[Impeller] Support instanced rendering in the Impeller HAL. #154145

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1. chinmaygarde

   added

   e: impellerImpeller rendering backend issues and features requestsImpeller rendering backend issues and features requests

   team-engineOwned by Engine teamOwned by Engine team

   on Aug 26, 2024
2. jonahwilliams

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   P3Issues that are less important to the Flutter projectIssues that are less important to the Flutter project

   triaged-engineTriaged by Engine teamTriaged by Engine team

   on Sep 9, 2024
3. gaaclarke commented on Sep 26, 2024

   

   gaaclarke

   on Sep 26, 2024

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   How would we use instancing though? Wouldn't that require some sort of analysis step for the display list to determine what can be instanced, potentially eating any GPU gains with CPU cycles?
4. chinmaygarde commented on Sep 26, 2024

   

   chinmaygarde

   on Sep 26, 2024

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   The impetus for this issue was Flutter GPU. I don't think we necessarily have a use case within the framework where we'd go out of our way to reduce draw calls. The rendering intent there is fairly discordant and doesn't result in that many calls to begin with.

   Hence the lower priority right now. But it might be a fun idea to expose higher level APIs that can take advantage of instancing (for particle systems maybe).

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5. gaaclarke

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   flutter-gpu

   on Sep 26, 2024
6. github-project-automation

   added this to Flutter GPUon Sep 26, 2024
7. github-project-automation

   moved this to 🤔 Needs Triage in Flutter GPUon Sep 26, 2024
8. bdero commented on Sep 26, 2024

   

   bdero

   on Sep 26, 2024

   Last edited by bdero

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   Instancing is basic HAL functionality supported by almost all devices that run Flutter today (> iPhone 6). In the 2D renderer, stuff like glyph sampling or DrawPoints could be made faster by reducing the volume of vertex data that needs to be generated.

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9. bdero commented on Oct 14, 2024

   

   bdero

   on Oct 14, 2024

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   I'm not sure how emulating instancing would work for GLES. gl_InstanceIndex can be used to arbitrarily fetch per-instance data from uniforms, SSBOs, or even Textures. So we'd probably need to get rid of gl_InstanceIndex and lock down per-instance data to a specific managed convention so we can re-write shaders for our emulation, which I'm not sure would be a good idea.

   GLES 3 supports glDrawArraysInstanced/glDrawElementsInstanced. To optionally support instancing in the GLES backend, I think we should also optionally support SSBOs (since we'd be relying on GLES 3 anyways for the feature) and prefer to use those as the backend-independent solution for looking up per-instance data. Other options for binding per-instance data are not really sufficient:

   • Indexing into a uniform array with gl_InstanceIndex would be bad because uniform data is of course very limited.
   • Binding the per-instance data as vertex attributes and using glVertexAttribDivisor isn't great either because it's an exotic GL-ism and I don't think there's a Metal equivalent (there is, however, a Vulkan extension for this with questionable device coverage):

   

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10. bdero commented on Oct 14, 2024

    

    bdero

    on Oct 14, 2024

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    If I compile shaders with GLSL ES 3 for SSBO support, it stops using legacy uniform semantics, so our uniform location lookup routine w/ glGetUniformLocation stops working.

    [ RUN      ] Play/RendererTest.CanRenderPerspectiveCube/OpenGLES
    2024-10-13 23:43:58.529 impeller_unittests[6722:8385232] Metal API Validation Enabled
    2024-10-13 23:43:58.529 impeller_unittests[6722:8385232] Metal GPU Validation Enabled
    ../../flutter/impeller/renderer/backend/gles/buffer_bindings_gles.cc:132: Failure
    Impeller Validation Error
    Could not query the location of an active uniform.
    
    ../../flutter/impeller/renderer/backend/gles/pipeline_library_gles.cc:239: Failure
    Impeller Validation Error
    Could not build pipeline vertex descriptors.
    
    ../../flutter/impeller/renderer/renderer_unittests.cc:189: Failure
    Value of: pipeline
      Actual: false
    Expected: true
    

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11. bdero commented on Oct 15, 2024

    

    bdero

    on Oct 15, 2024

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    W.r.t. Flutter GPU shader compilation for SSBOs and instancing: We can probably have impellerc detect when an SSBO is present and mark the shader as "SSBO supporting" & automatically set a modern GLES version, and then throw a Dart exception if the SSBO cap check fails while loading the shader library (which in this case would be for all GLES, until we can add optional support).

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12. bdero

    moved this from 🤔 Needs Triage to 💡 Features in Flutter GPUon Oct 15, 2024
13. jonahwilliams

    added

    c: new featureNothing broken; request for a new capabilityNothing broken; request for a new capability

    on Apr 2, 2025
14. pull

    added a commit that references this issue on May 28, 2026

    [Impeller] Support instanced rendering across all backends (flutter#1…

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    1d9d637
15. github-merge-queue

    added a commit that references this issue on Jun 6, 2026

    [Flutter GPU] Add instanced draw support (#187359)

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    8a4cca4
16. via-guy

    added 2 commits that reference this issue on Jun 26, 2026

    [Impeller] Support instanced rendering across all backends (flutter#1…

    ...

    7f8a1d5

    [Flutter GPU] Add instanced draw support (flutter#187359)

    ...

    3582b4f