Three.js Shader Compilation Error: geometryNormal Undeclared

Based on the error you're encountering with the PhysicalMaterial shader in Three.js r137, it appears that the geometryNormal variable is being used without being properly declared in the shader code.

Understanding the Issue

The error occurs because the shader is trying to use geometryNormal in the following line:

GLSLCopied
vec3 dxy = max( abs( dFdx( geometryNormal ) ), abs( dFdy( geometryNormal ) ) );

But the variable geometryNormal hasn't been defined earlier in the shader code, leading to the compilation error.

Potential Solutions

1. Use the correct normal variable: In Three.js materials, the normal vector is typically available as either normal, vNormal, or geometry.normal depending on the shader context. You should replace geometryNormal with the appropriate normal variable that is defined in your shader.

2. Add a declaration for geometryNormal: If you're customizing the shader, you might need to add a declaration for geometryNormal before it's used, possibly by computing it from other available geometry data.

3. Check for version compatibility: This could be a bug specific to r137. Consider checking if this issue is fixed in newer versions of Three.js or if there's a known workaround.

4. Inspect the full shader code: The complete shader code might provide more context about what normal variable should be used instead.

If you're using a custom ShaderMaterial or modifying the built-in materials, you'll need to ensure that all variables are properly declared before use. The GLSL version (GLSL1 or GLSL3) might also affect how variables need to be declared.

For a more specific solution, you might need to examine the complete shader code or check the Three.js GitHub repository for any reported issues related to this problem in r137.