Ticket #2782: tab-snap.patch

src/servers/app/Window.h

@@ -251 +251 @@
             void                _ObeySizeLimits();
             void                _PropagatePosition();
 
+            void                _AlterDeltaForSnap(BPoint& delta) const;
+
             BString             fTitle;
             // TODO: no fp rects anywhere
             BRect               fFrame;

src/servers/app/Window.cpp

@@ -1016 +1016 @@
         if (!(Flags() & B_NOT_MOVABLE)) {
             BPoint oldLeftTop = fFrame.LeftTop();
 
+            _AlterDeltaForSnap(delta);
             fDesktop->MoveWindowBy(this, delta.x, delta.y);
 
             // constrain delta to true change in size
@@ -1077 +1078 @@
     }
 }
 
+void
+Window::_AlterDeltaForSnap(BPoint& delta) const
+{
+    // Alter the delta (which is a proposed offset used while dragging a
+    // window) so that the frame of the window 'snaps' to the edges of the
+    // desktop.
 
+    // TODO: preferences to alter this behavior (on/off, snap distance)
+    // TODO: allow user to override this behavior in a reasonable way
+
+    BRect frame = fFrame;
+    BPoint offsetWithinFrame;
+    // TODO: Obtain the usable area (not covered by the tracker)
+    BRect screenFrame = fDesktop->ActiveScreen()->Frame();
+
+    if (fDecorator) {
+        BRegion reg;
+        fDecorator->GetFootprint(&reg);
+        frame = reg.Frame();
+        offsetWithinFrame.x = fFrame.left - frame.left;
+        offsetWithinFrame.y = fFrame.top - frame.top;
+    }
+
+    frame.OffsetBy(delta);
+
+    if (frame.top < screenFrame.top + 4
+        && frame.top > screenFrame.top - 4) {
+        frame.bottom -= frame.top;
+        frame.top = 0;
+    }
+
+    if (frame.left < screenFrame.left + 4
+        && frame.left > screenFrame.left - 4) {
+        frame.right -= frame.left;
+        frame.left = 0;
+    }
+
+    if (frame.bottom > screenFrame.bottom - 4
+        && frame.bottom < screenFrame.bottom + 4) {
+        frame.top -= frame.bottom - screenFrame.bottom;
+        frame.bottom = screenFrame.bottom;
+    }
+
+    if (frame.right > screenFrame.right - 4
+        && frame.right < screenFrame.right + 4) {
+        frame.left -= frame.right - screenFrame.right;
+        frame.right = screenFrame.right;
+    }
+
+    frame.top += offsetWithinFrame.y;
+    frame.left += offsetWithinFrame.x;
+
+    delta.y = frame.top - fFrame.top;
+    delta.x = frame.left - fFrame.left;
+}
+
 // #pragma mark -