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Copy assigned by-value parameters when inlining shader functions - #19077
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🟡 Changes recommended
The inliner misses writes and writable calls that can mutate callers’ by-value arguments, and copied locals lose precision qualifiers that can affect shader results.
3 open issues
What changed in this PR
This PR updates ShaderCodeInliner to protect caller variables when inlined shader functions assign to by-value parameters, addressing an OpenPBR anisotropy rendering issue in Babylon Native and the WebGPU GLSL path.
Changes:
- Detects assigned by-value parameters and creates local copies at each call site.
- Preserves direct substitution for read-only parameters.
- Adds unit tests for caller-variable protection and read-only substitution.
| File | Description |
|---|---|
packages/dev/core/test/unit/Engines/shaderCodeInliner.test.ts |
Adds regression tests for assigned and read-only parameters. |
packages/dev/core/src/Engines/Processors/shaderCodeInliner.ts |
Detects parameter writes and generates local argument copies during inlining. |
Review effort: Balanced
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deltakosh
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Hello @bkaradzic-microsoft,
The fix is correct and scoped: directly written by-value parameters get local copies, read-only substitution stays unchanged, and the tests cover both.
An optional, non-blocking follow-up is handling indirect writes through out/inout calls, which still leak to the caller as before.
Thanks!
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Snapshot stored with reference name: Test environment: To test a playground add it to the URL, for example: https://snapshots-cvgtc2eugrd3cgfd.z01.azurefd.net/refs/pull/19077/merge/index.html#WGZLGJ#4600 Links to test your changes to core in the published versions of the Babylon tools (does not contain changes you made to the tools themselves): https://playground.babylonjs.com/?snapshot=refs/pull/19077/merge To test the snapshot in the playground with a playground ID add it after the snapshot query string: https://playground.babylonjs.com/?snapshot=refs/pull/19077/merge#BCU1XR#0 If you made changes to the sandbox or playground in this PR, additional comments will be generated soon containing links to the dev versions of those tools. |
🟢 Memory Leak Test Results4 passed, 0 leaked out of 4 scenarios 🟢 All memory leak tests passed — no leaks detected. Passed Scenarios (4)
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⚡ Performance Test Results🟢 All performance tests passed — no regressions detected. |
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WebGL2 visualization test reporter: |
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Visualization tests for WebGPU |
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deltakosh
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Hello @bkaradzic-microsoft,
Please restrict OpaqueTypeRegexp (shaderCodeInliner.ts:15) to complete opaque type names. It is not anchored at the end, so it matches valid structs such as textureState or samplerParams; assigning to their by-value parameters now modifies the caller instead of a local copy. Please add regression coverage for this case.
Thanks!
ShaderCodeInliner substitutes the call arguments for the parameter names in the function body. When the body assigns to a by-value parameter, the assignment is applied to the caller's variable. For example, sampleRadianceAnisotropic does `alphaG = alphaB;`, which became `specularAlphaG = alphaB;` in the caller and changed the OpenPBR anisotropic environment specular/diffuse mix on Babylon Native and WebGPU. Such parameters are now copied into a local variable at each call site. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Copilot-Session: 60c2ec68-6de1-445d-9fc9-b699db737eae
- Detect writes via assignment, ++/--, nested subscripts/swizzles, and passing as out/inout argument (user functions and GLSL builtins) - Strip comments before analysis - Preserve precision qualifiers on copies; never copy opaque types - Collision-free names for copies and return temporaries Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Copilot-Session: 60c2ec68-6de1-445d-9fc9-b699db737eae
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Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Copilot-Session: 60c2ec68-6de1-445d-9fc9-b699db737eae
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Fixed in 27e1b64. |
deltakosh
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Hello @bkaradzic-microsoft,
The anchored opaque-type matching and the struct regression test resolve my earlier request.
Thanks!
🟢 Memory Leak Test Results4 passed, 0 leaked out of 4 scenarios 🟢 All memory leak tests passed — no leaks detected. Passed Scenarios (4)
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WebGL2 visualization test reporter: |
⚡ Performance Test Results🟢 All performance tests passed — no regressions detected. |
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Visualization tests for WebGPU |
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Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Copilot-Session: 60c2ec68-6de1-445d-9fc9-b699db737eae
_replaceNames now skips identifiers preceded by a "." (allowing whitespace and comments in between), so a copied parameter named like a swizzle or struct field (e.g. "x" in "v.x") no longer rewrites the member access. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Copilot-Session: 60c2ec68-6de1-445d-9fc9-b699db737eae
deltakosh
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Hello @bkaradzic-microsoft,
Thanks for the quick fix. IsMemberName now keeps member and swizzle names (v.x, v . /* c */ x, s.a) intact while standalone references still use the copy, which resolves the swizzle regression. The regression test covers the whitespace and comment forms.
Non-blocking edge case for a follow-up: the line-comment check at shaderCodeInliner.ts:61-64 looks for the first // on the line, so a // inside a closed block comment earlier on the same line (for example x = 2.0; /* see http://... */ return v.x; with a copied x) is taken as a line comment, and the swizzle is still rewritten. It needs a fairly contrived combination, so I am not blocking on it.
LGTM, thanks!
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Copilot-Session: 60c2ec68-6de1-445d-9fc9-b699db737eae
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…eters _replaceNames now skips struct bodies, which only contain type and field names. Previously a local struct field named like a parameter was renamed while its member accesses were preserved, producing invalid GLSL. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Copilot-Session: 60c2ec68-6de1-445d-9fc9-b699db737eae
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Hello @bkaradzic-microsoft,
The struct-field exclusion is the right idea, but FindStructBodies (shaderCodeInliner.ts:78-86) runs its regex on the raw code, comments included. A function body containing a commented-out // struct S { makes ExtractBetweenMarkers start at that { (it starts mid-comment, so it does not know it is inside one) and close on the function's own }. Everything after the comment is then treated as a struct body, so parameter (and return) substitution is skipped there and the inlined shader no longer compiles.
Please mask comments with spaces (same length, so offsets stay valid) before scanning for struct bodies, and add a regression test with a commented-out struct S { followed by a use of the parameter.
Thanks!
A commented-out "struct S {" no longer starts a struct body, and comments in a
struct header ("struct S /* c */ {") are treated as whitespace.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 60c2ec68-6de1-445d-9fc9-b699db737eae
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@deltakosh Fixed in 44aabb1. Added the regression "ignores struct declarations inside comments": a function with both comment forms followed by |
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Hello @bkaradzic-microsoft,
MaskComments blanks line and block comments while keeping offsets, and FindStructBodies now scans the masked code, so a commented-out struct S { no longer swallows the function body. The regression tests cover it. Approved.
Thanks!
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Please make sure to label your PR with "bug", "new feature" or "breaking change" label(s). |
The UMD bundles must stay ES6 (test:escheck), and lookbehind is ES2018. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Copilot-Session: 60c2ec68-6de1-445d-9fc9-b699db737eae
deltakosh
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Hello @bkaradzic-microsoft,
The \b replacements keep the same matches without the lookbehinds, which is safer for older targets. Still approved.
Thanks!
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Please make sure to label your PR with "bug", "new feature" or "breaking change" label(s). |
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Reviewer - this PR has made changes to one or more package.json files. |
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Snapshot stored with reference name: Test environment: To test a playground add it to the URL, for example: https://snapshots-cvgtc2eugrd3cgfd.z01.azurefd.net/refs/pull/19077/merge/index.html#WGZLGJ#4600 Links to test your changes to core in the published versions of the Babylon tools (does not contain changes you made to the tools themselves): https://playground.babylonjs.com/?snapshot=refs/pull/19077/merge To test the snapshot in the playground with a playground ID add it after the snapshot query string: https://playground.babylonjs.com/?snapshot=refs/pull/19077/merge#BCU1XR#0 If you made changes to the sandbox or playground in this PR, additional comments will be generated soon containing links to the dev versions of those tools. |
🟢 Memory Leak Test Results4 passed, 0 leaked out of 4 scenarios 🟢 All memory leak tests passed — no leaks detected. Passed Scenarios (4)
|
⚡ Performance Test Results🟢 All performance tests passed — no regressions detected. |
|
WebGL2 visualization test reporter: |
|
Visualization tests for WebGPU |
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Copilot-Session: 60c2ec68-6de1-445d-9fc9-b699db737eae
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ShaderCodeInliner(used byNativeEngine) inlines a function by substituting the call arguments for the parameter names in the function body. If the body assigns to a by-value parameter, the assignment is applied to the caller's variable.sampleRadianceAnisotropicinopenpbrIblFunctions.fxdoesalphaG = alphaB;. After inlining, this becamespecularAlphaG = alphaB;inopenpbrEnvironmentLighting.fx. That zeroedspecularAlphaGat full anisotropy and changed the environment specular/diffuse mix that follows. WebGL doesn't inline, so it was unaffected. When the body writes to a by-value parameter (notout/inout/const, not an array), the inliner now copies the argument into a local variable at each call site. Parameters that are only read are still substituted directly, so the generated code is unchanged for every other function. Results: - OpenPBR IBL Anisotropy Metal (#GRQHVV#208) on Babylon Native D3D11: the diff against the reference drops from 3.47% to 0.50%. - No regressions across the rest of the Babylon Native validation suite (698/698). - Added a unit test for the inliner.