Bug 622328 - Limit glass margin adjustments to kGlassMarginAdjustment for frames that hold opaque content. r=roc, a=blocking.

widget/src/windows/nsWindow.cpp

@@ -2649,12 +2649,18 @@ void nsWindow::UpdateGlass()
   DWMNCRENDERINGPOLICY policy = DWMNCRP_USEWINDOWSTYLE;
   switch (mTransparencyMode) {
   case eTransparencyBorderlessGlass:
-    // Only adjust if there is some opaque rectangle
+    // Margins must be 2px (kGlassMarginAdjustment) or larger to cover the 2px
+    // border Windows adds. A value of -1 in cxLeftWidth indicates a sheet of
+    // glass which we ignore here.
     if (margins.cxLeftWidth >= 0) {
-      margins.cxLeftWidth += kGlassMarginAdjustment;
-      margins.cyTopHeight += kGlassMarginAdjustment;
-      margins.cxRightWidth += kGlassMarginAdjustment;
-      margins.cyBottomHeight += kGlassMarginAdjustment;
+      if (margins.cxLeftWidth >= 0 && margins.cxLeftWidth < kGlassMarginAdjustment)
+        margins.cxLeftWidth = kGlassMarginAdjustment;
+      if (margins.cyTopHeight >= 0 && margins.cyTopHeight < kGlassMarginAdjustment)
+        margins.cyTopHeight = kGlassMarginAdjustment;
+      if (margins.cxRightWidth >= 0 && margins.cxRightWidth < kGlassMarginAdjustment)
+        margins.cxRightWidth = kGlassMarginAdjustment;
+      if (margins.cyBottomHeight >= 0 && margins.cyBottomHeight < kGlassMarginAdjustment)
+        margins.cyBottomHeight = kGlassMarginAdjustment;
     }
     // Fall through
   case eTransparencyGlass:
@@ -2662,6 +2668,11 @@ void nsWindow::UpdateGlass()
     break;
   }
 
+  PR_LOG(gWindowsLog, PR_LOG_ALWAYS,
+         ("glass margins: left:%d top:%d right:%d bottom:%d\n",
+          margins.cxLeftWidth, margins.cyTopHeight,
+          margins.cxRightWidth, margins.cyBottomHeight));
+
   // Extends the window frame behind the client area
   if(nsUXThemeData::CheckForCompositor()) {
     nsUXThemeData::dwmExtendFrameIntoClientAreaPtr(hWnd, &margins);