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Updates GetDartSize to return the number of non-padding bytes#181550

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Updates GetDartSize to return the number of non-padding bytes#181550
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Updates GetDartSize to return the number of non-padding bytes. We used to send uniform information to the FragmentShader code that included the logical size of the uniforms (no padding), after #181340, we started to send the physical size of the uniforms (including padding).

This caused us to mis-represent the size of the uniforms in the FragmentShader API, and possibly caused other issues.

This PR updates GetDartSize to return the number of non-padding bytes (old behavior), and re-enables tests for metal that verify this behavior.

@walley892 walley892 requested a review from gaaclarke January 27, 2026 16:59
@github-actions github-actions Bot added engine flutter/engine related. See also e: labels. e: impeller Impeller rendering backend issues and features requests labels Jan 27, 2026

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Code Review

This pull request correctly updates GetDartSize to return the logical size of uniforms, excluding padding, which resolves an issue in the FragmentShader API. The changes are logical and well-aligned with the goal described, including re-enabling tests for Metal. I've added one suggestion to improve code conciseness.

Comment on lines +14 to +18
for (impeller::RuntimePaddingType byte_type : padding_layout) {
if (byte_type == RuntimePaddingType::kFloat) {
size += sizeof(float);
}
}

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medium

For conciseness, you can use std::count from the <algorithm> header to count the number of float types in padding_layout and calculate the size in a single line. This avoids the explicit loop.

Remember to add #include <algorithm> at the top of the file.

    size = std::count(padding_layout.begin(), padding_layout.end(),
                      impeller::RuntimePaddingType::kFloat) *
           sizeof(float);

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Can we incorporate the reland of #181340 with this pr since it is fixing it?

github-merge-queue Bot pushed a commit that referenced this pull request Jan 28, 2026
Re-landing of #181340
incorporating #181550.

Vec3 uniforms on the metal backend are vec4-aligned. This PR accounts
for that padding.

---------

Co-authored-by: gaaclarke <[email protected]>
@walley892

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Landed as part of #181563

@walley892 walley892 closed this Jan 29, 2026
flutter-zl pushed a commit to flutter-zl/flutter that referenced this pull request Feb 10, 2026
Re-landing of flutter#181340
incorporating flutter#181550.

Vec3 uniforms on the metal backend are vec4-aligned. This PR accounts
for that padding.

---------

Co-authored-by: gaaclarke <[email protected]>
walley892 added a commit to walley892/flutter that referenced this pull request Feb 17, 2026
Re-landing of flutter#181340
incorporating flutter#181550.

Vec3 uniforms on the metal backend are vec4-aligned. This PR accounts
for that padding.

---------

Co-authored-by: gaaclarke <[email protected]>
gaaclarke added a commit to gaaclarke/flutter that referenced this pull request Feb 18, 2026
Reland `Enabled some disabled impeller fragment shader dart tests` (flutter#180788)

relands flutter#180759

changes since revert:
1) waits for async tests now
1) keeps 2 tests that don't pass on impeller disabled

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Enables fragment shader test for impeller (fixes mat2 on vulkan) (flutter#181013)

This rearranges the packing of mat2 fields in structs which was causing
an existing fragment shader test to fail.

The test still doesn't work on Metal, but this PR fixes it for Vulkan. I
suspect the fix for metal may be similar but since the uniforms aren't
in a virtual struct the code isn't hitting this fix.

issue: flutter#180873

- [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
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Account for vec3 padding in Metal (flutter#181563)

Re-landing of flutter#181340
incorporating flutter#181550.

Vec3 uniforms on the metal backend are vec4-aligned. This PR accounts
for that padding.

---------

Co-authored-by: gaaclarke <[email protected]>

Fixes getUniformX for Vulkan (flutter#181286)

Does what it says on the tin!

This PR adds struct member information to the runtime flatbuffer format.
This allows dart code to introspect structs at runtime.

Also modifies the runtime_stage tests to verify formats for all
supported uniform types.

Bubbles up struct member information to dart, and uses that information
to grab struct members in `getUniformX` related functions. This is
necessary on Vulkan because all uniforms are packaged into a single
struct. Also re-enables tests

- [ ] 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.

Organize and update fragment shader uniform tests. (flutter#181822)

Adds more comprehensive testing for setFloat and getUniform* on fragment
shaders.

Deletes redundant tests.

Fixes getUniformVecX indexing errors.

Update web ui fragment shader tests (flutter#181877)

Adds a bunch of tests for uniform setting functionality for custom
fragment shaders on the web.

Deletes redundant tests.

Fixes a discovered issue in the uniform offset calculation. We were
previously using the `location`, which is the integer offset of the
uniform, not the offset in floats.
gaaclarke added a commit to gaaclarke/flutter that referenced this pull request Feb 18, 2026
Reland `Enabled some disabled impeller fragment shader dart tests` (flutter#180788)

relands flutter#180759

changes since revert:
1) waits for async tests now
1) keeps 2 tests that don't pass on impeller disabled

- [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
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Comments from the `gemini-code-assist` bot should not be taken as
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Enables fragment shader test for impeller (fixes mat2 on vulkan) (flutter#181013)

This rearranges the packing of mat2 fields in structs which was causing
an existing fragment shader test to fail.

The test still doesn't work on Metal, but this PR fixes it for Vulkan. I
suspect the fix for metal may be similar but since the uniforms aren't
in a virtual struct the code isn't hitting this fix.

issue: flutter#180873

- [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
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Account for vec3 padding in Metal (flutter#181563)

Re-landing of flutter#181340
incorporating flutter#181550.

Vec3 uniforms on the metal backend are vec4-aligned. This PR accounts
for that padding.

---------

Co-authored-by: gaaclarke <[email protected]>

Fixes getUniformX for Vulkan (flutter#181286)

Does what it says on the tin!

This PR adds struct member information to the runtime flatbuffer format.
This allows dart code to introspect structs at runtime.

Also modifies the runtime_stage tests to verify formats for all
supported uniform types.

Bubbles up struct member information to dart, and uses that information
to grab struct members in `getUniformX` related functions. This is
necessary on Vulkan because all uniforms are packaged into a single
struct. Also re-enables tests

- [ ] 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.

Organize and update fragment shader uniform tests. (flutter#181822)

Adds more comprehensive testing for setFloat and getUniform* on fragment
shaders.

Deletes redundant tests.

Fixes getUniformVecX indexing errors.

Update web ui fragment shader tests (flutter#181877)

Adds a bunch of tests for uniform setting functionality for custom
fragment shaders on the web.

Deletes redundant tests.

Fixes a discovered issue in the uniform offset calculation. We were
previously using the `location`, which is the integer offset of the
uniform, not the offset in floats.
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