Make rhiFlush() support custom source DPR

The rhiFlush() implementation currently assumes that
QWindow->devicePixelRatio() is the correct scale factor for
transforming device independent window geometry to source geometry.

However, this assumption does not hold if/when we add support
for drawing to a rounded-up DPR, with a downscale later in
the rhiFlush implementation.

Fix this by adding a sourceDevicePixelRatio argument to rhiFlush(),
which is set to either QWindow::devicePixelRatio() or
QWidget::devicePixelRatio(), depending on from where it is used.

Change deviceRect() and friends in qbackingstoredefualtcompositor.cpp
to be scale*() functions instead which take a scale factor instead
of a QWindow. Update call sites to use srouceDevicePixelRatio
where that makes sense.

Pick-to: 6.4
Change-Id: Idb7b1e2f36816a201e00f0defe100d2dc079cb17
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>

5 files changed, 21 insertions, 17 deletions

diff --git a/src/gui/painting/qbackingstoredefaultcompositor.cpp b/src/gui/painting/qbackingstoredefaultcompositor.cpp
index c14efdd42e..949b3bc10a 100644
--- a/src/gui/painting/qbackingstoredefaultcompositor.cpp
+++ b/src/gui/painting/qbackingstoredefaultcompositor.cpp
@@ -129,26 +129,25 @@ QRhiTexture *QBackingStoreDefaultCompositor::toTexture(const QImage &sourceImage
     return m_texture;
 }
 
-static inline QRect deviceRect(const QRect &rect, QWindow *window)
+static inline QRect scaledRect(const QRect &rect, qreal factor)
 {
-    return QRect(rect.topLeft() * window->devicePixelRatio(),
-                 rect.size() * window->devicePixelRatio());
+    return QRect(rect.topLeft() * factor, rect.size() * factor);
 }
 
-static inline QPoint deviceOffset(const QPoint &pt, QWindow *window)
+static inline QPoint scaledOffset(const QPoint &pt, qreal factor)
 {
-    return pt * window->devicePixelRatio();
+    return pt * factor;
 }
 
-static QRegion deviceRegion(const QRegion &region, QWindow *window, const QPoint &offset)
+static QRegion scaledRegion(const QRegion &region, qreal factor, const QPoint &offset)
 {
-    if (offset.isNull() && window->devicePixelRatio() <= 1)
+    if (offset.isNull() && factor <= 1)
         return region;
 
     QVarLengthArray<QRect, 4> rects;
     rects.reserve(region.rectCount());
     for (const QRect &rect : region)
-        rects.append(deviceRect(rect.translated(offset), window));
+        rects.append(scaledRect(rect.translated(offset), factor));
 
     QRegion deviceRegion;
     deviceRegion.setRects(rects.constData(), rects.count());
@@ -236,12 +235,12 @@ static bool prepareDrawForRenderToTextureWidget(const QPlatformTextureList *text
     const QRect clippedRectInWindow = rectInWindow & clipRect.translated(rectInWindow.topLeft());
     const QRect srcRect = toBottomLeftRect(clipRect, rectInWindow.height());
 
-    *target = targetTransform(deviceRect(clippedRectInWindow, window),
+    *target = targetTransform(scaledRect(clippedRectInWindow, window->devicePixelRatio()),
                               deviceWindowRect,
                               invertTargetY);
 
-    *source = sourceTransform(deviceRect(srcRect, window),
-                              deviceRect(rectInWindow, window).size(),
+    *source = sourceTransform(scaledRect(srcRect, window->devicePixelRatio()),
+                              scaledRect(rectInWindow, window->devicePixelRatio()).size(),
                               invertSource ? SourceTransformOrigin::TopLeft : SourceTransformOrigin::BottomLeft);
 
     return true;
@@ -431,6 +430,7 @@ QPlatformBackingStore::FlushResult QBackingStoreDefaultCompositor::flush(QPlatfo
                                                                          QRhi *rhi,
                                                                          QRhiSwapChain *swapchain,
                                                                          QWindow *window,
+                                                                         qreal sourceDevicePixelRatio,
                                                                          const QRegion &region,
                                                                          const QPoint &offset,
                                                                          QPlatformTextureList *textures,
@@ -479,7 +479,7 @@ QPlatformBackingStore::FlushResult QBackingStoreDefaultCompositor::flush(QPlatfo
             const QImage::Format format = QImage::toImageFormat(graphicsBuffer->format());
             const QSize size = graphicsBuffer->size();
             QImage wrapperImage(graphicsBuffer->data(), size.width(), size.height(), graphicsBuffer->bytesPerLine(), format);
-            toTexture(wrapperImage, rhi, resourceUpdates, deviceRegion(region, window, offset), &flags);
+            toTexture(wrapperImage, rhi, resourceUpdates, scaledRegion(region, sourceDevicePixelRatio, offset), &flags);
             gotTextureFromGraphicsBuffer = true;
             graphicsBuffer->unlock();
             if (graphicsBuffer->origin() == QPlatformGraphicsBuffer::OriginBottomLeft)
@@ -487,7 +487,7 @@ QPlatformBackingStore::FlushResult QBackingStoreDefaultCompositor::flush(QPlatfo
         }
     }
     if (!gotTextureFromGraphicsBuffer)
-        toTexture(backingStore, rhi, resourceUpdates, deviceRegion(region, window, offset), &flags);
+        toTexture(backingStore, rhi, resourceUpdates, scaledRegion(region, sourceDevicePixelRatio, offset), &flags);
 
     ensureResources(swapchain, resourceUpdates);
 
@@ -497,8 +497,9 @@ QPlatformBackingStore::FlushResult QBackingStoreDefaultCompositor::flush(QPlatfo
     if (flags & QPlatformBackingStore::TextureFlip)
         origin = SourceTransformOrigin::BottomLeft;
 
-    const QRect deviceWindowRect = deviceRect(QRect(QPoint(), window->size()), window);
-    const QPoint deviceWindowOffset = deviceOffset(offset, window);
+    const qreal dpr = window->devicePixelRatio();
+    const QRect deviceWindowRect = scaledRect(QRect(QPoint(), window->size()), dpr);
+    const QPoint deviceWindowOffset = scaledOffset(offset, dpr);
 
     const bool invertTargetY = rhi->clipSpaceCorrMatrix().data()[5] < 0.0f;
     const bool invertSource = rhi->isYUpInFramebuffer() != rhi->isYUpInNDC();
diff --git a/src/gui/painting/qbackingstoredefaultcompositor_p.h b/src/gui/painting/qbackingstoredefaultcompositor_p.h
index 5086638d2f..d3b91674a6 100644
--- a/src/gui/painting/qbackingstoredefaultcompositor_p.h
+++ b/src/gui/painting/qbackingstoredefaultcompositor_p.h
@@ -37,6 +37,7 @@ public:
                                              QRhi *rhi,
                                              QRhiSwapChain *swapchain,
                                              QWindow *window,
+                                             qreal sourceDevicePixelRatio,
                                              const QRegion &region,
                                              const QPoint &offset,
                                              QPlatformTextureList *textures,
diff --git a/src/gui/painting/qplatformbackingstore.cpp b/src/gui/painting/qplatformbackingstore.cpp
index 74c8ea30ac..befd3a4197 100644
--- a/src/gui/painting/qplatformbackingstore.cpp
+++ b/src/gui/painting/qplatformbackingstore.cpp
@@ -181,13 +181,14 @@ void QPlatformBackingStore::flush(QWindow *window, const QRegion &region, const
     \sa flush()
  */
 QPlatformBackingStore::FlushResult QPlatformBackingStore::rhiFlush(QWindow *window,
+                                                                   qreal sourceDevicePixelRatio,
                                                                    const QRegion &region,
                                                                    const QPoint &offset,
                                                                    QPlatformTextureList *textures,
                                                                    bool translucentBackground)
 {
     return d_ptr->compositor.flush(this, d_ptr->rhiSupport.rhi(), d_ptr->rhiSupport.swapChainForWindow(window),
-                                   window, region, offset, textures, translucentBackground);
+                                   window, sourceDevicePixelRatio, region, offset, textures, translucentBackground);
 }
 
 /*!
diff --git a/src/gui/painting/qplatformbackingstore.h b/src/gui/painting/qplatformbackingstore.h
index bfb40fe5e0..a1bae50555 100644
--- a/src/gui/painting/qplatformbackingstore.h
+++ b/src/gui/painting/qplatformbackingstore.h
@@ -154,6 +154,7 @@ public:
     virtual void flush(QWindow *window, const QRegion &region, const QPoint &offset);
 
     virtual FlushResult rhiFlush(QWindow *window,
+                                 qreal sourceDevicePixelRatio,
                                  const QRegion &region,
                                  const QPoint &offset,
                                  QPlatformTextureList *textures,
diff --git a/src/gui/painting/qrhibackingstore.cpp b/src/gui/painting/qrhibackingstore.cpp
index 71b5ccf6cf..fd7045e3f6 100644
--- a/src/gui/painting/qrhibackingstore.cpp
+++ b/src/gui/painting/qrhibackingstore.cpp
@@ -40,7 +40,7 @@ void QRhiBackingStore::flush(QWindow *window, const QRegion &region, const QPoin
 
     static QPlatformTextureList emptyTextureList;
     bool translucentBackground = m_image.hasAlphaChannel();
-    rhiFlush(window, region, offset, &emptyTextureList, translucentBackground);
+    rhiFlush(window, window->devicePixelRatio(), region, offset, &emptyTextureList, translucentBackground);
 }
 
 QT_END_NAMESPACE