[Qt] REGRESSION(r) Two pixel result fail after r153522

https://bugs.webkit.org/show_bug.cgi?id=119392

Reviewed by Jocelyn Turcotte.

Consider scaling transform on the painter to determine final destination size.

Covered by existing tests.

* platform/graphics/qt/ImageQt.cpp:
(WebCore::prescaleImageIfRequired):
(WebCore::BitmapImage::draw):

Change-Id: I631e0925abaf814c95f709c18919f127c8b41503
git-svn-id: http://svn.webkit.org/repository/webkit/trunk@153790 268f45cc-cd09-0410-ab3c-d52691b4dbfc
Reviewed-by: Jocelyn Turcotte <jocelyn.turcotte@digia.com>

1 files changed, 45 insertions, 32 deletions

diff --git a/Source/WebCore/platform/graphics/qt/ImageQt.cpp b/Source/WebCore/platform/graphics/qt/ImageQt.cpp
index 0c66fe5fb..4fb3090fc 100644
--- a/Source/WebCore/platform/graphics/qt/ImageQt.cpp
+++ b/Source/WebCore/platform/graphics/qt/ImageQt.cpp
@@ -42,7 +42,6 @@
 #include <wtf/text/WTFString.h>
 
 #include <QCoreApplication>
-#include <QDebug>
 #include <QImage>
 #include <QImageReader>
 #include <QPainter>
@@ -232,6 +231,49 @@ void BitmapImage::invalidatePlatformData()
 {
 }
 
+QPixmap* prescaleImageIfRequired(QPainter* painter, QPixmap* image, QPixmap* buffer, const QRectF& destRect, QRectF* srcRect)
+{
+    // The quality of down scaling at 0.5x and below in QPainter is not very good
+    // due to using bilinear sampling, so for high quality scaling we need to
+    // perform scaling ourselves.
+    ASSERT(image);
+    ASSERT(painter);
+    if (!(painter->renderHints() & QPainter::SmoothPixmapTransform))
+        return image;
+
+    QTransform transform = painter->combinedTransform();
+
+    // Prescaling transforms that does more than scale or translate is not supported.
+    if (transform.type() > QTransform::TxScale)
+        return image;
+
+    QRectF transformedDst = transform.mapRect(destRect);
+    // Only prescale if downscaling to 0.5x or less
+    if (transformedDst.width() * 2 > srcRect->width() && transformedDst.height() * 2 > srcRect->height())
+        return image;
+
+    // This may not work right with subpixel positions, but that can not currently happen.
+    QRect pixelSrc = srcRect->toRect();
+    QSize scaledSize = transformedDst.size().toSize();
+
+    QString key = QStringLiteral("qtwebkit_prescaled_")
+        % HexString<qint64>(image->cacheKey())
+        % HexString<int>(pixelSrc.x()) % HexString<int>(pixelSrc.y())
+        % HexString<int>(pixelSrc.width()) % HexString<int>(pixelSrc.height())
+        % HexString<int>(scaledSize.width()) % HexString<int>(scaledSize.height());
+
+    if (!QPixmapCache::find(key, buffer)) {
+        if (pixelSrc != image->rect())
+            *buffer = image->copy(pixelSrc).scaled(scaledSize, Qt::IgnoreAspectRatio, Qt::SmoothTransformation);
+        else
+            *buffer = image->scaled(scaledSize, Qt::IgnoreAspectRatio, Qt::SmoothTransformation);
+        QPixmapCache::insert(key, *buffer);
+    }
+
+    *srcRect = QRectF(QPointF(), buffer->size());
+    return buffer;
+}
+
 // Drawing Routines
 void BitmapImage::draw(GraphicsContext* ctxt, const FloatRect& dst,
                        const FloatRect& src, ColorSpace styleColorSpace, CompositeOperator op)
@@ -247,7 +289,6 @@ void BitmapImage::draw(GraphicsContext* ctxt, const FloatRect& dst,
     QPixmap* image = nativeImageForCurrentFrame();
     if (!image)
         return;
-    QPixmap prescaled;
 
     if (mayFillWithSolidColor()) {
         fillWithSolidColor(ctxt, normalizedDst, solidColor(), styleColorSpace, op);
@@ -258,36 +299,8 @@ void BitmapImage::draw(GraphicsContext* ctxt, const FloatRect& dst,
     normalizedSrc = adjustSourceRectForDownSampling(normalizedSrc, image->size());
 #endif
 
-    QPainter* painter = ctxt->platformContext();
-    // The quality of down scaling at 0.5x and below in QPainter is not very good
-    // due only using bilinear sampling, so for high quality scaling we need to
-    // perform scaling ourselves.
-#if QT_VERSION >= QT_VERSION_CHECK(5, 1, 0)
-    const float pixelRatio = painter->device()->devicePixelRatio();
-#else
-    const float pixelRatio = 1;
-#endif
-    if (painter->renderHints() & QPainter::SmoothPixmapTransform
-        && (normalizedDst.width() * 2 * pixelRatio < normalizedSrc.width()
-            || normalizedDst.height() * 2 * pixelRatio < normalizedSrc.height())) {
-        // This may not work right with subpixel positions, but that can not currently happen.
-        QRect pixelSrc = normalizedSrc.toRect();
-        QSize scaledSize(normalizedDst.width() * pixelRatio, normalizedDst.height() * pixelRatio);
-        QString key = QStringLiteral("qtwebkit_prescaled_")
-            % HexString<qint64>(image->cacheKey())
-            % HexString<int>(pixelSrc.x()) % HexString<int>(pixelSrc.y())
-            % HexString<int>(pixelSrc.width()) % HexString<int>(pixelSrc.height())
-            % HexString<int>(scaledSize.width()) % HexString<int>(scaledSize.height());
-        if (!QPixmapCache::find(key, &prescaled)) {
-            if (pixelSrc != image->rect())
-                prescaled = image->copy(pixelSrc).scaled(scaledSize, Qt::IgnoreAspectRatio, Qt::SmoothTransformation);
-            else
-                prescaled = image->scaled(scaledSize, Qt::IgnoreAspectRatio, Qt::SmoothTransformation);
-            QPixmapCache::insert(key, prescaled);
-        }
-        normalizedSrc = QRectF(QPointF(), prescaled.size());
-        image = &prescaled;
-    }
+    QPixmap prescaledBuffer;
+    image = prescaleImageIfRequired(ctxt->platformContext(), image, &prescaledBuffer, normalizedDst, &normalizedSrc);
 
     CompositeOperator previousOperator = ctxt->compositeOperation();
     ctxt->setCompositeOperation(!image->hasAlpha() && op == CompositeSourceOver ? CompositeCopy : op);