Don't issue GL calls when the geometry is empty

This works as a band-aid and optimization for QT-5104, because in the
text in the example, which contains latin text and has a latin default
font set, will think of all spaces between the cyrillic characters as
latin characters, hence it will make separate text items for them and
issue separate glDrawElements() calls. By cutting off if there are no
glyphs to draw, we can avoid hitting the actual bug for this and several
other use cases, making it less likely to happen.

Task-number: QT-5104
Reviewed-by: Samuel

1 files changed, 2 insertions, 0 deletions

diff --git a/src/opengl/gl2paintengineex/qpaintengineex_opengl2.cpp b/src/opengl/gl2paintengineex/qpaintengineex_opengl2.cpp
index 52450b6..5d2221f 100644
--- a/src/opengl/gl2paintengineex/qpaintengineex_opengl2.cpp
+++ b/src/opengl/gl2paintengineex/qpaintengineex_opengl2.cpp
@@ -1696,6 +1696,8 @@ void QGL2PaintEngineExPrivate::drawCachedGlyphs(QFontEngineGlyphCache::Type glyp
     }
 
     int numGlyphs = vertexCoordinates->vertexCount() / 4;
+    if (numGlyphs == 0)
+        return;
 
     if (elementIndices.size() < numGlyphs*6) {
         Q_ASSERT(elementIndices.size() % 6 == 0);