Enable glyph cache workaround for Apple M-family of GPUs

Without the workaround, and when using a Core GL profile, we hit a code
path in QSGOpenGLDistanceFieldGlyphCache::resizeTexture() that produced
corrupt glyphs on M1 hardware.

We fix this by enabling the workaround, so that the user doesn't have to
set QT_ENABLE_GLYPH_CACHE_WORKAROUND themselves.

None-Core contexts do not have this problem, but the logic in
QOpenGLContext does not account for recreated contexts with different
formats, so we can't limit the workaround to Core formats only.

With the unified memory architecture of the M1 hardware, the workaround
should have limited negative effects.

In Qt 6 this is not a problem, since Qt Declarative effectively always
uses the workaround code-path, but it's worth recording the fact that
we need the workaround.

Fixes: QTBUG-89379
Change-Id: Icfd8b8b23c0dcda3fea8663d81d0e225134eec5e
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>
(cherry picked from commit aeeaa7d253239b4b45e419bcad5cfde5c5714080)
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

1 files changed, 2 insertions, 1 deletions

diff --git a/src/gui/kernel/qopenglcontext.cpp b/src/gui/kernel/qopenglcontext.cpp
index e8c64bdc01..5124510c0d 100644
--- a/src/gui/kernel/qopenglcontext.cpp
+++ b/src/gui/kernel/qopenglcontext.cpp
@@ -1023,7 +1023,8 @@ bool QOpenGLContext::makeCurrent(QSurface *surface)
                         || qstrcmp(rendererString, "GC800 core") == 0
                         || qstrcmp(rendererString, "GC1000 core") == 0
                         || strstr(rendererString, "GC2000") != 0
-                        || qstrcmp(rendererString, "Immersion.16") == 0;
+                        || qstrcmp(rendererString, "Immersion.16") == 0
+                        || qstrncmp(rendererString, "Apple Mx", 7) == 0;
         }
         needsWorkaroundSet = true;
     }