Source-grep collapsed Phase 1+2 onto a single pass. KWin's own GL paths
use GL_R8 correctly (gltexture.cpp:61, shadowitem.cpp:494). The
glTexImage2D(GL_ALPHA) calls observed in the journal originate from
Qt 6:
- qtbase/src/opengl/qopengltextureglyphcache.cpp:111-117 — text glyph
cache upload path. The #else branch (active when qtbase is built
with QT_CONFIG(opengles2)) unconditionally uses GL_ALPHA, with no
runtime check for ES context major version. Correct on ES 2.x;
broken on ES 3.x where GL_ALPHA is no longer a valid glTexImage2D
internalFormat.
- qtbase/src/gui/rhi/qrhigles2.cpp:1373-1378 — Qt-Quick-RHI sibling.
Same logic, gated only on caps.coreProfile, missing the ES≥3 case.
- qtbase/src/opengl/qopengltextureuploader.cpp:253-257 — QImage→GL
upload path; same shape.
KWin runs an ES 3.2 context on Mali-G52 panfrost (RK3566), Qt picks
GL_ALPHA, mesa returns GL_INVALID_VALUE, every dependent draw errors
at level 0, the compositor's frame-callback path stalls. KWin is the
visible victim because it's the compositor, but the bug is in Qt.
KWIN_PIVOT.md rewritten: the patch series and packaging now target
qt6-base-fourier instead of kwin-fourier. Three small hunks (~3 lines
each), runtime-safe via existing caps.gles + caps.ctxMajor / surface
format majorVersion checks. Upstream landing path: bugreports.qt.io
+ Gerrit change against qtbase dev branch.
marfrit