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[Impeller][Windows] fix black screen on OpenGL fallback#187288

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Servall4:impeller-fix-opengl-windows
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[Impeller][Windows] fix black screen on OpenGL fallback#187288
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@Servall4 Servall4 commented May 29, 2026 •
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When Impeller is enabled on Windows without Vulkan support, it falls back to OpenGL via ANGLE/D3D11. In this case, compositor_opengl.cc unconditionally called FramebufferTexture2DMultisampleEXT regardless of whether implicit MSAA is supported, causing a fatal GL_INVALID_OPERATION error and a black screen.

embedder.cc already correctly checks SupportsImplicitResolvingMSAA() and creates a non-multisampled texture when implicit MSAA is unavailable. This PR mirrors that check in compositor_opengl.cc, falling back to plain FramebufferTexture2D + RenderbufferStorage while still providing the depth/stencil attachment that Impeller requires.

Fixes #187287

Testing

Manually verified on Windows with ANGLE/D3D11 (no Vulkan, Impeller OpenGL fallback).
Unit tests for this change are not practical because the existing GL mocks in compositor_opengl_unittests.cc map all GL calls to DoNothing, making it impossible to verify correct GL call selection at the driver level.

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@Servall4 Servall4 requested a review from a team as a code owner May 29, 2026 06:11
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flutter-dashboard Bot commented May 29, 2026

It looks like this pull request may not have tests. Please make sure to add tests or get an explicit test exemption before merging.

If you are not sure if you need tests, consider this rule of thumb: the purpose of a test is to make sure someone doesn't accidentally revert the fix. Ask yourself, is there anything in your PR that you feel it is important we not accidentally revert back to how it was before your fix?

Reviewers: Read the Tree Hygiene page and make sure this patch meets those guidelines before LGTMing. If you believe this PR qualifies for a test exemption, contact "@test-exemption-reviewer" in the #hackers channel in Discord (don't just cc them here, they won't see it!). The test exemption team is a small volunteer group, so all reviewers should feel empowered to ask for tests, without delegating that responsibility entirely to the test exemption group.

@github-actions github-actions Bot added engine flutter/engine related. See also e: labels. platform-windows Building on or for Windows specifically a: desktop Running on desktop team-windows Owned by the Windows platform team labels May 29, 2026
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Code Review

This pull request updates the Windows OpenGL compositor to conditionally enable multisample anti-aliasing (MSAA) based on whether the OpenGL context supports implicit MSAA. Feedback indicates that the newly generated depth_stencil renderbuffer is not being deleted or stored, which leads to a GPU resource leak when backing stores are created and destroyed.

Comment thread engine/src/flutter/shell/platform/windows/compositor_opengl.cc Outdated
@Servall4 Servall4 force-pushed the impeller-fix-opengl-windows branch from 21f32d7 to a164303 Compare May 31, 2026 07:34
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loic-sharma reviewed Jun 1, 2026
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Comment thread engine/src/flutter/shell/platform/windows/compositor_opengl.cc
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loic-sharma commented Jun 1, 2026 •
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@Servall4 Is there any unit tests we could add? See: https://github.com/flutter/flutter/blob/master/engine/src/flutter/shell/platform/windows/compositor_opengl_unittests.cc

@gaaclarke would you or someone from the engine team be able to review this change as well?

@loic-sharma loic-sharma added the CICD Run CI/CD label Jun 1, 2026
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@loic-sharma this sounds reasonable to me. I'm unable to test it right now. We do have pretty extensive mocks for opengles that could be used here: https://github.com/flutter/flutter/blob/master/engine/src/flutter/impeller/renderer/backend/gles/test/mock_gles.h

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jason-simmons commented Jun 2, 2026

Confirmed that this fixes #187287 when running with Impeller/GL on my Windows box.

This PR looks good to me.

The APIs defined in the GL_EXT_multisampled_render_to_texture extension should only be called if that extension is present. If it is not available, then the embedder API's MakeRenderTargetFromBackingStoreImpeller will create a non-multisampled texture, so the Windows embedder should configure its backing store accordingly.

The original implementation of Impeller support in Windows CompositorOpenGL assumed that this extension was present. But this regressed when ANGLE removed support for the extension (https://chromium.googlesource.com/angle/angle/+/2207a0a2a151ecb5f016b353242c7e6546951379)

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Servall4 commented Jun 3, 2026

@loic-sharma added, check please

@github-actions github-actions Bot removed the CICD Run CI/CD label Jun 3, 2026
@gaaclarke gaaclarke requested a review from loic-sharma June 3, 2026 21:27
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LGTM, thanks for the wonderful contribution!

@loic-sharma loic-sharma added the CICD Run CI/CD label Jun 3, 2026
@gaaclarke gaaclarke added the autosubmit Merge PR when tree becomes green via auto submit App label Jun 3, 2026
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auto-submit Bot commented Jun 3, 2026

autosubmit label was removed for flutter/flutter/187288, because - The status or check suite Linux linux_host_desktop_engine has failed. Please fix the issues identified (or deflake) before re-applying this label.

@auto-submit auto-submit Bot removed the autosubmit Merge PR when tree becomes green via auto submit App label Jun 3, 2026
@jason-simmons jason-simmons added the autosubmit Merge PR when tree becomes green via auto submit App label Jun 3, 2026
@auto-submit auto-submit Bot added this pull request to the merge queue Jun 4, 2026
Merged via the queue into flutter:master with commit dda3f94 Jun 4, 2026
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2026-06-04 34871572+gmackall@users.noreply.github.com Remove `embedded_android_views_integration_test.dart` (flutter/flutter#187465)
2026-06-04 burak.karahan@mail.ru Remove Material imports from rendering editable tests (flutter/flutter#186951)
2026-06-04 jason-simmons@users.noreply.github.com [Impeller] Wait for the Vulkan device to become idle before destroying Vulkan objects in the AHBSwapchainImplVK destructor (flutter/flutter#187477)
2026-06-04 chris@bracken.jp [iOS] Eliminate unnecessary redeclaration of FlutterDisplayLink (flutter/flutter#187557)
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2026-06-04 jason-simmons@users.noreply.github.com [Impeller] Increase the precision of the IPSampleWithTileModeOES coords parameter to match the input coordinates in the tiled_texture_fill_external shader (flutter/flutter#187545)
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2026-06-04 smille2003@yandex.ru [Impeller][Windows] fix black screen on OpenGL fallback (flutter/flutter#187288)
2026-06-04 97480502+b-luk@users.noreply.github.com Fix unintentionally joined path contours (flutter/flutter#187522)
2026-06-03 matt.boetger@gmail.com fix: resolve issue #177379 by using lazy buildDirectory.dir() API in build.gradle template (flutter/flutter#187127)
2026-06-03 34871572+gmackall@users.noreply.github.com Add a skill for flake analysis (flutter/flutter#187530)
2026-06-03 30870216+gaaclarke@users.noreply.github.com adds linux impeller project flag (flutter/flutter#186982)
2026-06-03 codedoctor@linwood.dev Add support for stylus buttons (flutter/flutter#183369)
2026-06-03 46920873+gabrimatic@users.noreply.github.com Prevent Cubic transform from looping on out-of-range input (flutter/flutter#185875)
2026-06-03 bdero@google.com [Impeller] Reland: Allow attaching specific texture mip levels and slices (flutter/flutter#187470)
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2026-06-03 112751483+shivanshu877@users.noreply.github.com docs: update Impeller advanced blend docs for framebuffer fetch (flutter/flutter#185457)
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[Impeller][Windows] Black screen when Impeller falls back to OpenGL

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