Speed up QStaticText with affine transformation on GL2 engine

Since the OpenGL2 paint engine supports transforming the prerendered
glyphs rather than rasterizing the glyphs with the transformation
applied, we don't need to recalculate the QStaticText layout whenever
the transformation changes. This means that we can do fast animated
transforms for QStaticText on this paint engine. A quick test yields
something like 100x speed-up on Windows. This also give visually
better results, as we previously would animate the hinting of the
glyphs, thus causing jittering.

The autotest has been updated to reflect the fact that drawText() and
drawStaticText() now go through identical paths on GL, also when
transforms are set on the painter. However, the scale was changed in
one test, because it was so great that drawText() would fall back to
paths. With QStaticText the idea is speed, so you'll get a poor, but
fast result instead, which is better than tricking people.

Reviewed-by: Samuel

2 files changed, 14 insertions, 22 deletions

diff --git a/src/opengl/gl2paintengineex/qpaintengineex_opengl2.cpp b/src/opengl/gl2paintengineex/qpaintengineex_opengl2.cpp
index 5758b25..ee49a3d 100644
--- a/src/opengl/gl2paintengineex/qpaintengineex_opengl2.cpp
+++ b/src/opengl/gl2paintengineex/qpaintengineex_opengl2.cpp
@@ -1333,8 +1333,16 @@ void QGL2PaintEngineEx::drawStaticTextItem(QStaticTextItem *textItem)
     QFontEngineGlyphCache::Type glyphType = textItem->fontEngine->glyphFormat >= 0
                                             ? QFontEngineGlyphCache::Type(textItem->fontEngine->glyphFormat)
                                             : d->glyphCacheType;
+    if (glyphType == QFontEngineGlyphCache::Raster_RGBMask) {
+        if (d->device->alphaRequested() || state()->matrix.type() > QTransform::TxTranslate
+            || (state()->composition_mode != QPainter::CompositionMode_Source
+            && state()->composition_mode != QPainter::CompositionMode_SourceOver))
+        {
+            glyphType = QFontEngineGlyphCache::Raster_A8;
+        }
+    }
 
-    d->drawCachedGlyphs(glyphType, textItem, true);
+    d->drawCachedGlyphs(glyphType, textItem);
 }
 
 bool QGL2PaintEngineEx::drawTexture(const QRectF &dest, GLuint textureId, const QSize &size, const QRectF &src)
@@ -1408,7 +1416,7 @@ void QGL2PaintEngineEx::drawTextItem(const QPointF &p, const QTextItem &textItem
             staticTextItem.numGlyphs = glyphs.size();
             staticTextItem.glyphPositions = positions.data();
 
-            d->drawCachedGlyphs(glyphType, &staticTextItem, false);
+            d->drawCachedGlyphs(glyphType, &staticTextItem);
         }
         return;
     }
@@ -1439,21 +1447,16 @@ namespace {
 // #define QT_OPENGL_DRAWCACHEDGLYPHS_INDEX_ARRAY_VBO
 
 void QGL2PaintEngineExPrivate::drawCachedGlyphs(QFontEngineGlyphCache::Type glyphType,
-                                                QStaticTextItem *staticTextItem,
-                                                bool includeMatrixInCache)
+                                                QStaticTextItem *staticTextItem)
 {
     Q_Q(QGL2PaintEngineEx);
 
     QOpenGL2PaintEngineState *s = q->state();
 
     QGLTextureGlyphCache *cache =
-        (QGLTextureGlyphCache *) staticTextItem->fontEngine->glyphCache(ctx, glyphType,
-                                                                        includeMatrixInCache
-                                                                          ? s->matrix
-                                                                          : QTransform());
+        (QGLTextureGlyphCache *) staticTextItem->fontEngine->glyphCache(ctx, glyphType, QTransform());
     if (!cache || cache->cacheType() != glyphType) {
-        cache = new QGLTextureGlyphCache(ctx, glyphType,
-                                         includeMatrixInCache ? s->matrix : QTransform());
+        cache = new QGLTextureGlyphCache(ctx, glyphType, QTransform());
         staticTextItem->fontEngine->setGlyphCache(ctx, cache);
     }
 
@@ -1561,13 +1564,6 @@ void QGL2PaintEngineExPrivate::drawCachedGlyphs(QFontEngineGlyphCache::Type glyp
     QBrush pensBrush = q->state()->pen.brush();
     setBrush(pensBrush);
 
-    // When painting a QStaticTextItem, the glyph positions are already in device coordinates,
-    // therefore we temporarily set an identity matrix on the painter for the draw call to
-    // avoid transforming the positions twice.
-    QTransform old = s->matrix;
-    if (includeMatrixInCache)
-        s->matrix = QTransform();
-
     if (glyphType == QFontEngineGlyphCache::Raster_RGBMask) {
 
         // Subpixel antialiasing without gamma correction
@@ -1664,9 +1660,6 @@ void QGL2PaintEngineExPrivate::drawCachedGlyphs(QFontEngineGlyphCache::Type glyp
 #else
     glDrawElements(GL_TRIANGLE_STRIP, 6 * staticTextItem->numGlyphs, GL_UNSIGNED_SHORT, elementIndices.data());
 #endif
-
-    if (includeMatrixInCache)
-        s->matrix = old;
 }
 
 void QGL2PaintEngineEx::drawPixmapFragments(const QPainter::PixmapFragment *fragments, int fragmentCount, const QPixmap &pixmap,
diff --git a/src/opengl/gl2paintengineex/qpaintengineex_opengl2_p.h b/src/opengl/gl2paintengineex/qpaintengineex_opengl2_p.h
index 0a046dc..59b90d8 100644
--- a/src/opengl/gl2paintengineex/qpaintengineex_opengl2_p.h
+++ b/src/opengl/gl2paintengineex/qpaintengineex_opengl2_p.h
@@ -202,8 +202,7 @@ public:
     void drawTexture(const QGLRect& dest, const QGLRect& src, const QSize &textureSize, bool opaque, bool pattern = false);
     void drawPixmapFragments(const QPainter::PixmapFragment *fragments, int fragmentCount, const QPixmap &pixmap,
                              QPainter::PixmapFragmentHints hints);
-    void drawCachedGlyphs(QFontEngineGlyphCache::Type glyphType, QStaticTextItem *staticTextItem,
-                          bool includeMatrixInCache);
+    void drawCachedGlyphs(QFontEngineGlyphCache::Type glyphType, QStaticTextItem *staticTextItem);
 
     // Calls glVertexAttributePointer if the pointer has changed
     inline void setVertexAttributePointer(unsigned int arrayIndex, const GLfloat *pointer);