feat: Snow Cover

[ThePagi]

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A feature handling seasonal snow cover, also usable for ash and similar materials that cover large areas. The feature blends a snow texture into the original rendered textures based on the configured criteria. The snow textures are always projected from the top (with parallax shifting the uv to avoid lines on vertical surfaces) and foliage optionally has snow only around the edges.

• A json config is used to control snow cover for each worldspace or cell.
• A main and optionally an alternative set of textures (by default marsh ice) define the look of the snow.
• There are additional material properties and tints for the textures.
• Surface angles at which the main and alternative textures appear are configurable.
• Snow cover is controlled based on altitude and weather.
• Snowy weather creates temporary snow, rain dissolves it.
• The altitude the snow appears at (no matter the weather) can be configured to change based on game months.
• Rain temporarily changes 'permanent' snow to the alternative set of textures.
• An optional grayscale texture can be used to offset the altitude snow appears at. By default a texture mimicking vanilla snow placement is used.
• Optionally the hue of foliage is shifted towards brown based on the altitude.

Summary by CodeRabbit

• New Features

  • Realistic Snow Cover: dynamic accumulation/melting, seasonal timing, slope-based coverage, foliage tinting, PBR and VR-aware behavior, in-app UI with per-world presets (Tamriel, Whiterun, Markarth, Riften, Solitude, Windhelm) and per-world toggles.

• Documentation

  • Added per-world configuration presets, whitelist/blacklist entries, and UI controls for tuning snow, textures, and foliage.

• Chores

  • Integrated Snow Cover into rendering/features pipeline, resource loading/reload, persistent config, and improved ID-list parsing for whitelist/blacklist.