Fall back to using paths for large fonts in drawStaticText()

QStaticText had an implicit risk which meant you had to make sure the
text size did not grow unreasonably large. This was intended to avoid
hiding the performance impact of using QStaticText for such a purpose,
but it's too inconvenient. Thus, the same fall back as in drawTextItem()
has been introduced. This will also fix a bug recently introduced when
we started using the FT cache to draw static text in the raster engine,
since this will fail for large fonts.

Task-number: QTBUG-19084, QTBUG-19370
Reviewed-by: Jiang Jiang
(cherry picked from commit 0aa9b30432cec3b7f366983f451fc9a7f8f83243)

4 files changed, 68 insertions, 14 deletions

diff --git a/src/gui/painting/qpaintengine_raster.cpp b/src/gui/painting/qpaintengine_raster.cpp
index f0bc0d6027..4f8af488a1 100644
--- a/src/gui/painting/qpaintengine_raster.cpp
+++ b/src/gui/painting/qpaintengine_raster.cpp
@@ -3029,8 +3029,16 @@ void QRasterPaintEngine::drawStaticTextItem(QStaticTextItem *textItem)
     ensurePen();
     ensureState();
 
-    drawCachedGlyphs(textItem->numGlyphs, textItem->glyphs, textItem->glyphPositions,
-                     textItem->fontEngine());
+    QRasterPaintEngineState *s = state();
+
+    QFontEngine *fontEngine = textItem->fontEngine();
+    const qreal pixelSize = fontEngine->fontDef.pixelSize;
+    if (pixelSize * pixelSize * qAbs(s->matrix.determinant()) < 64 * 64) {
+        drawCachedGlyphs(textItem->numGlyphs, textItem->glyphs, textItem->glyphPositions,
+                         fontEngine);
+    } else {
+        QPaintEngineEx::drawStaticTextItem(textItem);
+    }
 }
 
 /*!
diff --git a/src/gui/painting/qpaintengineex.cpp b/src/gui/painting/qpaintengineex.cpp
index bbdf76f0c0..304e5fc486 100644
--- a/src/gui/painting/qpaintengineex.cpp
+++ b/src/gui/painting/qpaintengineex.cpp
@@ -44,6 +44,8 @@
 #include "qstroker_p.h"
 #include "qbezier_p.h"
 #include <private/qpainterpath_p.h>
+#include <private/qfontengine_p.h>
+#include <private/qstatictext_p.h>
 
 #include <qvarlengtharray.h>
 #include <qdebug.h>
@@ -1057,5 +1059,38 @@ Q_GUI_EXPORT QPainterPath qt_painterPathFromVectorPath(const QVectorPath &path)
     return p;
 }
 
+void QPaintEngineEx::drawStaticTextItem(QStaticTextItem *staticTextItem)
+{
+    QPainterPath path;
+#ifndef Q_WS_MAC
+    path.setFillRule(Qt::WindingFill);
+#endif
+
+    if (staticTextItem->numGlyphs == 0)
+        return;
+
+    QFontEngine *fontEngine = staticTextItem->fontEngine();
+    fontEngine->addGlyphsToPath(staticTextItem->glyphs, staticTextItem->glyphPositions,
+                                staticTextItem->numGlyphs, &path, 0);
+    if (!path.isEmpty()) {
+        QPainterState *s = state();
+        QPainter::RenderHints oldHints = s->renderHints;
+        bool changedHints = false;
+        if (bool(oldHints & QPainter::TextAntialiasing)
+            && !bool(fontEngine->fontDef.styleStrategy & QFont::NoAntialias)
+            && !bool(oldHints & QPainter::Antialiasing)) {
+            s->renderHints |= QPainter::Antialiasing;
+            renderHintsChanged();
+            changedHints = true;
+        }
+
+        fill(qtVectorPathForPath(path), staticTextItem->color);
+
+        if (changedHints) {
+            s->renderHints = oldHints;
+            renderHintsChanged();
+        }
+    }
+}
 
 QT_END_NAMESPACE
diff --git a/src/gui/painting/qpaintengineex_p.h b/src/gui/painting/qpaintengineex_p.h
index d12c602372..7d57eee43d 100644
--- a/src/gui/painting/qpaintengineex_p.h
+++ b/src/gui/painting/qpaintengineex_p.h
@@ -202,7 +202,7 @@ public:
 
     virtual void updateState(const QPaintEngineState &state);
 
-    virtual void drawStaticTextItem(QStaticTextItem *) = 0;
+    virtual void drawStaticTextItem(QStaticTextItem *);
 
     virtual void setState(QPainterState *s);
     inline QPainterState *state() { return static_cast<QPainterState *>(QPaintEngine::state); }
diff --git a/src/opengl/gl2paintengineex/qpaintengineex_opengl2.cpp b/src/opengl/gl2paintengineex/qpaintengineex_opengl2.cpp
index 38bd58d91c..3cf8faa086 100644
--- a/src/opengl/gl2paintengineex/qpaintengineex_opengl2.cpp
+++ b/src/opengl/gl2paintengineex/qpaintengineex_opengl2.cpp
@@ -1436,19 +1436,30 @@ void QGL2PaintEngineEx::drawStaticTextItem(QStaticTextItem *textItem)
 
     ensureActive();
 
-    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;
+    QPainterState *s = state();
+    float det = s->matrix.determinant();
+
+    // don't try to cache huge fonts or vastly transformed fonts
+    QFontEngine *fontEngine = textItem->fontEngine();
+    const qreal pixelSize = fontEngine->fontDef.pixelSize;
+    if (pixelSize * pixelSize * qAbs(det) < QT_MAX_CACHED_GLYPH_SIZE * QT_MAX_CACHED_GLYPH_SIZE ||
+        det < 0.25f || det > 4.f) {
+        QFontEngineGlyphCache::Type glyphType = fontEngine->glyphFormat >= 0
+                                                ? QFontEngineGlyphCache::Type(textItem->fontEngine()->glyphFormat)
+                                                : d->glyphCacheType;
+        if (glyphType == QFontEngineGlyphCache::Raster_RGBMask) {
+            if (d->device->alphaRequested() || s->matrix.type() > QTransform::TxTranslate
+                || (s->composition_mode != QPainter::CompositionMode_Source
+                && s->composition_mode != QPainter::CompositionMode_SourceOver))
+            {
+                glyphType = QFontEngineGlyphCache::Raster_A8;
+            }
         }
-    }
 
-    d->drawCachedGlyphs(glyphType, textItem);
+        d->drawCachedGlyphs(glyphType, textItem);
+    } else {
+        QPaintEngineEx::drawStaticTextItem(textItem);
+    }
 }
 
 bool QGL2PaintEngineEx::drawTexture(const QRectF &dest, GLuint textureId, const QSize &size, const QRectF &src)