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

1 files changed, 23 insertions, 14 deletions

diff --git a/src/gui/text/qstatictext.cpp b/src/gui/text/qstatictext.cpp
index 84c1d96..10870aa 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);