Add work around for bug when painting w/glTexSubImage into large texture

It seems that copying small rectangles from glTexSubImage2D into a
texture which is 2048x2048 is busted on some SGX drivers, even though
the driver reports 2048 as the maximum texture size. This caused text to
turn into flickering garbage once the texture glyph cache had grown to
its max size (e.g. when painting very many Chinese glyphs.) To work
around the problem, we hardcore the maximum texture height to 1024 on
this driver so that the texture glyph cache is reset whenever that
size is exceeded.

Task-number: QT-3971
Done-with: Samuel

4 files changed, 8 insertions, 1 deletions

diff --git a/src/opengl/gl2paintengineex/qtextureglyphcache_gl.cpp b/src/opengl/gl2paintengineex/qtextureglyphcache_gl.cpp
index 1b879c3..ba311c3 100644
--- a/src/opengl/gl2paintengineex/qtextureglyphcache_gl.cpp
+++ b/src/opengl/gl2paintengineex/qtextureglyphcache_gl.cpp
@@ -323,6 +323,9 @@ int QGLTextureGlyphCache::maxTextureWidth() const
 
 int QGLTextureGlyphCache::maxTextureHeight() const
 {
-    return ctx->d_ptr->maxTextureSize();
+    if (ctx->d_ptr->workaround_brokenTexSubImage)
+        return qMin(1024, ctx->d_ptr->maxTextureSize());
+    else
+        return ctx->d_ptr->maxTextureSize();
 }
 QT_END_NAMESPACE
diff --git a/src/opengl/qgl.cpp b/src/opengl/qgl.cpp
index 18f1203..9bf879a 100644
--- a/src/opengl/qgl.cpp
+++ b/src/opengl/qgl.cpp
@@ -1706,6 +1706,7 @@ void QGLContextPrivate::init(QPaintDevice *dev, const QGLFormat &format)
     active_engine = 0;
     workaround_needsFullClearOnEveryFrame = false;
     workaround_brokenFBOReadBack = false;
+    workaround_brokenTexSubImage = false;
     workaroundsCached = false;
 
     workaround_brokenTextureFromPixmap = false;
diff --git a/src/opengl/qgl_egl.cpp b/src/opengl/qgl_egl.cpp
index 8902099..6f9e39c 100644
--- a/src/opengl/qgl_egl.cpp
+++ b/src/opengl/qgl_egl.cpp
@@ -204,6 +204,8 @@ void QGLContext::makeCurrent()
                 const char *egl_version = eglQueryString(d->eglContext->display(), EGL_VERSION);
                 if (egl_version && strstr(egl_version, "1.3"))
                     d->workaround_brokenFBOReadBack = true;
+                else if (egl_version && strstr(egl_version, "1.4"))
+                    d->workaround_brokenTexSubImage = true;
             }
         }
     }
diff --git a/src/opengl/qgl_p.h b/src/opengl/qgl_p.h
index b46d428..bf830ba 100644
--- a/src/opengl/qgl_p.h
+++ b/src/opengl/qgl_p.h
@@ -401,6 +401,7 @@ public:
     // workarounds for driver/hw bugs on different platforms
     uint workaround_needsFullClearOnEveryFrame : 1;
     uint workaround_brokenFBOReadBack : 1;
+    uint workaround_brokenTexSubImage : 1;
     uint workaroundsCached : 1;
 
     uint workaround_brokenTextureFromPixmap : 1;