[Impeller] include uniform info in impellerc json reflections #179317

flar · 2025-12-02T02:00:42Z

Impellerc json reflection files include most of the data about the shader, but they did not include the information about non-sampler uniforms until now. This new information will be useful for tools that extract information on uniform locations from shaders.

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I read the Contributor Guide and followed the process outlined there for submitting PRs.
I read the Tree Hygiene wiki page, which explains my responsibilities.
I read and followed the Flutter Style Guide, including Features we expect every widget to implement.
I signed the CLA.
I listed at least one issue that this PR fixes in the description above.
I updated/added relevant documentation (doc comments with ///).
I added new tests to check the change I am making, or this PR is test-exempt.
I followed the breaking change policy and added Data Driven Fixes where supported.
All existing and new tests are passing.

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Note: The Flutter team is currently trialing the use of Gemini Code Assist for GitHub. Comments from the gemini-code-assist bot should not be taken as authoritative feedback from the Flutter team. If you find its comments useful you can update your code accordingly, but if you are unsure or disagree with the feedback, please feel free to wait for a Flutter team member's review for guidance on which automated comments should be addressed.

engine/src/flutter/impeller/compiler/compiler_test.h

engine/src/flutter/impeller/compiler/compiler_unittests.cc

engine/src/flutter/impeller/fixtures/sample_with_uniforms.frag

flar · 2025-12-04T00:40:21Z

engine/src/flutter/impeller/fixtures/sample_with_uniforms.frag

+out vec4 frag_color;
+
+void main() {
+  frag_color = frag_color;


World's most useful fragment shader? You be the judge... ;)

…-json-output

flar · 2025-12-04T06:13:13Z

/gemini review

gemini-code-assist

Code Review

This pull request adds support for reflecting non-sampler uniforms in impellerc's JSON output. This is achieved by adding a new section to reflector.cc to process gl_plain_uniforms. The changes include refactoring the compiler tests to better separate test suites for different targets and adding new tests to verify the uniform reflection. New shader fixtures are also added for these tests. The changes look good and achieve the goal. I have a few suggestions to improve correctness in the test fixtures, and performance and maintainability in the implementation.

engine/src/flutter/impeller/compiler/compiler_unittests.cc

gemini-code-assist · 2025-12-04T06:15:15Z

engine/src/flutter/impeller/compiler/reflector.cc

+      for (auto uniform : uniforms_json.value()) {
+        uniform["descriptor_type"] = "DescriptorType::kUniform";
+        uniforms.emplace_back(std::move(uniform));
+      }


The current loop creates a copy of each uniform object from uniforms_json. To improve performance by avoiding unnecessary copies, you can use a range-based for loop with an rvalue reference (&&) and std::move to iterate over and move the elements from uniforms_json.value() into the uniforms array.

Suggested change

for (auto uniform : uniforms_json.value()) {

uniform["descriptor_type"] = "DescriptorType::kUniform";

uniforms.emplace_back(std::move(uniform));

}

for (auto&& uniform : std::move(uniforms_json.value())) {

uniform["descriptor_type"] = "DescriptorType::kUniform";

uniforms.emplace_back(std::move(uniform));

}

This should probably be copied into a new issue and applied throughout the reflector.cc file...

See #179434

engine/src/flutter/impeller/fixtures/sample_with_positioned_uniforms.frag

engine/src/flutter/impeller/fixtures/sample_with_uniforms.frag

flar · 2025-12-04T06:15:38Z

engine/src/flutter/impeller/compiler/compiler_unittests.cc

+        UniformInfo::Vec3("uVec3", 3u),
+        UniformInfo::Vec4("uVec4", 2u),
+        UniformInfo::Mat4("uMat4", 1u),
+        UniformInfo::Float("uFloatNotPositioned2", 2u),


The compiler and JSON reflection generated duplicate locations here at 2u. This is likely the code not expecting us to mix positioned and unpositioned uniforms?

flar · 2025-12-04T06:16:53Z

engine/src/flutter/impeller/compiler/compiler_unittests.cc

+        UniformInfo::Vec2("uVec2", 3u),
+        UniformInfo::Vec3("uVec3", 4u),
+        UniformInfo::Vec4("uVec4", 5u),
+        UniformInfo::Mat4("uMat4", 6u),


Note that the locations are not reused between samplers and float uniforms even though they are in essentially different "uniform location" spaces.

chinmaygarde · 2025-12-04T22:12:43Z

engine/src/flutter/impeller/compiler/reflector.cc

+  {
+    auto& uniforms = root["uniforms"] = nlohmann::json::array_t{};
+    if (auto uniforms_json =
+            ReflectResources(shader_resources.gl_plain_uniforms);


Dang. Such and odd thing to call these uniforms. Good catch.

…ns (flutter/flutter#179317)

Roll Flutter from 69d8710fadcd to 5b8720312a94 (42 revisions) flutter/flutter@69d8710...5b87203 2025-12-05 [email protected] Roll Packages from d39e481 to b17d3ff (3 revisions) (flutter/flutter#179505) 2025-12-05 [email protected] Move target_cpu into use_rbe block in Fuchsia build (flutter/flutter#179458) 2025-12-05 [email protected] Roll Skia from fe6bf18a3f6b to a31411879251 (3 revisions) (flutter/flutter#179499) 2025-12-05 [email protected] Force WASM single threading in Chrome extensions. (flutter/flutter#179400) 2025-12-05 [email protected] Roll Skia from aea282ea0bcd to fe6bf18a3f6b (7 revisions) (flutter/flutter#179489) 2025-12-05 [email protected] fix: check both pointer count and action before reusing MotionEvent (flutter/flutter#178528) 2025-12-05 [email protected] Roll Fuchsia Linux SDK from VtDPX2k1kosHxjKUE... to vDeTl_KBeLJY8nCAx... (flutter/flutter#179478) 2025-12-05 [email protected] [ Widget Preview ] Add embedded Widget Inspector support (flutter/flutter#178116) 2025-12-05 [email protected] bubble up fragment shader errors (flutter/flutter#179363) 2025-12-05 [email protected] Roll Dart SDK from eda82318e193 to 42fe3327abca (1 revision) (flutter/flutter#179472) 2025-12-05 [email protected] [Android 16] Use AVD With New Android Renderer (flutter/flutter#179306) 2025-12-05 [email protected] Unpin `package:dwds` dependency (flutter/flutter#179462) 2025-12-05 [email protected] [Impeller] include uniform info in impellerc json reflections (flutter/flutter#179317) 2025-12-05 [email protected] Roll Skia from 1591b066f49b to aea282ea0bcd (1 revision) (flutter/flutter#179468) 2025-12-04 [email protected] Roll Skia from e1923478562b to 1591b066f49b (3 revisions) (flutter/flutter#179460) 2025-12-04 [email protected] Cherry-pick flutter 3.38.4 changelog back to master. (flutter/flutter#179463) 2025-12-04 [email protected] [web] Add clone method to LayerPicture and dispose pictures in PictureLayer (flutter/flutter#179162) 2025-12-04 [email protected] Fixes merge conflict from high bitrate texture tests (flutter/flutter#179416) 2025-12-04 [email protected] Fix typos in `VirtualDisplayController.java` (flutter/flutter#179411) 2025-12-04 [email protected] Roll Dart SDK from 2de44cc08970 to eda82318e193 (1 revision) (flutter/flutter#179453) 2025-12-04 [email protected] Roll Skia from 55d94a54f453 to e1923478562b (1 revision) (flutter/flutter#179449) 2025-12-04 [email protected] Roll Packages from 8cb4903 to d39e481 (8 revisions) (flutter/flutter#179451) 2025-12-04 [email protected] Add DropdownMenu.selectOnly (flutter/flutter#179189) 2025-12-04 [email protected] Roll Dart SDK from 7e6bfc6af55c to 2de44cc08970 (6 revisions) (flutter/flutter#179443) 2025-12-04 [email protected] Roll Skia from b8f79d7316c0 to 55d94a54f453 (1 revision) (flutter/flutter#179439) 2025-12-04 [email protected] Revise README for link updates and terminology changes (flutter/flutter#179357) 2025-12-04 [email protected] Roll Skia from ce19122e3982 to b8f79d7316c0 (3 revisions) (flutter/flutter#179436) 2025-12-04 [email protected] Update some BottomNavigationBar comments to reflect theme normalization (flutter/flutter#179404) 2025-12-04 [email protected] Replace use of eglCreateImage with eglCreateImageKHR to reduce EGL requirement (flutter/flutter#179310) 2025-12-04 [email protected] Roll Skia from 81a9a0751f00 to ce19122e3982 (5 revisions) (flutter/flutter#179430) 2025-12-04 [email protected] [impellerc] adds entry prefix flag to avoid shader collisions (flutter/flutter#179160) 2025-12-04 [email protected] [Windows] Allow apps to prefer high power GPUs (flutter/flutter#177653) 2025-12-04 [email protected] [ Infra ] Shard `Windows tool_tests_commands` (flutter/flutter#179409) 2025-12-04 [email protected] [flutter_tools] Fix filename typo (flutter/flutter#179427) 2025-12-04 [email protected] Marks Linux_pixel_7pro draw_arcs_all_stroke_styles_perf__timeline_summary to be unflaky (flutter/flutter#179392) 2025-12-03 [email protected] Marks Mac_ios draw_arcs_all_fill_styles_perf_ios__timeline_summary to be unflaky (flutter/flutter#179391) 2025-12-03 [email protected] Marks Linux_pixel_7pro draw_arcs_all_fill_styles_perf__timeline_summary to be unflaky (flutter/flutter#179390) 2025-12-03 [email protected] Roll Abseil to 564023aa5376 (flutter/flutter#179421) 2025-12-03 [email protected] Made wide gamut tests give more information in their failure (flutter/flutter#179415) 2025-12-03 [email protected] Roll Skia from c20f797ab6f9 to 81a9a0751f00 (5 revisions) (flutter/flutter#179417) 2025-12-03 [email protected] Migrate samples and docs to RadioGroup (flutter/flutter#179158) 2025-12-03 [email protected] Roll Dart SDK to 3.11.0-200.1.beta (flutter/flutter#179399) If this roll has caused a breakage, revert this CL and stop the roller using the controls here: https://autoroll.skia.org/r/flutter-packages ...

…r#179317)  Impellerc json reflection files include most of the data about the shader, but they did not include the information about non-sampler uniforms until now. This new information will be useful for tools that extract information on uniform locations from shaders. ## Pre-launch Checklist - [x] I read the [Contributor Guide] and followed the process outlined there for submitting PRs. - [x] I read the [Tree Hygiene] wiki page, which explains my responsibilities. - [x] I read and followed the [Flutter Style Guide], including [Features we expect every widget to implement]. - [x] I signed the [CLA]. - [x] I listed at least one issue that this PR fixes in the description above. - [x] I updated/added relevant documentation (doc comments with `///`). - [x] I added new tests to check the change I am making, or this PR is [test-exempt]. - [x] I followed the [breaking change policy] and added [Data Driven Fixes] where supported. - [x] All existing and new tests are passing. If you need help, consider asking for advice on the #hackers-new channel on [Discord]. **Note**: The Flutter team is currently trialing the use of [Gemini Code Assist for GitHub](https://developers.google.com/gemini-code-assist/docs/review-github-code). Comments from the `gemini-code-assist` bot should not be taken as authoritative feedback from the Flutter team. If you find its comments useful you can update your code accordingly, but if you are unsure or disagree with the feedback, please feel free to wait for a Flutter team member's review for guidance on which automated comments should be addressed.  [Contributor Guide]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#overview [Tree Hygiene]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md [test-exempt]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#tests [Flutter Style Guide]: https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md [Features we expect every widget to implement]: https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md#features-we-expect-every-widget-to-implement [CLA]: https://cla.developers.google.com/ [flutter/tests]: https://github.com/flutter/tests [breaking change policy]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#handling-breaking-changes [Discord]: https://github.com/flutter/flutter/blob/main/docs/contributing/Chat.md [Data Driven Fixes]: https://github.com/flutter/flutter/blob/main/docs/contributing/Data-driven-Fixes.md

[Impeller] include uniform info in impellerc json reflections

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github-actions bot added engine flutter/engine related. See also e: labels. e: impeller Impeller rendering backend issues and features requests labels Dec 2, 2025

fix unit tests

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flar commented Dec 4, 2025

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flar added 2 commits December 3, 2025 17:36

only run SkSL specific tests on SkSL target

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Merge remote-tracking branch 'upstream/master' into impellerc-uniform…

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…-json-output

flar marked this pull request as ready for review December 4, 2025 03:04

flar requested a review from chinmaygarde December 4, 2025 03:04

simplify unit tests and add positioned uniforms test

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flar commented Dec 4, 2025

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flar mentioned this pull request Dec 4, 2025

[Impeller] reflector.cc causes unnecessary copies #179434

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flar added the autosubmit Merge PR when tree becomes green via auto submit App label Dec 4, 2025

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Merged via the queue into flutter:master with commit 4d76229 Dec 5, 2025
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Roll Flutter from 69d8710fadcd to 144af688e082 (41 revisions) flutter/packages#10572

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4d7622947 [Impeller] include uniform info in impellerc json reflectio…

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…ns (flutter/flutter#179317)

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Roll Flutter from 69d8710fadcd to 5b8720312a94 (42 revisions) flutter/packages#10574

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4d7622947 [Impeller] include uniform info in impellerc json reflectio…

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…ns (flutter/flutter#179317)

[Impeller] include uniform info in impellerc json reflections #179317

[Impeller] include uniform info in impellerc json reflections #179317

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flar commented Dec 2, 2025

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