Bug 1951508 - Move MaybeRoundToDisplayPixels to nsIWidget. r=stransky

No behavior change, but a bit nicer.

Differential Revision: https://phabricator.services.mozilla.com/D240297

Author: emilio

view/nsView.cpp

@@ -205,26 +205,6 @@ bool nsView::IsEffectivelyVisible() {
   return true;
 }
 
-// Cocoa and GTK round widget coordinates to the nearest global "display pixel"
-// integer value. So we avoid fractional display pixel values by rounding to
-// the nearest value that won't yield a fractional display pixel.
-static LayoutDeviceIntRect MaybeRoundToDisplayPixels(
-    const LayoutDeviceIntRect& aRect, TransparencyMode aTransparency,
-    int32_t aRound) {
-  if (aRound == 1) {
-    return aRect;
-  }
-
-  // If the widget doesn't support transparency, we prefer truncating to
-  // ceiling, so that we don't have extra pixels not painted by our frame.
-  auto size = aTransparency == TransparencyMode::Opaque
-                  ? aRect.Size().TruncatedToMultiple(aRound)
-                  : aRect.Size().CeiledToMultiple(aRound);
-  Unused << NS_WARN_IF(aTransparency == TransparencyMode::Opaque &&
-                       size != aRect.Size());
-  return {aRect.TopLeft().RoundedToMultiple(aRound), size};
-}
-
 LayoutDeviceIntRect nsView::CalcWidgetBounds(WindowType aType,
                                              TransparencyMode aTransparency) {
   int32_t p2a = mViewManager->AppUnitsPerDevPixel();
@@ -268,7 +248,8 @@ LayoutDeviceIntRect nsView::CalcWidgetBounds(WindowType aType,
       return idealBounds;
     }
     const int32_t round = widget->RoundsWidgetCoordinatesTo();
-    return MaybeRoundToDisplayPixels(idealBounds, aTransparency, round);
+    return nsIWidget::MaybeRoundToDisplayPixels(idealBounds, aTransparency,
+                                                round);
   }();
 
   // Compute where the top-left of our widget ended up relative to the parent

widget/gtk/nsWindow.cpp

@@ -2044,13 +2044,9 @@ void nsWindow::NativeMoveResizeWaylandPopupCallback(
     GdkPoint parent = WaylandGetParentPosition();
     finalRect.x += parent.x;
     finalRect.y += parent.y;
-    auto roundTo = RoundsWidgetCoordinatesTo();
     auto rect = GdkRectToDevicePixels(finalRect);
-    // Ensure we do the same rounding that nsView would do, see
-    // MaybeRoundToDisplayPixels.
-    auto size = !mIsTransparent ? rect.Size().TruncatedToMultiple(roundTo)
-                                : rect.Size().CeiledToMultiple(roundTo);
-    return LayoutDeviceIntRect(rect.TopLeft().RoundedToMultiple(roundTo), size);
+    // Ensure we do the same rounding that nsView would do.
+    return MaybeRoundToDisplayPixels(rect);
   }();
 
   LOG("  new mBounds [%d, %d] -> [%d x %d]", newBounds.x, newBounds.y,

widget/nsBaseWidget.cpp

@@ -444,6 +444,23 @@ void nsIWidget::RemoveAllChildren() {
   }
 }
 
+LayoutDeviceIntRect nsIWidget::MaybeRoundToDisplayPixels(
+    const LayoutDeviceIntRect& aRect, TransparencyMode aTransparency,
+    int32_t aRound) {
+  if (aRound == 1) {
+    return aRect;
+  }
+
+  // If the widget doesn't support transparency, we prefer truncating to
+  // ceiling, so that we don't have extra pixels not painted by our frame.
+  auto size = aTransparency == TransparencyMode::Opaque
+                  ? aRect.Size().TruncatedToMultiple(aRound)
+                  : aRect.Size().CeiledToMultiple(aRound);
+  Unused << NS_WARN_IF(aTransparency == TransparencyMode::Opaque &&
+                       size != aRect.Size());
+  return {aRect.TopLeft().RoundedToMultiple(aRound), size};
+}
+
 //-------------------------------------------------------------------------
 //
 // Accessor functions to get/set the client data

widget/nsIWidget.h

@@ -983,6 +983,21 @@ class nsIWidget : public nsISupports {
    */
   virtual TransparencyMode GetTransparencyMode() = 0;
 
+  // Cocoa and GTK round widget coordinates to the nearest global "display
+  // pixel" integer value; see bug 892994. So we avoid fractional display pixel
+  // values by rounding to the nearest value that won't yield a fractional
+  // display pixel.
+  virtual int32_t RoundsWidgetCoordinatesTo() { return 1; }
+  static LayoutDeviceIntRect MaybeRoundToDisplayPixels(
+      const LayoutDeviceIntRect& aRect, TransparencyMode aTransparency,
+      int32_t aRound);
+
+  LayoutDeviceIntRect MaybeRoundToDisplayPixels(
+      const LayoutDeviceIntRect& aRect) {
+    return MaybeRoundToDisplayPixels(aRect, GetTransparencyMode(),
+                                     RoundsWidgetCoordinatesTo());
+  }
+
   /**
    * Set the shadow style of the window.
    *
@@ -1953,13 +1968,6 @@ class nsIWidget : public nsISupports {
    */
   virtual bool SynchronouslyRepaintOnResize() { return true; }
 
-  /**
-   * Some platforms (only cocoa right now) round widget coordinates to the
-   * nearest even pixels (see bug 892994), this function allows us to
-   * determine how widget coordinates will be rounded.
-   */
-  virtual int32_t RoundsWidgetCoordinatesTo() { return 1; }
-
   virtual void UpdateZoomConstraints(
       const uint32_t& aPresShellId, const ScrollableLayerGuid::ViewID& aViewId,
       const mozilla::Maybe<ZoomConstraints>& aConstraints) {};