Radiance RGBE) | High dynamic range cubemap export |
| Tiled Rendering | GPU-friendly tile-based rendering for 8K/16K+ exports without VRAM limits |
| Batch Export | Export all presets in one operation |
| Feature | Description |
|---|---|
| Preset System | 16 built-in presets (10 tuned as Geocore orbit backdrops) + save/load/import/export custom presets (JSON) |
| Undo/Redo | Full parameter history with keyboard shortcuts (Ctrl+Z / Ctrl+Shift+Z) |
| A/B Comparison | Side-by-side before/after comparison with split slider |
| Session Persistence | Auto-saves all parameters to localStorage; restores on reload |
| Real-time Histogram | Live RGB histogram with async GPU readback (no stalls) |
| Performance Monitor | FPS/frame time/render time overlay |
| Feature | Description |
|---|---|
| WebGL2 + GLSL 300 es | Hardware-accelerated rendering pipeline |
| 10-layer compositing | Sorted render layers with per-layer enable/disable |
| Cubemap FBO | Renders all 6 faces with shared framebuffer |
| Async Readback | PBO-based pixel readback with fence sync for stall-free histogram |