HDRI sky sources

All three original 2048 × 1024 RGBE HDR panoramas are from Poly Haven. They are licensed CC0 1.0, which permits commercial use and redistribution. Cost: €0. No account, purchase, or attribution requirement. Credits are retained here voluntarily.

SKY-ASSETS.json records official API URLs, exact download URLs, provider MD5 checksums, verified SHA-256 hashes, file sizes, and license links. Tools/fetch_skies.py reproduces the download through the official API and fails on checksum mismatches. The delivered HDR files are unmodified.

Import and lighting integration

Editor/SkyImportSettings.cs automatically imports only HDRs in Resources/Skies as linear cubemaps, with trilinear mipmaps and Standalone BC6H compression. A 512-pixel cubemap face preserves the angular information of the 2048-pixel panorama. Runtime loading uses Resources.Load<Cubemap>(resourceKey). Rampage.Editor.SkyImportSettings.ReimportSkies() is available for the configurator or menu.

In HDRP 17.3, add HDRISky to the profile, assign hdriSky, and set VisualEnvironment.skyType to (int)SkyType.HDRI. Use skyIntensityMode = SkyIntensityMode.Lux, upperHemisphereLuxValue to the measured source integral, and desiredLuxValue to the artistic target. Runtime-created profiles must set the source integral explicitly; the editor's automatic measurement is not involved.

These targets are the current runtime art settings, not a claim of rendered calibration. Fixed camera exposure remains EV13 for forest/desert and EV9.5 for the readable blue-hour city. Source integrals were computed from original linear RGBE values using Rec.709 luminance and ∫upper L cos(theta) dOmega; see QA/SkyMeasurements.json. Lux mode applies exactly target / source. Exposure mode instead uses log2(target / source * ColorUtils.lensImperfectionExposureScale) because HDRP's exposure conversion includes the lens attenuation scale.

Sky rotation only rotates azimuth. Align the sky's bright region with the directional light after import; do not infer Unity cubemap azimuth from the source panorama without checking its mapping. The forest source sun is approximately 37.9° above the horizon, the desert bright region approximately 9.9°. The replacement changes source maps and their lux normalization only; existing key-light direction and color remain art settings pending the next actual render review. QA/SkyPreviews.png shows the full upper hemisphere of each delivered HDR, using a simple source-only Reinhard preview. It does not replace the HDR assets or demonstrate final game lighting.

Cloud-detail correction, 2026-09-14

The earlier Kloofendal 28d Misty source is nearly uniform grey mist, and Qwantani Dusk 2 has a smooth lavender upper sky with clouds confined to the horizon. Decoding the original HDRs reproduced the flat backgrounds seen in the game; HDRI loading and linear BC6H import were not the cause. The replacement forest source contains distinct photographic white cloud structure. Belfast Sunset retains a violet-blue dusk palette with visible clouds across a much larger part of the sky. Both were visually checked from the actual 2K RGBE files before selection. The delivered files remain unmodified originals and preserve the existing Unity resource paths and GUIDs.

Analytic fog is unchanged in this asset correction. In local HDRP 17.3 source, Fog.maxFogDistance defaults to 5000m and applies that distance to sky pixels. With the current forest base -15m, maximum 140m, mean free path 1000m and a camera at 20m, the analytic formula gives approximately 65% opacity at the exact horizon, 5.3% at 5° elevation, and 1.4% at 20°. A 500m cap would clear the horizon substantially but would barely affect the upper sky; it cannot supply cloud structure absent from an asset. A separate horizon change needs an actual comparison capture.

Alpine clear-day source, 2026-09-15

Skies/AlpineDay adds the original 2K Kloofendal 43d Clear (Pure Sky) by Greg Zaal, CC0. The actual RGBE source was decoded and visually inspected: blue upper sky, sparse white cloud structure, a visible sun and no photographic terrain. It is not an overcast source. The delivered HDR bytes are unchanged; no pixel tint, gamma recoloring, or artificial HDR amplification was applied. Runtime exposure, fog and sun alignment still require a real gameplay view.

Its measured upper-hemisphere luminance integral is 5.457733041849752, and its brightest source elevation is 42.978515625 degrees. In HDRP lux mode assign this integral to upperHemisphereLuxValue; keep the intended lighting target separate in desiredLuxValue. Brightest source longitude is 216.123046875 degrees, which is a panorama coordinate, not a verified Unity yaw. Import settings match the existing linear cubemaps: 512px Standalone BC6H faces, trilinear mipmaps, no CPU-readable copy.

Full API metadata, publisher size/MD5 checks and SHA-256 are recorded in ALPINE-ROAD-ASSETS.json. Tools/Art/prepare_alpine_road_assets.py --publish reproduces both this sky and the gray Clean Asphalt material set. The source-only Reinhard preview is ArtSource/AlpineRoadAssets/kloofendal_43d_clear_puresky_2k-upper-preview.png; it is not a gameplay screenshot.