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, 3 insertions, 4 deletions

diff --git a/src/plugins/platforms/xcb/qxcbcursor.cpp b/src/plugins/platforms/xcb/qxcbcursor.cpp
index e30cc26313..e51ab85e30 100644
--- a/src/plugins/platforms/xcb/qxcbcursor.cpp
+++ b/src/plugins/platforms/xcb/qxcbcursor.cpp
@@ -633,18 +633,17 @@ void QXcbCursor::queryPointer(QXcbConnection *c, xcb_window_t *rootWin, QPoint *
 
 QPoint QXcbCursor::pos() const
 {
-    const int dpr = int(m_screen->devicePixelRatio());
     QPoint p;
     queryPointer(connection(), 0, &p);
-    return p / dpr;
+    return m_screen->mapFromNative(p);
 }
 
 void QXcbCursor::setPos(const QPoint &pos)
 {
-    const int dpr = int(m_screen->devicePixelRatio());
+    const QPoint xPos = m_screen->mapToNative(pos);
     xcb_window_t root = 0;
     queryPointer(connection(), &root, 0);
-    xcb_warp_pointer(xcb_connection(), XCB_NONE, root, 0, 0, 0, 0, pos.x()*dpr, pos.y()*dpr);
+    xcb_warp_pointer(xcb_connection(), XCB_NONE, root, 0, 0, 0, 0, xPos.x(), xPos.y());
     xcb_flush(xcb_connection());
 }