Fixed upside down drawing of accelerated 2d canvas

The convention used by the Qt OpenGL paint engine's internal
drawTexture() function didn't match the texture layout of the
accelerated 2D canvas. We need to adjust the coordinates according to
whether flipped painting is in effect.

Task-number: QTBUG-42376
Change-Id: I787a2deb5f26df532f2e7c475754f0fd2189132c
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@theqtcompany.com>

1 files changed, 10 insertions, 2 deletions

diff --git a/Source/WebCore/platform/graphics/qt/ImageBufferDataQt.cpp b/Source/WebCore/platform/graphics/qt/ImageBufferDataQt.cpp
index a7e60d090..dac6f1bc2 100644
--- a/Source/WebCore/platform/graphics/qt/ImageBufferDataQt.cpp
+++ b/Source/WebCore/platform/graphics/qt/ImageBufferDataQt.cpp
@@ -204,6 +204,11 @@ void ImageBufferDataPrivateAccelerated::draw(GraphicsContext* destContext, Color
 
             QRect rect(QPoint(), m_paintDevice->size());
 
+            // drawTexture's rendering is flipped relative to QtWebKit's convention, so we need to compensate
+            FloatRect srcRectFlipped = m_paintDevice->paintFlipped()
+                ? FloatRect(srcRect.x(), srcRect.maxY(), srcRect.width(), -srcRect.height())
+                : FloatRect(srcRect.x(), rect.height() - srcRect.maxY(), srcRect.width(), srcRect.height());
+
             // Using the same texture as source and target of a rendering operation is undefined in OpenGL,
             // so if that's the case we need to use a temporary intermediate buffer.
             if (m_paintDevice == targetPaintDevice) {
@@ -211,14 +216,17 @@ void ImageBufferDataPrivateAccelerated::draw(GraphicsContext* destContext, Color
 
                 QFramebufferPaintDevice device(rect.size(), QOpenGLFramebufferObject::NoAttachment, false);
 
+                // We disable flipping in order to do a pure blit into the intermediate buffer
+                device.setPaintFlipped(false);
+
                 QPainter painter(&device);
                 QOpenGL2PaintEngineEx* pe = static_cast<QOpenGL2PaintEngineEx*>(painter.paintEngine());
                 pe->drawTexture(rect, m_paintDevice->texture(), rect.size(), rect);
                 painter.end();
 
-                acceleratedPaintEngine->drawTexture(destRect, device.texture(), rect.size(), srcRect);
+                acceleratedPaintEngine->drawTexture(destRect, device.texture(), rect.size(), srcRectFlipped);
             } else {
-                acceleratedPaintEngine->drawTexture(destRect, m_paintDevice->texture(), rect.size(), srcRect);
+                acceleratedPaintEngine->drawTexture(destRect, m_paintDevice->texture(), rect.size(), srcRectFlipped);
             }
 
             return;