Bug 299748 On listbox, Sometimes, We cannot scroll the page to bottom by mouse wheel r+sr=roc, a=asa

content/events/src/nsEventStateManager.cpp

@@ -1722,21 +1722,11 @@ nsEventStateManager::DoScrollText(nsPresContext* aPresContext,
     scrollView->GetLineHeight(&lineHeight);
 
     if (lineHeight != 0) {
-      nscoord xPos, yPos;
-      scrollView->GetScrollPosition(xPos, yPos);
-
-      if (aNumLines < 0) {
-        passToParent = aScrollHorizontal ? (xPos <= 0) : (yPos <= 0);
-      } else {
-        nsSize scrolledSize;
-        scrollView->GetContainerSize(&scrolledSize.width, &scrolledSize.height);
-
-        nsRect portRect = scrollView->View()->GetBounds();
-
-        passToParent = (aScrollHorizontal ?
-                        (xPos + portRect.width >= scrolledSize.width) :
-                        (yPos + portRect.height >= scrolledSize.height));
-      }
+      PRBool canScroll;
+      nsresult rv = scrollView->CanScroll(aScrollHorizontal,
+                                          (aNumLines > 0), canScroll);
+      if (NS_SUCCEEDED(rv))
+        passToParent = !canScroll;
 
       // Comboboxes need special care.
       nsIComboboxControlFrame* comboBox = nsnull;

view/public/nsIScrollableView.h

@@ -175,6 +175,15 @@ public:
    */
   NS_IMETHOD ScrollByWhole(PRBool aTop) = 0;
 
+  /**
+   * Check the view can scroll from current offset.
+   * @param aHorizontal If checking to Left or to Right, true. Otherwise, false.
+   * @param aForward    If checking to Right or Bottom, true. Otherwise, false.
+   * @param aResult     If the view can scroll, true. Otherwise, false.
+   * @return            error status
+   */
+  NS_IMETHOD CanScroll(PRBool aHorizontal, PRBool aForward, PRBool &aResult) = 0;
+
   /**
    * Returns the view as an nsIView*
    */

view/src/nsScrollPortView.cpp

@@ -468,6 +468,55 @@ NS_IMETHODIMP nsScrollPortView::ScrollByWhole(PRBool aTop)
   return NS_OK;
 }
 
+NS_IMETHODIMP nsScrollPortView::CanScroll(PRBool aHorizontal,
+                                          PRBool aForward,
+                                          PRBool &aResult)
+{
+  nscoord offset = aHorizontal ? mOffsetX : mOffsetY;
+
+  // Can scroll to Top or to Left?
+  if (!aForward) {
+    aResult = (offset > 0) ? PR_TRUE : PR_FALSE;
+    return NS_OK;
+  }
+
+  nsView* scrolledView = GetScrolledView();
+  if (!scrolledView) {
+    aResult = PR_FALSE;
+    return NS_ERROR_FAILURE;
+  }
+
+  nsSize scrolledSize;
+  scrolledView->GetDimensions(scrolledSize);
+
+  nsSize portSize;
+  GetDimensions(portSize);
+
+  nsCOMPtr<nsIDeviceContext> dev;
+  mViewManager->GetDeviceContext(*getter_AddRefs(dev));
+  float t2p, p2t;
+  t2p = dev->AppUnitsToDevUnits();
+  p2t = dev->DevUnitsToAppUnits();
+
+  nscoord max;
+  if (aHorizontal) {
+    max = scrolledSize.width - portSize.width;
+    // Round by pixel
+    nscoord maxPx = NSTwipsToIntPixels(max, t2p);
+    max = NSIntPixelsToTwips(maxPx, p2t);
+  } else {
+    max = scrolledSize.height - portSize.height;
+    // Round by pixel
+    nscoord maxPx = NSTwipsToIntPixels(max, t2p);
+    max = NSIntPixelsToTwips(maxPx, p2t);
+  }
+
+  // Can scroll to Bottom or to Right?
+  aResult = (offset < max) ? PR_TRUE : PR_FALSE;
+
+  return NS_OK;
+}
+
 PRBool nsScrollPortView::CannotBitBlt(nsView* aScrolledView)
 {
   PRUint32  scrolledViewFlags = aScrolledView->GetViewFlags();
@@ -565,16 +614,12 @@ NS_IMETHODIMP nsScrollPortView::ScrollToImpl(nscoord aX, nscoord aY, PRUint32 aU
   PRInt32           dxPx = 0, dyPx = 0;
 
   // convert to pixels
-  nsIDeviceContext  *dev;
-  float             t2p;
-  float             p2t;
-
-  mViewManager->GetDeviceContext(dev);
+  nsCOMPtr<nsIDeviceContext> dev;
+  mViewManager->GetDeviceContext(*getter_AddRefs(dev));
+  float t2p, p2t;
   t2p = dev->AppUnitsToDevUnits();
   p2t = dev->DevUnitsToAppUnits();
 
-  NS_RELEASE(dev);
-
   // Update the scrolled view's position
   nsresult rv = ClampScrollValues(aX, aY, this);
   if (NS_FAILED(rv)) {

view/src/nsScrollPortView.h

@@ -77,6 +77,7 @@ public:
   NS_IMETHOD  GetPageScrollDistances(nsSize *aDistances);
   NS_IMETHOD  ScrollByPages(PRInt32 aNumPagesX, PRInt32 aNumPagesY);
   NS_IMETHOD  ScrollByWhole(PRBool aTop);
+  NS_IMETHOD  CanScroll(PRBool aHorizontal, PRBool aForward, PRBool &aResult);
 
   NS_IMETHOD_(nsIView*) View();