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[Impeller][Vulkan] Explicitly supplied cubemap mip chains are clamped to base mip on Adreno #189965
Description
Steps to reproduce
-
Clone https://github.com/Ram-Dawson/flutter_gpu_manual_mip_repro and use its
mainbranch. -
Use Flutter framework revision
ea1bc5dc4f6fedce69957417b6907e45615146e2, the master revision used for this investigation. -
Run the repro on an Android device using Impeller Vulkan:
flutter pub get flutter run --enable-flutter-gpu -d <device-tcp-serial>
-
Select Cubemap mode and set roughness to
1.00. The app uploads all six faces for each of eight explicitly supplied cubemap mip levels. The color probe requests band 7. -
Select Cubemap mode and set roughness to
0.45. The color probe requests band 3. -
Compare Atlas mode, which represents the same roughness bands without cubemap mip sampling.
The primary affected device is a Redmi K60 Pro (socrates, Adreno 740) on Android 16 / HyperOS OS3.0.303.0. The app startup log reports Impeller Vulkan.
Expected results
The sampler should be able to read the complete manually supplied cubemap mip chain.
At roughness 1.00, the LOD probe requests and should observe gray band 7, and the environment reflection should become diffuse.
At roughness 0.45, the LOD probe requests and should observe green band 3.
Actual results
On Adreno Vulkan, the Cubemap path reads red band 0 at both roughness 1.00 and 0.45. The roughness 1.00 reflection remains overly sharp.
The equivalent Atlas path selects the expected roughness bands. The behavior persists in this standalone Flutter GPU repro, without flutter_scene, a scene graph, directional lights, shadow maps, or a material system.
Code sample
Code sample
The complete minimal reproducible sample is available at https://github.com/Ram-Dawson/flutter_gpu_manual_mip_repro.
main intentionally uses the normal mip-linear sampler against a complete manually supplied cubemap mip chain:
final cubeSampler = gpu.SamplerOptions(
mipFilter: gpu.MipFilter.linear,
);The LOD color probe makes the sampled mip observable rather than relying only on perceived blur. The repository README documents both the baseline and the local-engine patched comparison.
Screenshots or Video
Screenshots / Video demonstration
| Official-engine baseline | Patched local engine | |
|---|---|---|
| Roughness 1.00 visual |  |
 |
| Roughness 1.00 LOD probe |  |
 |
Additional roughness 0.45 LOD probes are in the public repository: baseline, requested band 3 but observed red band 0 and patched, observed green band 3.
Logs
Logs
No Flutter or Dart exception is emitted. The failure is visible in the rendered Cubemap result and the LOD color probe.Flutter Doctor output
Doctor output
The following was collected from the WSL baseline checkout used for reproduction. It intentionally identifies a user branch because this checkout is a locally pinned Flutter source tree. The wireless Android device was not connected to the WSL ADB daemon when this command was collected; the physical-device details used for reproduction are listed above.
[!] Flutter (Channel [user-branch], 3.47.0-1.0.pre-184, on Ubuntu 26.04 LTS 6.18.33.2-microsoft-standard-WSL2, locale C.UTF-8)
! Flutter version 3.47.0-1.0.pre-184 on channel [user-branch] at /home/user01/flutter_engine_ea1bc5dc_baseline
Currently on an unknown channel.
! The flutter binary is not on your path.
! The dart binary is not on your path.
• Upstream repository https://github.com/flutter/flutter.git
• Framework revision ea1bc5dc4f (2026-07-23 02:06:38 +0000)
• Engine revision ea1bc5dc4f
• Dart version 3.14.0 (build 3.14.0-53.0.dev)
• DevTools version 2.60.0
• Feature flags: enable-web, enable-linux-desktop, enable-macos-desktop, enable-windows-desktop, enable-android, enable-ios, cli-animations, enable-native-assets, enable-dart-data-assets, enable-record-use, enable-swift-package-manager, omit-legacy-version-file, enable-lldb-debugging, enable-uiscene-migration, enable-riscv64
[!] Android toolchain - develop for Android devices (Android SDK version 36.0.0)
• Android SDK at /usr/lib/android-sdk
• Emulator version unknown
✗ cmdline-tools component is missing.
✗ Android license status unknown.
[✗] Chrome - develop for the web (Cannot find Chrome executable at google-chrome)
! Cannot find Chrome.
[✗] Linux toolchain - develop for Linux desktop
✗ clang++ is required for Linux development.
✗ CMake is required for Linux development.
• ninja version 1.13.2
• pkg-config version 2.5.1
✗ GTK 3.0 development libraries are required for Linux development.
! Unable to access driver information using 'eglinfo'.
[✓] Connected device (1 available)
• Linux (desktop) • linux • linux-x64 • Ubuntu 26.04 LTS 6.18.33.2-microsoft-standard-WSL2
[✓] Network resources
• All expected network resources are available.
! Doctor found issues in 4 categories.
Activity
puneetkukreja98 commentedon Jul 24, 2026
@Ram-Dawson Thanks for reporting the issue! I tested this on my physical Moto device running Android 16 and got the same results shown under 'official-engine baseline' in the attachment above. Routing this to team-fluttergpu for further investigation.
Update: I ran the application on macOS and the iPhone 17 simulator (iOS 26.5), and the issue does not reproduce there. My actual results on both macOS and iOS match the images under "patched local engine" shown in the report above.
Flutter doctor -v:
Ram-Dawson commentedon Jul 24, 2026
@puneetkukreja98 Thanks for testing. This appears to be specific to Qualcomm Adreno Vulkan devices: Flutter enables a workaround for known automatic mipmap-generation corruption on these drivers, which currently forces sampler LOD to mip 0 even for a complete manually supplied mip chain with explicit textureLod sampling. I reproduced this on Adreno 740, and my patched local engine fixes the car’s over-bright reflections. I opened #189966 for that opt-in manual-mip case; it still needs maintainer review.
gaaclarke commentedon Jul 27, 2026
fyi @bdero