Fixed a round off error bug #29949

-r pinkerton

layout/xul/base/src/nsSliderFrame.cpp

@@ -58,6 +58,7 @@
 #include "nsIScrollableView.h"
 #include "nsRepeatService.h"
 #include "nsBoxLayoutState.h"
+#include "nsSprocketLayout.h"
 
 #define DEBUG_SLIDER PR_FALSE
 
@@ -293,25 +294,6 @@ nsSliderFrame::Layout(nsBoxLayoutState& aState)
   aState.GetPresContext()->GetScaledPixelsToTwips(&p2t);
   nscoord onePixel = NSIntPixelsToTwips(1, p2t);
 
-  /*
-  if (aReflowState.mComputedHeight == NS_INTRINSICSIZE) 
-    aDesiredSize.height = isHorizontal ? thumbSize.height : 200*onePixel;
-  else {
-    aDesiredSize.height = aReflowState.mComputedHeight;
-   // if (aDesiredSize.height < thumbSize.height)
-   //   aDesiredSize.height = thumbSize.height;
-  }
-
-  // set the width to the computed or if intrinsic then the width of the thumb.
-  if (aReflowState.mComputedWidth == NS_INTRINSICSIZE) 
-    aDesiredSize.width = isHorizontal ? 200*onePixel : thumbSize.width;
-  else {
-    aDesiredSize.width = aReflowState.mComputedWidth;
-   // if (aDesiredSize.width < thumbSize.width)
-   //   aDesiredSize.width = thumbSize.width;
-  }
-  */
-
   // get max pos in twips
   nscoord maxpos = maxpospx*onePixel;
 
@@ -327,7 +309,7 @@ nsSliderFrame::Layout(nsBoxLayoutState& aState)
   // if there is more room than the thumb need stretch the
   // thumb
 
-  nscoord thumbsize = nscoord(ourmaxpos * mRatio);
+  nscoord thumbsize = nsSprocketLayout::Round(nscoord(ourmaxpos * mRatio), onePixel);
 
   if (thumbsize > thumbcoord) {
     nscoord flex = 0;
@@ -336,9 +318,9 @@ nsSliderFrame::Layout(nsBoxLayoutState& aState)
     // if the thumb is flexible make the thumb bigger.
     if (flex > 0) {
        if (isHorizontal)
-          thumbSize.width = nscoord(ourmaxpos * mRatio);
+         thumbSize.width = thumbsize;
        else
-          thumbSize.height = nscoord(ourmaxpos * mRatio);
+          thumbSize.height = thumbsize;
     }    
   } else {
     ourmaxpos -= thumbcoord;

layout/xul/base/src/nsSprocketLayout.cpp

@@ -944,6 +944,16 @@ nsSprocketLayout::InvalidateComputedSizes(nsComputedBoxSize* aComputedBoxSizes)
   }
 }
 
+PRInt32 
+nsSprocketLayout::Round(PRInt32 aCoord, PRInt32 aOnePixel)
+{
+  PRInt32 newCoordPx = aCoord/aOnePixel;
+  PRInt32 diff = aCoord - (newCoordPx*aOnePixel);
+  if (diff > aOnePixel/2)
+     newCoordPx++;
+
+  return newCoordPx*aOnePixel;
+}
 
 void
 nsSprocketLayout::ComputeChildSizes(nsIBox* aBox,
@@ -952,6 +962,11 @@ nsSprocketLayout::ComputeChildSizes(nsIBox* aBox,
                            nsBoxSize* aBoxSizes, 
                            nsComputedBoxSize*& aComputedBoxSizes)
 {  
+
+  float p2t;
+  aState.GetPresContext()->GetScaledPixelsToTwips(&p2t);
+  nscoord onePixel = NSIntPixelsToTwips(1, p2t);
+
   PRInt32 sizeRemaining            = aGivenSize;
   PRInt32 springConstantsRemaining = 0;
 
@@ -1035,7 +1050,8 @@ nsSprocketLayout::ComputeChildSizes(nsIBox* aBox,
 
           // ----- look at our min and max limits make sure we aren't too small or too big -----
           if (!computedBoxSizes->valid) {
-            PRInt32 newSize = pref + (sizeRemaining*flex/springConstantsRemaining);
+            PRInt32 newSize = Round(pref + (sizeRemaining*flex/springConstantsRemaining), onePixel);
+
             if (newSize<=min) {
               computedBoxSizes->size = min;
               computedBoxSizes->valid = PR_TRUE;
@@ -1076,7 +1092,7 @@ nsSprocketLayout::ComputeChildSizes(nsIBox* aBox,
       flex = boxSizes->flex;
 
       if (!computedBoxSizes->valid) {
-        computedBoxSizes->size = pref + flex*sizeRemaining/springConstantsRemaining;
+        computedBoxSizes->size = Round(pref + flex*sizeRemaining/springConstantsRemaining,onePixel);
         computedBoxSizes->valid = PR_TRUE;
       }
 

layout/xul/base/src/nsSprocketLayout.h

@@ -107,6 +107,8 @@ public:
 
   nsSprocketLayout();
 
+  static PRInt32 Round(PRInt32 aCoord, PRInt32 aOnePixel);
+
 protected:
 
   virtual PRBool IsHorizontal(nsIBox* aBox) const;
@@ -156,6 +158,9 @@ protected:
   virtual void GetFrameState(nsIBox* aBox, nsFrameState& aState);
   virtual void SetFrameState(nsIBox* aBox, nsFrameState aState);
 
+private:
+
+
   // because the sprocket layout manager has no instance variables. We 
   // can make a static on and reuse it everywhere.
   static nsCOMPtr<nsIBoxLayout> gInstance;