Bug 1549972 - Use ClientMarginHitTestPoint when checking if the mouse is within a draggable region. r=jmathies

ClientMarginHitTestPoint takes into account the fact that we want a minimum
of kResizableBorderMinSize pixels thickness around the window to trigger
resizing.

Differential Revision: https://phabricator.services.mozilla.com/D30427

--HG--
extra : moz-landing-system : lando

widget/windows/nsWindow.cpp

@@ -615,7 +615,7 @@ nsWindow::nsWindow(bool aIsChildWindow)
   mCachedHitTestPoint.x = 0;
   mCachedHitTestPoint.y = 0;
   mCachedHitTestTime = TimeStamp::Now();
-  mCachedHitTestResult = false;
+  mCachedHitTestResult = 0;
 #ifdef MOZ_XUL
   mTransparencyMode = eTransparencyOpaque;
   memset(&mGlassMargins, 0, sizeof mGlassMargins);
@@ -5312,8 +5312,10 @@ bool nsWindow::ProcessMessage(UINT msg, WPARAM& wParam, LPARAM& lParam,
       break;
 
     case WM_MOUSEMOVE: {
-      mMouseInDraggableArea =
-          WithinDraggableRegion(GET_X_LPARAM(lParam), GET_Y_LPARAM(lParam));
+      LPARAM lParamScreen = lParamToScreen(lParam);
+      mMouseInDraggableArea = WithinDraggableRegion(GET_X_LPARAM(lParamScreen),
+                                                    GET_Y_LPARAM(lParamScreen));
+
       if (!mMousePresent && !sIsInMouseCapture) {
         // First MOUSEMOVE over the client area. Ask for MOUSELEAVE
         TRACKMOUSEEVENT mTrack;
@@ -5328,7 +5330,6 @@ bool nsWindow::ProcessMessage(UINT msg, WPARAM& wParam, LPARAM& lParam,
       // Suppress dispatch of pending events
       // when mouse moves are generated by widget
       // creation instead of user input.
-      LPARAM lParamScreen = lParamToScreen(lParam);
       POINT mp;
       mp.x = GET_X_LPARAM(lParamScreen);
       mp.y = GET_Y_LPARAM(lParamScreen);
@@ -5348,8 +5349,7 @@ bool nsWindow::ProcessMessage(UINT msg, WPARAM& wParam, LPARAM& lParam,
 
     case WM_NCMOUSEMOVE: {
       LPARAM lParamClient = lParamToClient(lParam);
-      if (WithinDraggableRegion(GET_X_LPARAM(lParamClient),
-                                GET_Y_LPARAM(lParamClient))) {
+      if (WithinDraggableRegion(GET_X_LPARAM(lParam), GET_Y_LPARAM(lParam))) {
         // If we noticed the mouse moving in our draggable region, forward the
         // message as a normal WM_MOUSEMOVE.
         SendMessage(mWnd, WM_MOUSEMOVE, 0, lParamClient);
@@ -6163,27 +6163,29 @@ int32_t nsWindow::ClientMarginHitTestPoint(int32_t mx, int32_t my) {
   if (!sIsInMouseCapture && allowContentOverride) {
     POINT pt = {mx, my};
     ::ScreenToClient(mWnd, &pt);
-    if (WithinDraggableRegion(pt.x, pt.y)) {
+
+    if (pt.x == mCachedHitTestPoint.x && pt.y == mCachedHitTestPoint.y &&
+        TimeStamp::Now() - mCachedHitTestTime <
+            TimeDuration::FromMilliseconds(HITTEST_CACHE_LIFETIME_MS)) {
+      return mCachedHitTestResult;
+    }
+
+    mCachedHitTestPoint = {pt.x, pt.y};
+    mCachedHitTestTime = TimeStamp::Now();
+
+    if (mDraggableRegion.Contains(pt.x, pt.y)) {
       testResult = HTCAPTION;
     } else {
       testResult = HTCLIENT;
     }
+    mCachedHitTestResult = testResult;
   }
 
   return testResult;
 }
 
-bool nsWindow::WithinDraggableRegion(int32_t clientX, int32_t clientY) {
-  if (clientX == mCachedHitTestPoint.x && clientY == mCachedHitTestPoint.y &&
-      TimeStamp::Now() - mCachedHitTestTime <
-          TimeDuration::FromMilliseconds(HITTEST_CACHE_LIFETIME_MS)) {
-    return mCachedHitTestResult;
-  }
-  mCachedHitTestPoint = {clientX, clientY};
-  mCachedHitTestTime = TimeStamp::Now();
-
-  mCachedHitTestResult = mDraggableRegion.Contains(clientX, clientY);
-  return mCachedHitTestResult;
+bool nsWindow::WithinDraggableRegion(int32_t screenX, int32_t screenY) {
+  return ClientMarginHitTestPoint(screenX, screenY) == HTCAPTION;
 }
 
 TimeStamp nsWindow::GetMessageTimeStamp(LONG aEventTime) const {

widget/windows/nsWindow.h

@@ -664,7 +664,7 @@ class nsWindow final : public nsWindowBase {
   // Whether we we're created as a child window (aka ChildWindow) or not.
   bool mIsChildWindow : 1;
 
-  bool mCachedHitTestResult;
+  int32_t mCachedHitTestResult;
 
   // The point in time at which the last paint completed. We use this to avoid
   //  painting too rapidly in response to frequent input events.