Fix "white line on top and left side of screen" issue

Reproduced on Android, where devices sometimes have screen
sizes which are not evenly dividable by the device scale
factor (see QTBUG-87334 for examples).

Get the surface size for renderSceneGraph() directly from
the QPlatformWindow size. This avoids using the QWindow size,
which might have been rounded and can yield a surface size
which are off by a one or two of pixels.

Also change the "logicalSize" calculation to always use the
size passed to renderSceneGraph(), in order to avoid rounding
errors also here.

Fixes: QTBUG-87334
Change-Id: I23b5784305a876e1ef15ff6b01be09c6ce28409e
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Assam Boudjelthia <assam.boudjelthia@qt.io>

2 files changed, 13 insertions, 11 deletions

diff --git a/src/quick/items/qquickwindow.cpp b/src/quick/items/qquickwindow.cpp
index c6c7b6171e..5d993e4698 100644
--- a/src/quick/items/qquickwindow.cpp
+++ b/src/quick/items/qquickwindow.cpp
@@ -591,15 +591,7 @@ void QQuickWindowPrivate::renderSceneGraph(const QSize &size, const QSize &surfa
                 renderer->setDevicePixelRatio(1);
             }
         } else {
-            QSize pixelSize;
-            QSizeF logicalSize;
-            if (surfaceSize.isEmpty()) {
-                pixelSize = size * devicePixelRatio;
-                logicalSize = size;
-            } else {
-                pixelSize = surfaceSize;
-                logicalSize = QSizeF(surfaceSize) / devicePixelRatio;
-            }
+            const QSize pixelSize = surfaceSize.isEmpty() ? size * devicePixelRatio : surfaceSize;
             QRect rect(QPoint(0, 0), pixelSize);
             renderer->setDeviceRect(rect);
             renderer->setViewportRect(rect);
@@ -607,7 +599,7 @@ void QQuickWindowPrivate::renderSceneGraph(const QSize &size, const QSize &surfa
             QSGAbstractRenderer::MatrixTransformFlags matrixFlags;
             if (flipY)
                 matrixFlags |= QSGAbstractRenderer::MatrixTransformFlipY;
-            renderer->setProjectionMatrixToRect(QRectF(QPoint(0, 0), logicalSize), matrixFlags);
+            renderer->setProjectionMatrixToRect(QRectF(QPoint(0, 0), size), matrixFlags);
             renderer->setDevicePixelRatio(devicePixelRatio);
         }
 
diff --git a/src/quick/scenegraph/qsgthreadedrenderloop.cpp b/src/quick/scenegraph/qsgthreadedrenderloop.cpp
index da0e8bdc7c..457e362b80 100644
--- a/src/quick/scenegraph/qsgthreadedrenderloop.cpp
+++ b/src/quick/scenegraph/qsgthreadedrenderloop.cpp
@@ -368,6 +368,7 @@ public:
 
     QQuickWindow *window; // Will be 0 when window is not exposed
     QSize windowSize;
+    QSize windowPixelSize;
     float dpr = 1;
     int rhiSampleCount = 1;
     bool rhiDeviceLost = false;
@@ -406,6 +407,8 @@ bool QSGRenderThread::event(QEvent *e)
             stopEventProcessing = true;
         window = se->window;
         windowSize = se->size;
+        if (window)
+            windowPixelSize = window->handle()->geometry().size();
         dpr = se->dpr;
 
         pendingUpdate |= SyncRequest;
@@ -833,7 +836,14 @@ void QSGRenderThread::syncAndRender(QImage *grabImage)
         }
     }
     if (current) {
-        d->renderSceneGraph(windowSize, rhi ? cd->swapchain->currentPixelSize() : QSize());
+        const QSize surfaceSize = [this, cd]{
+            if (rhi)
+                return cd->swapchain->currentPixelSize();
+            if (windowPixelSize.isValid())
+                return windowPixelSize;
+            return QSize();
+        }();
+        d->renderSceneGraph(windowSize, surfaceSize);
 
         if (profileFrames)
             renderTime = threadTimer.nsecsElapsed();