Do not always fallback to bitmap printing when printing alpha.

The previous code resulted in that all regions that had some alpha
blending content had to be rasterized as bitmaps.

With this patch, we only need to fallback to proper alpha blending
if there is a background content to blend against.
If there is no background content we simly assume that the background
is white (which happen to be the most common paper color). It will
then be treated as a solid background.

Task-number: QTBUG-33548
Change-Id: I9d2c9be95a701704cdb3724480421db49b4cdd98
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Gunnar Sletta <gunnar.sletta@jollamobile.com>

3 files changed, 35 insertions, 17 deletions

diff --git a/src/printsupport/kernel/qpaintengine_alpha.cpp b/src/printsupport/kernel/qpaintengine_alpha.cpp
index ddfa918b90..ebb1b85e83 100644
--- a/src/printsupport/kernel/qpaintengine_alpha.cpp
+++ b/src/printsupport/kernel/qpaintengine_alpha.cpp
@@ -1,6 +1,6 @@
 /****************************************************************************
 **
-** Copyright (C) 2013 Digia Plc and/or its subsidiary(-ies).
+** Copyright (C) 2014 Digia Plc and/or its subsidiary(-ies).
 ** Contact: http://www.qt-project.org/legal
 **
 ** This file is part of the QtGui module of the Qt Toolkit.
@@ -166,11 +166,14 @@ void QAlphaPaintEngine::drawPath(const QPainterPath &path)
 
     if (d->m_pass == 0) {
         d->m_continueCall = false;
-        if (d->m_hasalpha || d->m_advancedPen || d->m_advancedBrush
+        if (d->canSeeTroughBackground(d->m_hasalpha, tr) || d->m_advancedPen || d->m_advancedBrush
             || d->m_emulateProjectiveTransforms)
         {
             d->addAlphaRect(tr);
         }
+
+        d->addDirtyRect(tr);
+
         if (d->m_picengine)
             d->m_picengine->drawPath(path);
     } else {
@@ -192,12 +195,14 @@ void QAlphaPaintEngine::drawPolygon(const QPointF *points, int pointCount, Polyg
 
     if (d->m_pass == 0) {
         d->m_continueCall = false;
-        if (d->m_hasalpha || d->m_advancedPen || d->m_advancedBrush
+        if (d->canSeeTroughBackground(d->m_hasalpha, tr) || d->m_advancedPen || d->m_advancedBrush
             || d->m_emulateProjectiveTransforms)
         {
             d->addAlphaRect(tr);
         }
 
+        d->addDirtyRect(tr);
+
         if (d->m_picengine)
             d->m_picengine->drawPolygon(points, pointCount, mode);
     } else {
@@ -212,10 +217,12 @@ void QAlphaPaintEngine::drawPixmap(const QRectF &r, const QPixmap &pm, const QRe
     QRectF tr = d->m_transform.mapRect(r);
     if (d->m_pass == 0) {
         d->m_continueCall = false;
-        if (pm.hasAlpha() || d->m_alphaOpacity || d->m_complexTransform || pm.isQBitmap()) {
+        if (d->canSeeTroughBackground(pm.hasAlpha() || d->m_alphaOpacity, tr) || d->m_complexTransform || pm.isQBitmap()) {
             d->addAlphaRect(tr);
         }
 
+        d->addDirtyRect(tr);
+
         if (d->m_picengine)
             d->m_picengine->drawPixmap(r, pm, sr);
 
@@ -233,9 +240,12 @@ void QAlphaPaintEngine::drawTextItem(const QPointF &p, const QTextItem &textItem
 
     if (d->m_pass == 0) {
         d->m_continueCall = false;
-        if (d->m_alphaPen || d->m_alphaOpacity || d->m_advancedPen) {
+        if (d->canSeeTroughBackground(d->m_alphaPen || d->m_alphaOpacity, tr) || d->m_advancedPen) {
             d->addAlphaRect(tr);
         }
+
+        d->addDirtyRect(tr);
+
         if (d->m_picengine) {
             d->m_picengine->drawTextItem(p, textItem);
         }
@@ -252,9 +262,12 @@ void QAlphaPaintEngine::drawTiledPixmap(const QRectF &r, const QPixmap &pixmap,
 
     if (d->m_pass == 0) {
         d->m_continueCall = false;
-        if (pixmap.hasAlpha() || d->m_alphaOpacity || d->m_complexTransform || pixmap.isQBitmap()) {
+        if (d->canSeeTroughBackground(pixmap.hasAlpha() || d->m_alphaOpacity, brect) || d->m_complexTransform || pixmap.isQBitmap()) {
             d->addAlphaRect(brect);
         }
+
+        d->addDirtyRect(brect);
+
         if (d->m_picengine)
             d->m_picengine->drawTiledPixmap(r, pixmap, s);
     } else {
@@ -410,19 +423,14 @@ QRectF QAlphaPaintEnginePrivate::addPenWidth(const QPainterPath &path)
     return (tmp.controlPointRect() * m_transform).boundingRect();
 }
 
-QRect QAlphaPaintEnginePrivate::toRect(const QRectF &rect) const
+void QAlphaPaintEnginePrivate::addAlphaRect(const QRectF &rect)
 {
-    QRect r;
-    r.setLeft(int(rect.left()));
-    r.setTop(int(rect.top()));
-    r.setRight(int(rect.right() + 1));
-    r.setBottom(int(rect.bottom() + 1));
-    return r;
+    m_alphargn |= rect.toAlignedRect();
 }
 
-void QAlphaPaintEnginePrivate::addAlphaRect(const QRectF &rect)
+bool QAlphaPaintEnginePrivate::canSeeTroughBackground(bool somethingInRectHasAlpha, const QRectF &rect) const
 {
-    m_alphargn |= toRect(rect);
+    return somethingInRectHasAlpha && m_dirtyrgn.intersects(rect.toAlignedRect());
 }
 
 void QAlphaPaintEnginePrivate::drawAlphaImage(const QRectF &rect)
@@ -474,7 +482,7 @@ void QAlphaPaintEnginePrivate::drawAlphaImage(const QRectF &rect)
 
 bool QAlphaPaintEnginePrivate::fullyContained(const QRectF &rect) const
 {
-    QRegion r(toRect(rect));
+    QRegion r(rect.toAlignedRect());
     return (m_cliprgn.intersected(r) == r);
 }
 
diff --git a/src/printsupport/kernel/qpaintengine_alpha_p.h b/src/printsupport/kernel/qpaintengine_alpha_p.h
index 8a0781d0d3..d3b10b3d3c 100644
--- a/src/printsupport/kernel/qpaintengine_alpha_p.h
+++ b/src/printsupport/kernel/qpaintengine_alpha_p.h
@@ -107,6 +107,7 @@ public:
 
     QRegion m_alphargn;
     QRegion m_cliprgn;
+    QRegion m_dirtyrgn;
 
     bool m_hasalpha;
     bool m_alphaPen;
@@ -122,6 +123,9 @@ public:
     QPen m_pen;
 
     void addAlphaRect(const QRectF &rect);
+    void addDirtyRect(const QRectF &rect) { m_dirtyrgn |= rect.toAlignedRect(); }
+    bool canSeeTroughBackground(bool somethingInRectHasAlpha, const QRectF &rect) const;
+
     QRectF addPenWidth(const QPainterPath &path);
     void drawAlphaImage(const QRectF &rect);
     QRect toRect(const QRectF &rect) const;
diff --git a/src/printsupport/kernel/qprintengine_win.cpp b/src/printsupport/kernel/qprintengine_win.cpp
index 52b67d162b..8fbf20529c 100644
--- a/src/printsupport/kernel/qprintengine_win.cpp
+++ b/src/printsupport/kernel/qprintengine_win.cpp
@@ -573,7 +573,13 @@ void QWin32PrintEngine::drawPixmap(const QRectF &targetRect,
                 width = (tw - (x * txinc));
             }
 
-            QPixmap p = pixmap.copy(tileSize * x, tileSize * y, imgw, imgh);
+
+            QImage img(QSize(imgw, imgh), QImage::Format_RGB32);
+            img.fill(Qt::white);
+            QPainter painter(&img);
+            painter.drawPixmap(0,0, pixmap, tileSize * x, tileSize * y, imgw, imgh);
+            QPixmap p = QPixmap::fromImage(img);
+
             HBITMAP hbitmap = qt_pixmapToWinHBITMAP(p, HBitmapNoAlpha);
             HDC display_dc = GetDC(0);
             HDC hbitmap_hdc = CreateCompatibleDC(display_dc);