Canvas: Implement high-DPI render mode

Scale the canvas image and texture buffer by the
target devicePixelRatio.

Task-number: QTBUG-37095
Change-Id: Ic432b278caa5c85cf3487d3108967cf3fcd2fa48
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

1 files changed, 10 insertions, 2 deletions

diff --git a/src/quick/items/context2d/qquickcontext2dtexture.cpp b/src/quick/items/context2d/qquickcontext2dtexture.cpp
index 5ac971dc7d..78c526b299 100644
--- a/src/quick/items/context2d/qquickcontext2dtexture.cpp
+++ b/src/quick/items/context2d/qquickcontext2dtexture.cpp
@@ -538,6 +538,9 @@ QPaintDevice* QQuickContext2DFBOTexture::beginPainting()
 {
     QQuickContext2DTexture::beginPainting();
 
+    const qreal devicePixelRatio = (m_item && m_item->window()) ?
+        m_item->window()->effectiveDevicePixelRatio() : qApp->devicePixelRatio();
+
     if (m_canvasWindow.size().isEmpty()) {
         delete m_fbo;
         delete m_multisampledFbo;
@@ -552,7 +555,7 @@ QPaintDevice* QQuickContext2DFBOTexture::beginPainting()
         delete m_paint_device;
         m_paint_device = 0;
 
-        m_fboSize = npotAdjustedSize(m_canvasWindow.size());
+        m_fboSize = npotAdjustedSize(m_canvasWindow.size() * devicePixelRatio);
         m_canvasWindowChanged = false;
 
         if (doMultisampling()) {
@@ -590,6 +593,7 @@ QPaintDevice* QQuickContext2DFBOTexture::beginPainting()
         QOpenGLPaintDevice *gl_device = new QOpenGLPaintDevice(m_fbo->size());
         gl_device->setPaintFlipped(true);
         gl_device->setSize(m_fbo->size());
+        gl_device->setDevicePixelRatio(devicePixelRatio);
         m_paint_device = gl_device;
     }
 
@@ -694,8 +698,12 @@ QPaintDevice* QQuickContext2DImageTexture::beginPainting()
     if (m_canvasWindow.size().isEmpty())
         return 0;
 
+    const qreal devicePixelRatio = (m_item && m_item->window()) ?
+        m_item->window()->effectiveDevicePixelRatio() : qApp->devicePixelRatio();
+
     if (m_canvasWindowChanged) {
-        m_image = QImage(m_canvasWindow.size(), QImage::Format_ARGB32_Premultiplied);
+        m_image = QImage(m_canvasWindow.size() * devicePixelRatio, QImage::Format_ARGB32_Premultiplied);
+        m_image.setDevicePixelRatio(devicePixelRatio);
         m_image.fill(0x00000000);
         m_canvasWindowChanged = false;
     }