42 lines
1.9 KiB
Markdown
42 lines
1.9 KiB
Markdown
# WebGL2 Pitfalls Reference
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This is a reference document for the [webgl-pitfalls](../techniques/webgl-pitfalls.md) technique.
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## Complete Error Message Reference
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| Error Message | Likely Cause | Solution |
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|---|---|---|
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| `'fragCoord' : undeclared identifier` | Using `fragCoord` instead of `gl_FragCoord.xy` in WebGL2 | Replace with `gl_FragCoord.xy` |
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| `'' : Missing main()` | Fragment shader has no `main()` function | Add `void main() { mainImage(fragColor, gl_FragCoord.xy); }` wrapper |
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| `'functionName' : no matching overloaded function found` | Wrong argument types OR function declared after use | Check types; reorder or forward-declare functions |
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| `'return' : function return is not matching type:` | Return expression type doesn't match declared return type | Verify `vec3 foo()` returns `vec3`, not `float` |
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| `#version` must be first | Leading whitespace when extracting from script tag | Use `.trim()` on shader source string |
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| Uniform returns `null` from `getUniformLocation` | Uniform optimized away for being unused | Ensure uniform is actually referenced in shader code |
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## Type Mismatch Examples
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```glsl
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// ERROR: terrainM expects vec2, passing vec3
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float calcAO(vec3 pos, vec3 nor) {
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float d = terrainM(pos + h * nor); // Wrong: pos + h*nor is vec3
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}
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// FIX: Extract xz components
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float calcAO(vec3 pos, vec3 nor) {
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float d = terrainM(pos.xz + h * nor.xz); // Correct: vec2
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}
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```
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```glsl
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// ERROR: can't access .z on vec2
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vec2 uv = vec2(1.0, 2.0);
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float z = uv.z; // Wrong: vec2 has no .z
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// FIX: use proper swizzle or conversion
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float z = uv.y; // Or if you need third component, use vec3
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```
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## GLSL ES 3.0 Specific Notes
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- All declared `uniform` variables must be used in shader code, otherwise compiler may optimize them away
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- When `gl.getUniformLocation()` returns `null`, setting that uniform triggers `INVALID_OPERATION`
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- Loop counters must be deterministic at runtime — avoid compile-time constant folding issues
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