Direct2D QPA: Speed up text rendering

After analysing text drawing performance two things seem to take up most
of the time. The first is font lookup, the second is QVector
initialization.

To address the first point a per paint engine instance font cache is
introduced. At the moment no mechanism exists to clear this cache and
it is unbounded.

To address the second point, we simply switch to using QVarLengthArray
instead of QVector.

In an artificial benchmark that draws text in a tight loop, the first
change raised fps from ~70 to ~100. The second change further raised this
number to ~115 fps.

Change-Id: Iafa25c3e35bc42bd7c1582b0636e721c5193b494
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>

2 files changed, 60 insertions, 53 deletions

diff --git a/src/plugins/platforms/direct2d/qwindowsdirect2dpaintengine.cpp b/src/plugins/platforms/direct2d/qwindowsdirect2dpaintengine.cpp
index 58c30b6eeb..6e8d9b0baf 100644
--- a/src/plugins/platforms/direct2d/qwindowsdirect2dpaintengine.cpp
+++ b/src/plugins/platforms/direct2d/qwindowsdirect2dpaintengine.cpp
@@ -58,7 +58,6 @@
 #include <QtGui/private/qfontengine_p.h>
 #include <QtGui/private/qstatictext_p.h>
 
-#include <wrl.h>
 using Microsoft::WRL::ComPtr;
 
 QT_BEGIN_NAMESPACE
@@ -346,6 +345,8 @@ public:
 
     QPointF currentBrushOrigin;
 
+    QHash< QFont, ComPtr<IDWriteFontFace> > fontCache;
+
     struct {
         bool emulate;
         QPen qpen;
@@ -1291,44 +1292,6 @@ void QWindowsDirect2DPaintEngine::drawPixmap(const QRectF &r,
     }
 }
 
-static ComPtr<IDWriteFontFace> fontFaceFromFontEngine(QFontEngine *fe)
-{
-    ComPtr<IDWriteFontFace> fontFace;
-
-    switch (fe->type()) {
-    case QFontEngine::Win:
-    {
-        QWindowsFontEngine *wfe = static_cast<QWindowsFontEngine *>(fe);
-        QSharedPointer<QWindowsFontEngineData> wfed = wfe->fontEngineData();
-
-        HGDIOBJ oldfont = wfe->selectDesignFont();
-        HRESULT hr = QWindowsDirect2DContext::instance()->dwriteGdiInterop()->CreateFontFaceFromHdc(wfed->hdc, &fontFace);
-        DeleteObject(SelectObject(wfed->hdc, oldfont));
-        if (FAILED(hr))
-            qWarning("%s: Could not create DirectWrite fontface from HDC: %#x", __FUNCTION__, hr);
-
-    }
-        break;
-
-#ifndef QT_NO_DIRECTWRITE
-
-    case QFontEngine::DirectWrite:
-    {
-        QWindowsFontEngineDirectWrite *wfedw = static_cast<QWindowsFontEngineDirectWrite *>(fe);
-        fontFace = wfedw->directWriteFontFace();
-    }
-        break;
-
-#endif // QT_NO_DIRECTWRITE
-
-    default:
-        qWarning("%s: Unknown font engine!", __FUNCTION__);
-        break;
-    }
-
-    return fontFace;
-}
-
 void QWindowsDirect2DPaintEngine::drawStaticTextItem(QStaticTextItem *staticTextItem)
 {
     Q_D(QWindowsDirect2DPaintEngine);
@@ -1340,24 +1303,22 @@ void QWindowsDirect2DPaintEngine::drawStaticTextItem(QStaticTextItem *staticText
     ensurePen();
 
     // If we can't support the current configuration with Direct2D, fall back to slow path
-    // Most common cases are perspective transform and gradient brush as pen
-    if ((state()->transform().isAffine() == false) || d->pen.emulate) {
+    if (emulationRequired(PenEmulation)) {
         QPaintEngineEx::drawStaticTextItem(staticTextItem);
         return;
     }
 
-    ComPtr<IDWriteFontFace> fontFace = fontFaceFromFontEngine(staticTextItem->fontEngine());
+    ComPtr<IDWriteFontFace> fontFace = fontFaceFromFontEngine(staticTextItem->font, staticTextItem->fontEngine());
     if (!fontFace) {
         qWarning("%s: Could not find font - falling back to slow text rendering path.", __FUNCTION__);
         QPaintEngineEx::drawStaticTextItem(staticTextItem);
         return;
     }
 
-    QVector<UINT16> glyphIndices(staticTextItem->numGlyphs);
-    QVector<FLOAT> glyphAdvances(staticTextItem->numGlyphs);
-    QVector<DWRITE_GLYPH_OFFSET> glyphOffsets(staticTextItem->numGlyphs);
+    QVarLengthArray<UINT16> glyphIndices(staticTextItem->numGlyphs);
+    QVarLengthArray<FLOAT> glyphAdvances(staticTextItem->numGlyphs);
+    QVarLengthArray<DWRITE_GLYPH_OFFSET> glyphOffsets(staticTextItem->numGlyphs);
 
-    // XXX Are we generating a lot of cache misses here?
     for (int i = 0; i < staticTextItem->numGlyphs; i++) {
         glyphIndices[i] = UINT16(staticTextItem->glyphs[i]); // Imperfect conversion here
 
@@ -1390,24 +1351,22 @@ void QWindowsDirect2DPaintEngine::drawTextItem(const QPointF &p, const QTextItem
     ensurePen();
 
     // If we can't support the current configuration with Direct2D, fall back to slow path
-    // Most common cases are perspective transform and gradient brush as pen
-    if ((state()->transform().isAffine() == false) || d->pen.emulate) {
+    if (emulationRequired(PenEmulation)) {
         QPaintEngine::drawTextItem(p, textItem);
         return;
     }
 
-    ComPtr<IDWriteFontFace> fontFace = fontFaceFromFontEngine(ti.fontEngine);
+    ComPtr<IDWriteFontFace> fontFace = fontFaceFromFontEngine(*ti.f, ti.fontEngine);
     if (!fontFace) {
         qWarning("%s: Could not find font - falling back to slow text rendering path.", __FUNCTION__);
         QPaintEngine::drawTextItem(p, textItem);
         return;
     }
 
-    QVector<UINT16> glyphIndices(ti.glyphs.numGlyphs);
-    QVector<FLOAT> glyphAdvances(ti.glyphs.numGlyphs);
-    QVector<DWRITE_GLYPH_OFFSET> glyphOffsets(ti.glyphs.numGlyphs);
+    QVarLengthArray<UINT16> glyphIndices(ti.glyphs.numGlyphs);
+    QVarLengthArray<FLOAT> glyphAdvances(ti.glyphs.numGlyphs);
+    QVarLengthArray<DWRITE_GLYPH_OFFSET> glyphOffsets(ti.glyphs.numGlyphs);
 
-    // XXX Are we generating a lot of cache misses here?
     for (int i = 0; i < ti.glyphs.numGlyphs; i++) {
         glyphIndices[i] = UINT16(ti.glyphs.glyphs[i]); // Imperfect conversion here
         glyphAdvances[i] = ti.glyphs.effectiveAdvance(i).toReal();
@@ -1618,4 +1577,49 @@ void QWindowsDirect2DPaintEngine::adjustForAliasing(QPointF *point)
         (*point) += adjustment;
 }
 
+Microsoft::WRL::ComPtr<IDWriteFontFace> QWindowsDirect2DPaintEngine::fontFaceFromFontEngine(const QFont &font, QFontEngine *fe)
+{
+    Q_D(QWindowsDirect2DPaintEngine);
+
+    ComPtr<IDWriteFontFace> fontFace = d->fontCache.value(font);
+    if (fontFace)
+        return fontFace;
+
+    switch (fe->type()) {
+    case QFontEngine::Win:
+    {
+        QWindowsFontEngine *wfe = static_cast<QWindowsFontEngine *>(fe);
+        QSharedPointer<QWindowsFontEngineData> wfed = wfe->fontEngineData();
+
+        HGDIOBJ oldfont = wfe->selectDesignFont();
+        HRESULT hr = QWindowsDirect2DContext::instance()->dwriteGdiInterop()->CreateFontFaceFromHdc(wfed->hdc, &fontFace);
+        DeleteObject(SelectObject(wfed->hdc, oldfont));
+        if (FAILED(hr))
+            qWarning("%s: Could not create DirectWrite fontface from HDC: %#x", __FUNCTION__, hr);
+
+    }
+        break;
+
+#ifndef QT_NO_DIRECTWRITE
+
+    case QFontEngine::DirectWrite:
+    {
+        QWindowsFontEngineDirectWrite *wfedw = static_cast<QWindowsFontEngineDirectWrite *>(fe);
+        fontFace = wfedw->directWriteFontFace();
+    }
+        break;
+
+#endif // QT_NO_DIRECTWRITE
+
+    default:
+        qWarning("%s: Unknown font engine!", __FUNCTION__);
+        break;
+    }
+
+    if (fontFace)
+        d->fontCache.insert(font, fontFace);
+
+    return fontFace;
+}
+
 QT_END_NAMESPACE
diff --git a/src/plugins/platforms/direct2d/qwindowsdirect2dpaintengine.h b/src/plugins/platforms/direct2d/qwindowsdirect2dpaintengine.h
index badd7a7688..fb9b7acec3 100644
--- a/src/plugins/platforms/direct2d/qwindowsdirect2dpaintengine.h
+++ b/src/plugins/platforms/direct2d/qwindowsdirect2dpaintengine.h
@@ -47,6 +47,7 @@
 
 #include <d2d1_1.h>
 #include <dwrite_1.h>
+#include <wrl.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -114,6 +115,8 @@ private:
     bool antiAliasingEnabled() const;
     void adjustForAliasing(QRectF *rect);
     void adjustForAliasing(QPointF *point);
+
+    Microsoft::WRL::ComPtr<IDWriteFontFace> fontFaceFromFontEngine(const QFont &font, QFontEngine *fe);
 };
 
 QT_END_NAMESPACE