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, 9 insertions, 1 deletions

diff --git a/src/plugins/platforms/xcb/qxcbwindow.h b/src/plugins/platforms/xcb/qxcbwindow.h
index c08408a1ca..fbf3cfe172 100644
--- a/src/plugins/platforms/xcb/qxcbwindow.h
+++ b/src/plugins/platforms/xcb/qxcbwindow.h
@@ -155,7 +155,7 @@ public:
     virtual void create();
     virtual void destroy();
     void maybeSetScreen(QXcbScreen *screen);
-    QPlatformScreen *screenForNativeGeometry(const QRect &newGeometry) const;
+    QXcbScreen *screenForNativeGeometry(const QRect &newGeometry) const;
 
 public Q_SLOTS:
     void updateSyncRequestCounter();
@@ -165,6 +165,12 @@ protected:
     virtual void *createVisual() { return Q_NULLPTR; }
     virtual bool supportsSyncProtocol() { return !window()->supportsOpenGL(); }
 
+    QPoint mapToNative(const QPoint &pos, const QXcbScreen *screen) const;
+    QPoint mapFromNative(const QPoint &pos, const QXcbScreen *screen) const;
+    QRect mapToNative(const QRect &rect, const QXcbScreen *screen) const;
+    QRect mapFromNative(const QRect &rect, const QXcbScreen *screen) const;
+    QXcbScreen *parentScreen();
+
     void changeNetWmState(bool set, xcb_atom_t one, xcb_atom_t two = 0);
     NetWmStates netWmStates();
     void setNetWmStates(NetWmStates);
@@ -192,6 +198,8 @@ protected:
 
     xcb_window_t m_window;
 
+    QXcbScreen *m_xcbScreen;
+
     uint m_depth;
     QImage::Format m_imageFormat;
     bool m_imageRgbSwap;