Bug 1370034 - Add nsIWidget::SetWindowOpacity and implement it on Mac. r=spohl

MozReview-Commit-ID: ILqHQuQ4whl

--HG--
extra : rebase_source : 6d45806a0384a58993c425572a8305715df1a181

widget/cocoa/nsCocoaWindow.h

@@ -315,6 +315,7 @@ public:
     virtual nsTransparencyMode GetTransparencyMode() override;
     virtual void SetTransparencyMode(nsTransparencyMode aMode) override;
     virtual void SetWindowShadowStyle(int32_t aStyle) override;
+    virtual void SetWindowOpacity(float aOpacity) override;
     virtual void SetShowsToolbarButton(bool aShow) override;
     virtual void SetShowsFullScreenButton(bool aShow) override;
     virtual void SetWindowAnimationType(WindowAnimationType aType) override;

widget/cocoa/nsCocoaWindow.mm

@@ -2164,6 +2164,20 @@ nsCocoaWindow::SetWindowShadowStyle(int32_t aStyle)
   NS_OBJC_END_TRY_ABORT_BLOCK;
 }
 
+void
+nsCocoaWindow::SetWindowOpacity(float aOpacity)
+{
+  NS_OBJC_BEGIN_TRY_ABORT_BLOCK;
+
+  if (!mWindow) {
+    return;
+  }
+
+  [mWindow setAlphaValue:(CGFloat)aOpacity];
+
+  NS_OBJC_END_TRY_ABORT_BLOCK;
+}
+
 void nsCocoaWindow::SetShowsToolbarButton(bool aShow)
 {
   NS_OBJC_BEGIN_TRY_ABORT_BLOCK;

widget/nsIWidget.h

@@ -1105,6 +1105,14 @@ class nsIWidget : public nsISupports
      */
     virtual void SetWindowShadowStyle(int32_t aStyle) = 0;
 
+    /**
+     * Set the opacity of the window.
+     * Values need to be between 0.0f (invisible) and 1.0f (fully opaque).
+     *
+     * Ignored on child widgets and on non-Mac platforms.
+     */
+    virtual void SetWindowOpacity(float aOpacity) {}
+
     /*
      * On Mac OS X, this method shows or hides the pill button in the titlebar
      * that's used to collapse the toolbar.