Optimize QVGPixmapDropShadowFilter by removing colorize step

Previously, the drop shadow was colorizing the incoming
image and then blurring the colorized version.  This change
first blurs the image to an alpha-only VGImage and then uses
that VGImage as a stencil to draw the drop shadow color.

This way, there is only 1 filter step and a draw instead of
2 filter steps and a draw.  The result is to make the performance
of the drop shadow filter almost identical to the blur filter.

Reviewed-by: trustme

3 files changed, 25 insertions, 52 deletions

diff --git a/src/openvg/qpaintengine_vg.cpp b/src/openvg/qpaintengine_vg.cpp
index fdd61ea..da07c1d 100644
--- a/src/openvg/qpaintengine_vg.cpp
+++ b/src/openvg/qpaintengine_vg.cpp
@@ -2872,6 +2872,24 @@ void qt_vg_drawVGImage(QPainter *painter, const QPointF& pos, VGImage vgImg)
     drawVGImage(engine->vgPrivate(), pos, vgImg);
 }
 
+// Used by qpixmapfilter_vg.cpp to draw filtered VGImage's as a stencil.
+void qt_vg_drawVGImageStencil
+    (QPainter *painter, const QPointF& pos, VGImage vgImg, const QBrush& brush)
+{
+    QVGPaintEngine *engine =
+        static_cast<QVGPaintEngine *>(painter->paintEngine());
+
+    QVGPaintEnginePrivate *d = engine->vgPrivate();
+
+    QTransform transform(d->imageTransform);
+    transform.translate(pos.x(), pos.y());
+    d->setTransform(VG_MATRIX_IMAGE_USER_TO_SURFACE, transform);
+
+    d->ensureBrush(brush);
+    d->setImageMode(VG_DRAW_IMAGE_STENCIL);
+    vgDrawImage(vgImg);
+}
+
 void QVGPaintEngine::drawPixmap(const QRectF &r, const QPixmap &pm, const QRectF &sr)
 {
     QPixmapData *pd = pm.pixmapData();
diff --git a/src/openvg/qpixmapfilter_vg.cpp b/src/openvg/qpixmapfilter_vg.cpp
index 3305bbb..8e104db 100644
--- a/src/openvg/qpixmapfilter_vg.cpp
+++ b/src/openvg/qpixmapfilter_vg.cpp
@@ -58,6 +58,8 @@ QVGPixmapConvolutionFilter::~QVGPixmapConvolutionFilter()
 
 extern void qt_vg_drawVGImage
     (QPainter *painter, const QPointF& pos, VGImage vgImg);
+extern void qt_vg_drawVGImageStencil
+    (QPainter *painter, const QPointF& pos, VGImage vgImg, const QBrush& brush);
 
 void QVGPixmapConvolutionFilter::draw
         (QPainter *painter, const QPointF &dest,
@@ -213,8 +215,7 @@ void QVGPixmapColorizeFilter::draw(QPainter *painter, const QPointF &dest, const
 }
 
 QVGPixmapDropShadowFilter::QVGPixmapDropShadowFilter()
-    : QPixmapDropShadowFilter(),
-      firstTime(true)
+    : QPixmapDropShadowFilter()
 {
 }
 
@@ -238,49 +239,11 @@ void QVGPixmapDropShadowFilter::draw(QPainter *painter, const QPointF &dest, con
         return;
 
     QSize size = pd->size();
-    VGImage tmpImage = vgCreateImage
-        (VG_sARGB_8888_PRE, size.width(), size.height(),
-         VG_IMAGE_QUALITY_FASTER);
-    if (tmpImage == VG_INVALID_HANDLE)
-        return;
-
     VGImage dstImage = vgCreateImage
-        (VG_sARGB_8888_PRE, size.width(), size.height(),
+        (VG_A_8, size.width(), size.height(),
          VG_IMAGE_QUALITY_FASTER);
-    if (dstImage == VG_INVALID_HANDLE) {
-        vgDestroyImage(tmpImage);
+    if (dstImage == VG_INVALID_HANDLE)
         return;
-    }
-
-    // Recompute the color matrix if the color has changed.
-    QColor c = color();
-    if (c != prevColor || firstTime) {
-        prevColor = c;
-
-        matrix[0][0] = 0.0f;
-        matrix[0][1] = 0.0f;
-        matrix[0][2] = 0.0f;
-        matrix[0][3] = 0.0f;
-        matrix[1][0] = 0.0f;
-        matrix[1][1] = 0.0f;
-        matrix[1][2] = 0.0f;
-        matrix[1][3] = 0.0f;
-        matrix[2][0] = 0.0f;
-        matrix[2][1] = 0.0f;
-        matrix[2][2] = 0.0f;
-        matrix[2][3] = 0.0f;
-        matrix[3][0] = c.redF();
-        matrix[3][1] = c.greenF();
-        matrix[3][2] = c.blueF();
-        matrix[3][3] = c.alphaF();
-        matrix[4][0] = 0.0f;
-        matrix[4][1] = 0.0f;
-        matrix[4][2] = 0.0f;
-        matrix[4][3] = 0.0f;
-    }
-
-    // Blacken the source image.
-    vgColorMatrix(tmpImage, srcImage, matrix[0]);
 
     // Clamp the radius range.  We divide by 2 because the OpenVG blur
     // is "too blurry" compared to the default raster implementation.
@@ -292,9 +255,7 @@ void QVGPixmapDropShadowFilter::draw(QPainter *painter, const QPointF &dest, con
         radiusF = maxRadius;
 
     // Blur the blackened source image.
-    vgGaussianBlur(dstImage, tmpImage, radiusF, radiusF, VG_TILE_PAD);
-
-    firstTime = false;
+    vgGaussianBlur(dstImage, srcImage, radiusF, radiusF, VG_TILE_PAD);
 
     VGImage child = VG_INVALID_HANDLE;
 
@@ -308,11 +269,10 @@ void QVGPixmapDropShadowFilter::draw(QPainter *painter, const QPointF &dest, con
         child = vgChildImage(dstImage, srect.x(), srect.y(), srect.width(), srect.height());
     }
 
-    qt_vg_drawVGImage(painter, dest + offset(), child);
+    qt_vg_drawVGImageStencil(painter, dest + offset(), child, color());
 
     if(child != dstImage)
         vgDestroyImage(child);
-    vgDestroyImage(tmpImage);
     vgDestroyImage(dstImage);
 
     // Now draw the actual pixmap over the top.
diff --git a/src/openvg/qpixmapfilter_vg_p.h b/src/openvg/qpixmapfilter_vg_p.h
index f79b6c2..efbbc7b 100644
--- a/src/openvg/qpixmapfilter_vg_p.h
+++ b/src/openvg/qpixmapfilter_vg_p.h
@@ -89,11 +89,6 @@ public:
     ~QVGPixmapDropShadowFilter();
 
     void draw(QPainter *p, const QPointF &pos, const QPixmap &px, const QRectF &src) const;
-
-private:
-    mutable VGfloat matrix[5][4];
-    mutable QColor prevColor;
-    mutable bool firstTime;
 };
 
 class Q_OPENVG_EXPORT QVGPixmapBlurFilter : public QPixmapBlurFilter