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upstream-submissions/qt6-base-fourier: bugreports.qt.io draft
Bug-report body for filing the qt6-base-fourier patch series at bugreports.qt.io against QtBase: OpenGL. Captures: - The summary (GL_ALPHA hard-coded for QT_CONFIG(opengles2), spec-violating in OpenGL ES 3.x). - Reproduction steps (any Mali-class hardware running Plasma Wayland + Qt 6, watch the journal for kwin_wayland's GL debug output). - The four affected sites in qtbase (qopengltextureglyphcache.cpp ×2, qrhigles2.cpp, qopengltextureuploader.cpp). - The fix shape and the runtime predicate added by each patch. - Validation context on ohm (RK3566 PineTab2, mainline 6.19, panfrost mesa 26.0.5). - Gerrit submission boilerplate: account setup, per-patch trailers (Bug:, Pick-to:, Change-Id), reviewer suggestions. The patches themselves stay in arch/qt6-base-fourier/ unchanged — the Change-Id and Bug: trailers will be added at submission time once the bug is filed and bugreports.qt.io issues an issue number. The patches are commit-message-ready to upload via git-review master once those trailers land.
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# bugreports.qt.io issue draft
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**Project**: QtBase
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**Component**: OpenGL
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**Affects Version/s**: 6.5, 6.6, 6.7, 6.8, 6.9, 6.10, 6.11, 6.12-dev
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**Severity**: Significant — affects every Qt 6 GLES3 client on
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Mali-class hardware
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**Type**: Bug
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---
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## Summary
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`QOpenGLTextureGlyphCache`, `QRhiGles2::toGlTextureFormat`
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(`RED_OR_ALPHA8` case), and `QOpenGLTextureUploader` (`Format_Alpha8`
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and `Format_Grayscale8` cases) all hard-code `GL_ALPHA` (and
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`GL_LUMINANCE`) as the `glTexImage2D` `internalFormat` when qtbase
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is configured with `QT_CONFIG(opengles2)` (true on every aarch64
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Linux distribution shipping Qt 6). `GL_ALPHA` was deprecated as a
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valid `glTexImage2D` `internalFormat` in OpenGL ES 3.0 (ES 3.0 spec,
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section 3.8.3, table 3.13 — only sized internal formats remain).
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On Mali-class GPUs (mesa panfrost / panthor) under Wayland, KWin
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requests an OpenGL ES 3.2 context. Qt's text-glyph cache upload
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path then runs the `#else` branch with `GL_ALPHA`, mesa returns
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`GL_INVALID_VALUE`, the texture allocation never succeeds, and
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every subsequent `glTexSubImage2D` to that texture errors at
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level 0. KWin's `glDebugMessageCallback` fills the journal with:
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```
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kwin_wayland: 0x4: GL_INVALID_VALUE in glTexImage2D(internalFormat=GL_ALPHA)
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kwin_wayland: 0x4: GL_INVALID_OPERATION in glTexSubImage2D(invalid texture level 0) × N
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```
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…on every text-glyph cache invalidation, every frame, indefinitely.
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## Reproduce
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- Hardware: any Mali-G31 / G52 / G57 / G610 with mesa panfrost or
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panthor on Linux (RK3399 / RK3566 / RK3588 board, Pinebook Pro,
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PineTab2, CoolPi 4 etc.).
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- Software stack: KDE Plasma 6.x Wayland + Qt 6.x built against
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this hardware (any Arch Linux ARM, Debian arm64, Ubuntu arm64
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with Plasma).
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- Trigger: open any Qt 6 application that renders text and watch
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`journalctl --user -u plasma-kwin_wayland.service` (or
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equivalent) for the `glTexImage2D(internalFormat=GL_ALPHA)`
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line. Examples that trigger reliably:
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- `kate` opening any text file
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- `dolphin` listing a directory
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- any system tray icon update
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- any window decoration title-bar redraw
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## Root cause
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Three sites in qtbase 6.x:
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1. `src/opengl/qopengltextureglyphcache.cpp:111-117` —
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`createTextureData()` hard-codes `internalFormat = GL_ALPHA`
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in the `QT_CONFIG(opengles2)` branch.
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2. `src/opengl/qopengltextureglyphcache.cpp:213-217` —
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`load_glyph_image_to_texture()` matching path on glyph reupload.
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3. `src/gui/rhi/qrhigles2.cpp:1373-1378` — `QRhiGles2::toGlTextureFormat`
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`RED_OR_ALPHA8` case is gated only on `caps.coreProfile`, missing
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the ES≥3 disjunct.
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4. `src/opengl/qopengltextureuploader.cpp:253-275` — `Format_Alpha8`
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and `Format_Grayscale8` short-circuit on `context->isOpenGLES()`
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before reaching the existing `TextureSwizzle` fallback.
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## Fix
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Three patches (attached as a series), one per file. Each adds a
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runtime predicate (variations on `caps.gles && caps.ctxMajor >= 3`
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or `ctx->format().majorVersion() >= 3`) so:
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- desktop GL Core profile → `GL_R8` + `GL_RED` (existing behavior)
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- desktop GL Compat profile → `GL_ALPHA` (existing behavior)
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- **OpenGL ES 3.x → `GL_R8` + `GL_RED`** (new behavior; spec-clean)
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- OpenGL ES 2.x → `GL_ALPHA` (preserved)
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Memory layout, swizzle, and shader behavior identical to the
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existing core-profile path. No new dependencies. ~9 net lines
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added across three files.
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## Validation
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Tested on PineTab2 (RK3566 / Mali-G52 / mainline kernel 6.19.10 /
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panfrost mesa 26.0.5 / KDE Plasma 6.6.4 Wayland / Qt 6.11.0
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patched). Before the patches: constant journal stream of
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`GL_INVALID_VALUE` during normal desktop interaction. After the
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patches: zero `GL_INVALID_VALUE` in a fresh-session journal,
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including under heavy text-rendering load.
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Patch series and end-to-end validation context maintained at
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https://github.com/marfrit/fourier under `qt6-base-fourier/`.
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## Patch series
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(Three patches will be uploaded in Gerrit format as a single
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series with a common Change-Id thread.)
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1. `[PATCH 1/3] QOpenGLTextureGlyphCache: pick GL_R8 on OpenGL ES 3.x`
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2. `[PATCH 2/3] QRhiGles2: use GL_R8 for RED_OR_ALPHA8 on OpenGL ES 3.x`
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3. `[PATCH 3/3] QOpenGLTextureUploader: route ES 3.x through TextureSwizzle path`
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---
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# Gerrit submission notes
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(Per Qt's contribution workflow — https://wiki.qt.io/Qt_Contribution_Guidelines)
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## Account setup (one-time)
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1. Create account at https://account.qt.io
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2. Sign Qt's CLA (electronic, takes 5 minutes)
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3. Configure SSH key at https://codereview.qt-project.org
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4. Install `git-review`: `pacman -S git-review` (Arch) or
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`pip install git-review`
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## Per-patch commit-message trailers
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Each patch needs Qt-style trailers below the `Signed-off-by`:
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```
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Bug: QTBUG-XXXXX
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Pick-to: 6.10 6.9 6.8 6.7 6.6 6.5
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Change-Id: <generated by git-review>
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```
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`Bug:` is the issue number from bugreports.qt.io (the issue above,
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once filed). `Pick-to:` requests cherry-picks to LTS branches —
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this fix should backport cleanly to 6.5 (the oldest currently-
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supported Qt 6 LTS).
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`Change-Id:` is auto-generated by `git-review`'s commit-msg hook
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on first push.
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## Push to Gerrit
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```sh
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cd qtbase
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# Apply our 3 patches with `git am`, then:
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git review master # pushes branch to refs/for/dev
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```
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## Reviewers to add
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- Eskil Abrahamsen Blomfeldt — primary glyph-cache reviewer
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- Laszlo Agocs — RHI reviewer
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- Volker Hilsheimer — QtGui maintainer
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