sorry, I couldn't resist...

* added a few very small changes to make the tab sliding work perfectly
* added a comment on the purpose of WindowLayer::fLastMousePosition and
  how it is supposed to be used to have the mouse cursor stick to what
  is being dragged
* TODO: the tab offset doesn't necessarily have to be on [0..1], as long
  as we update it during window resizing to keep the relative position


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@17577 a95241bf-73f2-0310-859d-f6bbb57e9c96

src/servers/app/DefaultDecorator.cpp

@@ -343,11 +343,16 @@ DefaultDecorator::SetTabLocation(float location, BRegion* updateRegion)
 	STRACE(("DefaultDecorator: Set Tab Location(%.1f)\n", location));
 	if (!_tabrect.IsValid())
 		return false;
+
 	if (location < 0)
 		location = 0;
 	if (location > (fRightBorder.right - fLeftBorder.left - _tabrect.Width()))
 		location = (fRightBorder.right - fLeftBorder.left - _tabrect.Width());
+
 	float delta = location - fTabOffset;
+	if (delta == 0.0)
+		return false;
+
 	// redraw old rect (1 pix on the border also must be updated)
 	BRect trect(_tabrect);
 	trect.bottom++;

src/servers/app/Desktop.cpp

@@ -1575,16 +1575,16 @@ Desktop::ResizeWindowBy(WindowLayer* window, float x, float y)
 	UnlockAllWindows();
 }
 
-void
+bool
 Desktop::SetWindowTabLocation(WindowLayer* window, float location)
 {
 	if (!LockAllWindows())
-		return;
+		return false;
 
 	BRegion dirty;
-	window->SetTabLocation(location, dirty);
+	bool changed = window->SetTabLocation(location, dirty);
 
-	if (window->IsVisible() && dirty.CountRects() > 0) {
+	if (changed && window->IsVisible() && dirty.CountRects() > 0) {
 		BRegion stillAvailableOnScreen;
 		_RebuildClippingForAllWindows(stillAvailableOnScreen);
 		_SetBackground(stillAvailableOnScreen);
@@ -1593,6 +1593,8 @@ Desktop::SetWindowTabLocation(WindowLayer* window, float location)
 	}
 
 	UnlockAllWindows();
+
+	return changed;
 }
 
 

src/servers/app/Desktop.h

@@ -111,7 +111,7 @@ class Desktop : public MessageLooper, public ScreenOwner {
 		void					MoveWindowBy(WindowLayer* window, float x, float y,
 									int32 workspace = -1);
 		void					ResizeWindowBy(WindowLayer* window, float x, float y);
-		void					SetWindowTabLocation(WindowLayer* window, float location);
+		bool					SetWindowTabLocation(WindowLayer* window, float location);
 
 		void					SetWindowWorkspaces(WindowLayer* window,
 									uint32 workspaces);

src/servers/app/WindowLayer.cpp

@@ -975,6 +975,14 @@ WindowLayer::MouseMoved(BMessage *message, BPoint where, int32* _viewToken,
 	}
 
 	BPoint delta = where - fLastMousePosition;
+	// NOTE: "delta" is later used to change fLastMousePosition.
+	// If for some reason no change should take effect, delta
+	// is to be set to (0, 0) so that fLastMousePosition is not
+	// adjusted. This way the relative mouse position to the
+	// item being changed (border during resizing, tab during
+	// sliding...) stays fixed when the mouse is moved so that
+	// changes are taking effect again.
+
 	// moving
 	if (fIsDragging) {
 		if (!(Flags() & B_NOT_MOVABLE)) {
@@ -1009,8 +1017,10 @@ WindowLayer::MouseMoved(BMessage *message, BPoint where, int32* _viewToken,
 		float loc = TabLocation();
 		// TODO: change to [0:1]
 		loc += delta.x;
-		fDesktop->SetWindowTabLocation(this, loc);
+		if (fDesktop->SetWindowTabLocation(this, loc))
-		delta.y = 0;
+			delta.y = 0;
+		else
+			delta = BPoint(0, 0);
 	}
 
 	// NOTE: fLastMousePosition is currently only
@@ -1210,7 +1220,7 @@ WindowLayer::SetTabLocation(float location, BRegion& dirty)
 	bool ret = false;
 	if (fDecorator) {
 		ret = fDecorator->SetTabLocation(location, &dirty);
-		fBorderRegionValid = false;
+		fBorderRegionValid = fBorderRegionValid && !ret;
 		// the border very likely changed
 	}
 	return ret;