Override Shader Chunks

Override shading through chunks

A StandardMaterial's shader is assembled from named chunks (lighting, combine, transform, and more). Overriding one keeps the rest of the pipeline — fog, tonemapping, shadows, skinning, instancing — intact. Reach for a fully custom ShaderMaterial only when the look needs a stage the chunk system does not expose at all (its own vertex/fragment pair and attribute layout); a chunk override is the default for everything else, since it is cheaper and stays integrated.

Pin the version, read the source

Set material.shaderChunksVersion to the installed engine's major.minor (for example '2.22') before shipping any override. Chunk names and their contracts — what a chunk defines, what globals it reads or writes — are version-keyed and change between releases. Read the installed playcanvas source for the exact chunk being touched; do not recall its contract from memory or an older version's documentation.

Clone before overriding a shared material

Clone a material that other mesh instances share — including default and asset-imported materials — before changing its chunks, properties, or material-level parameters for only some meshes, and assign the clone. For per-mesh uniforms, use meshInstance.setParameter() without cloning the material.

Set chunks through the documented accessor

Use material.getShaderChunks(SHADERLANGUAGE_GLSL).set(name, source), and the WGSL equivalent — the public, documented method — not the underlying shaderChunks maps, which are internal. Call material.update() after any change so cached shader variants are cleared.

Emissive-only overrides

An emissivePS override implements void getEmission(), writing the result into dEmission. When the override is meant to fully drive the visible color, zero the material's diffuse/specular and disable useSkybox so no other lighting term still contributes underneath it.

Uniforms are raw

setParameter uploads exactly what it is given, with no color-space conversion. Convert any authored sRGB color with Color#linear() before calling setParameter; an sRGB color passed straight through renders visibly darker and less saturated than it was authored.

Keep vertex chunks instancing-aware

A custom transformCoreVS (or any vertex chunk reading the model matrix) must keep the engine's INSTANCING define path — pulling the per-instance matrix under that define — with a non-instanced fallback that uses matrix_model directly, matching the stock chunk's structure. Dropping this path silently breaks instancing for any mesh instance using the material.

Provide GLSL and WGSL, or pin to WebGL

Override both SHADERLANGUAGE_GLSL and SHADERLANGUAGE_WGSL chunks for anything touched. On a WebGPU device, a chunk supplied only in GLSL forces the material's entire shader — not just that chunk — onto a GLSL-compiled-then-transpiled path; without the optional transpiler modules loaded (the common case), that shader fails to compile. Supply both languages, or explicitly pin the graphics device to WebGL if WGSL support is not required.

Expand bounds for vertex displacement

If the override displaces vertices, expand the mesh's bounds by the maximum displacement (see apply-conventions) — CPU-computed bounds never observe shader-side deformation, so culling breaks silently otherwise.