Keep screen geometries from overlapping

The simple mapping of dividing each position by the
devicePixelRatio does not work when screens have different
DPR. If the low-DPR screen above or to the left of the high-DPR
screen, the geometries will overlap in the Qt coordinate system.

This change introduces a new mapping where the origin of each screen
does not move. This mapping is not perfect: it will have gaps between
contiguous screens. However, it will keep non-overlapping screens
non-overlapping in the Qt coordinate system.

Since there is no longer a simple linear coordinate transform, we
have to add screen-dependent mapping functions, and distinguish between
local and non-local coordinates. A side benefit is that the code is
now easier to read, since we remove most manual coordinate transformation.

We also have to cache the screen of each window: since we send resize events
before screen change events, we cannot rely on QPlatformWindow::screen()
(which is set from the screen change event).

Task-number: QTBUG-45076
Change-Id: Ie95a0b71ae274e02903caa102a98af2050a44129
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>

1 files changed, 27 insertions, 2 deletions

diff --git a/src/plugins/platforms/xcb/qxcbscreen.cpp b/src/plugins/platforms/xcb/qxcbscreen.cpp
index fcf70f3c51..bcaa13eb1e 100644
--- a/src/plugins/platforms/xcb/qxcbscreen.cpp
+++ b/src/plugins/platforms/xcb/qxcbscreen.cpp
@@ -273,6 +273,31 @@ QWindow *QXcbScreen::topLevelAt(const QPoint &p) const
     return 0;
 }
 
+
+QPoint QXcbScreen::mapToNative(const QPoint &pos) const
+{
+    const int dpr = int(devicePixelRatio());
+    return (pos - m_geometry.topLeft()) * dpr + m_nativeGeometry.topLeft();
+}
+
+QPoint QXcbScreen::mapFromNative(const QPoint &pos) const
+{
+    const int dpr = int(devicePixelRatio());
+    return (pos - m_nativeGeometry.topLeft()) / dpr + m_geometry.topLeft();
+}
+
+QRect QXcbScreen::mapToNative(const QRect &rect) const
+{
+    const int dpr = int(devicePixelRatio());
+    return QRect(mapToNative(rect.topLeft()), rect.size() * dpr);
+}
+
+QRect QXcbScreen::mapFromNative(const QRect &rect) const
+{
+    const int dpr = int(devicePixelRatio());
+    return QRect(mapFromNative(rect.topLeft()), rect.size() / dpr);
+}
+
 void QXcbScreen::windowShown(QXcbWindow *window)
 {
     // Freedesktop.org Startup Notification
@@ -499,9 +524,9 @@ void QXcbScreen::updateGeometry(const QRect &geom, uint8_t rotation)
     qreal dpi = xGeometry.width() / physicalSize().width() * qreal(25.4);
     m_devicePixelRatio = qRound(dpi/96);
     const int dpr = int(devicePixelRatio()); // we may override m_devicePixelRatio
-    m_geometry = QRect(xGeometry.topLeft()/dpr, xGeometry.size()/dpr);
+    m_geometry = QRect(xGeometry.topLeft(), xGeometry.size()/dpr);
     m_nativeGeometry = QRect(xGeometry.topLeft(), xGeometry.size());
-    m_availableGeometry = QRect(xAvailableGeometry.topLeft()/dpr, xAvailableGeometry.size()/dpr);
+    m_availableGeometry = QRect(mapFromNative(xAvailableGeometry.topLeft()), xAvailableGeometry.size()/dpr);
     QWindowSystemInterface::handleScreenGeometryChange(QPlatformScreen::screen(), m_geometry, m_availableGeometry);
 }