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

5 files changed, 58 insertions, 45 deletions

diff --git a/src/gui/painting/qpainter.cpp b/src/gui/painting/qpainter.cpp
index 657229a481..4596754d57 100644
--- a/src/gui/painting/qpainter.cpp
+++ b/src/gui/painting/qpainter.cpp
@@ -5855,14 +5855,24 @@ void QPainter::drawStaticText(const QPointF &topLeftPosition, const QStaticText
         return;
     }
 
+    if (d->extended->type() == QPaintEngine::OpenGL2 && !staticText_d->untransformedCoordinates) {
+        staticText_d->untransformedCoordinates = true;
+        staticText_d->needsRelayout = true;
+    } else if (d->extended->type() != QPaintEngine::OpenGL2 && staticText_d->untransformedCoordinates) {
+        staticText_d->untransformedCoordinates = false;
+        staticText_d->needsRelayout = true;
+    }
+
     // Don't recalculate entire layout because of translation, rather add the dx and dy
     // into the position to move each text item the correct distance.
-    QPointF transformedPosition = topLeftPosition * d->state->matrix;
-    QTransform matrix = d->state->matrix;
+    QPointF transformedPosition = topLeftPosition;
+    if (!staticText_d->untransformedCoordinates)
+        transformedPosition = transformedPosition * d->state->matrix;
+    QTransform oldMatrix;
 
     // The translation has been applied to transformedPosition. Remove translation
     // component from matrix.
-    if (d->state->matrix.isTranslating()) {
+    if (d->state->matrix.isTranslating() && !staticText_d->untransformedCoordinates) {
         qreal m11 = d->state->matrix.m11();
         qreal m12 = d->state->matrix.m12();
         qreal m13 = d->state->matrix.m13();
@@ -5871,6 +5881,7 @@ void QPainter::drawStaticText(const QPointF &topLeftPosition, const QStaticText
         qreal m23 = d->state->matrix.m23();
         qreal m33 = d->state->matrix.m33();
 
+        oldMatrix = d->state->matrix;
         d->state->matrix.setMatrix(m11, m12, m13,
                                    m21, m22, m23,
                                    0.0, 0.0, m33);
@@ -5879,7 +5890,7 @@ void QPainter::drawStaticText(const QPointF &topLeftPosition, const QStaticText
     // If the transform is not identical to the text transform,
     // we have to relayout the text (for other transformations than plain translation)
     bool staticTextNeedsReinit = staticText_d->needsRelayout;
-    if (staticText_d->matrix != d->state->matrix) {
+    if (!staticText_d->untransformedCoordinates && staticText_d->matrix != d->state->matrix) {
         staticText_d->matrix = d->state->matrix;
         staticTextNeedsReinit = true;
     }
@@ -5918,8 +5929,8 @@ void QPainter::drawStaticText(const QPointF &topLeftPosition, const QStaticText
     if (currentColor != oldPen.color())
         setPen(oldPen);
 
-    if (matrix.isTranslating())
-        d->state->matrix = matrix;
+    if (!staticText_d->untransformedCoordinates && oldMatrix.isTranslating())
+        d->state->matrix = oldMatrix;
 }
 
 /*!
diff --git a/src/gui/text/qstatictext.cpp b/src/gui/text/qstatictext.cpp
index 84c1d96735..10870aa0cb 100644
--- a/src/gui/text/qstatictext.cpp
+++ b/src/gui/text/qstatictext.cpp
@@ -115,10 +115,12 @@ QT_BEGIN_NAMESPACE
     Qt::RichText.
 
     If it's the first time the static text is drawn, or if the static text, or the painter's font
-    or matrix have been altered since the last time it was drawn, the text's layout has to be
-    recalculated. This will impose an overhead on the QPainter::drawStaticText() call where the
-    relayout occurs. To avoid this overhead in the paint event, you can call prepare() ahead of
-    time to ensure that the layout is calculated.
+    has been altered since the last time it was drawn, the text's layout has to be
+    recalculated. On some paint engines, changing the matrix of the painter will also cause the
+    layout to be recalculated. In particular, this will happen for any engine except for the
+    OpenGL2 paint engine. Recalculating the layout will impose an overhead on the
+    QPainter::drawStaticText() call where it occurs. To avoid this overhead in the paint event, you
+    can call prepare() ahead of time to ensure that the layout is calculated.
 
     \sa QPainter::drawText(), QPainter::drawStaticText(), QTextLayout, QTextDocument
 */
@@ -188,8 +190,9 @@ void QStaticText::detach()
 
   When drawStaticText() is called, the layout of the QStaticText will be recalculated if any part
   of the QStaticText object has changed since the last time it was drawn. It will also be
-  recalculated if the painter's font or matrix are not the same as when the QStaticText was last
-  drawn.
+  recalculated if the painter's font is not the same as when the QStaticText was last drawn, or,
+  on any other paint engine than the OpenGL2 engine, if the painter's matrix has been altered
+  since the static text was last drawn.
 
   To avoid the overhead of creating the layout the first time you draw the QStaticText after
   making changes, you can use the prepare() function and pass in the \a matrix and \a font you
@@ -364,14 +367,16 @@ QSizeF QStaticText::size() const
 
 QStaticTextPrivate::QStaticTextPrivate()
         : textWidth(-1.0), items(0), itemCount(0), glyphPool(0), positionPool(0), charPool(0),
-          needsRelayout(true), useBackendOptimizations(false), textFormat(Qt::AutoText)
+          needsRelayout(true), useBackendOptimizations(false), textFormat(Qt::AutoText),
+          untransformedCoordinates(false)
 {
 }
 
 QStaticTextPrivate::QStaticTextPrivate(const QStaticTextPrivate &other)
     : text(other.text), font(other.font), textWidth(other.textWidth), matrix(other.matrix),
       items(0), itemCount(0), glyphPool(0), positionPool(0), charPool(0), needsRelayout(true),
-      useBackendOptimizations(other.useBackendOptimizations), textFormat(other.textFormat)
+      useBackendOptimizations(other.useBackendOptimizations), textFormat(other.textFormat),
+      untransformedCoordinates(other.untransformedCoordinates)
 {
 }
 
@@ -396,8 +401,9 @@ namespace {
     class DrawTextItemRecorder: public QPaintEngine
     {
     public:
-        DrawTextItemRecorder(bool useBackendOptimizations, int numChars)
-                : m_dirtyPen(false), m_useBackendOptimizations(useBackendOptimizations)
+        DrawTextItemRecorder(bool untransformedCoordinates, bool useBackendOptimizations, int numChars)
+                : m_dirtyPen(false), m_useBackendOptimizations(useBackendOptimizations),
+                  m_untransformedCoordinates(untransformedCoordinates)
         {
         }
 
@@ -423,7 +429,7 @@ namespace {
             if (m_dirtyPen)
                 currentItem.color = state->pen().color();
 
-            QTransform matrix = state->transform();
+            QTransform matrix = m_untransformedCoordinates ? QTransform() : state->transform();
             matrix.translate(position.x(), position.y());
 
             QVarLengthArray<glyph_t> glyphs;
@@ -486,14 +492,17 @@ namespace {
 
         bool m_dirtyPen;
         bool m_useBackendOptimizations;
+        bool m_untransformedCoordinates;
     };
 
     class DrawTextItemDevice: public QPaintDevice
     {
     public:
-        DrawTextItemDevice(bool useBackendOptimizations, int numChars)
+        DrawTextItemDevice(bool untransformedCoordinates, bool useBackendOptimizations,
+                           int numChars)
         {
-            m_paintEngine = new DrawTextItemRecorder(useBackendOptimizations, numChars);
+            m_paintEngine = new DrawTextItemRecorder(untransformedCoordinates,
+                                                     useBackendOptimizations, numChars);
         }
 
         ~DrawTextItemDevice()
@@ -629,7 +638,7 @@ void QStaticTextPrivate::init()
 
     position = QPointF(0, 0);
 
-    DrawTextItemDevice device(useBackendOptimizations, text.size());
+    DrawTextItemDevice device(untransformedCoordinates, useBackendOptimizations, text.size());
     {
         QPainter painter(&device);
         painter.setFont(font);
diff --git a/src/gui/text/qstatictext_p.h b/src/gui/text/qstatictext_p.h
index 2ab55796d0..1a962918d5 100644
--- a/src/gui/text/qstatictext_p.h
+++ b/src/gui/text/qstatictext_p.h
@@ -148,9 +148,10 @@ public:
     QFixedPoint *positionPool;           // 4 bytes per text
     QChar *charPool;                     // 4 bytes per text
 
-    unsigned char needsRelayout : 1;
-    unsigned char useBackendOptimizations : 1; // 1 byte per text
-    unsigned char textFormat              : 2;
+    unsigned char needsRelayout            : 1; // 1 byte per text
+    unsigned char useBackendOptimizations  : 1;
+    unsigned char textFormat               : 2;
+    unsigned char untransformedCoordinates : 1;
                                          // ================
                                          // 167 bytes per text
 
diff --git a/src/opengl/gl2paintengineex/qpaintengineex_opengl2.cpp b/src/opengl/gl2paintengineex/qpaintengineex_opengl2.cpp
index 5758b25ad5..ee49a3d00c 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 0a046dc38d..59b90d84c0 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);