CesiumJS Custom Shader

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name: cesiumjs-custom-shader
description: "CustomShader authoring — vertexShaderText and fragmentShaderText against VertexInput, FragmentInput, FeatureIds, Metadata, czm_modelMaterial. Use when reading EXT_mesh_features or EXT_structural_metadata property textures/tables, vertex displacement, or shading VoxelPrimitive."
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# CesiumJS CustomShader

Version baseline: CesiumJS 1.142. All imports use ES module style.

`CustomShader` injects user GLSL into the `Model` / `Cesium3DTileset` / `VoxelPrimitive` rendering pipeline. It exposes glTF attributes, feature IDs, and `EXT_structural_metadata` to per-vertex and per-fragment code, and returns values through the built-in `czm_modelVertexOutput` and `czm_modelMaterial` structs.

Use this skill for **writing the shader body**. Use:
- `cesiumjs-materials-shaders` — for Fabric `Material`, `ImageBasedLighting`, `PostProcessStage` (bloom, SSAO, FXAA, tonemapping).
- `cesiumjs-3d-tiles` — for declarative per-feature coloring via `Cesium3DTileStyle`, and for `VoxelPrimitive` setup/configuration.
- `cesiumjs-models-particles` — for `Model.fromGltfAsync`, animations, `ModelFeature.getProperty()`.

## Out of scope

- **Fabric `Material`** for entity polylines/polygons/walls — see `cesiumjs-materials-shaders`.
- **`PostProcessStage`** screen-space effects — see `cesiumjs-materials-shaders`.
- **`ImageBasedLighting`** — see `cesiumjs-materials-shaders`.
- **`Cesium3DTileStyle`** declarative JSON styling — see `cesiumjs-3d-tiles`. **Do not combine with CustomShader on the same tileset.**
- **Authoring `EXT_structural_metadata` / `EXT_mesh_features` in glTF** — tooling concern, not runtime.

## Minimal example