Bug 173051. Do transforms consistently. r+sr=dbaron

gfx/src/nsTransform2D.cpp

@@ -432,14 +432,8 @@ void nsTransform2D :: TransformCoord(nscoord *ptX, nscoord *ptY)
       break;
 
     case MG_2DSCALE | MG_2DTRANSLATION:
-      // You can not use a translation that is not rounded to calculate a 
-      // final destination and get consistent results.  The translation is rounded 
-      // separately only for the final coordinate location.  Its ok 
-      // to keep the tranlation in floating for the matrix.. just don't use it
-      // pre-rounded for coordinate locations.  Its not valid to translate 1.333 pixels for example
-      // on output since .33 pixel is not a valid output unit and can cause inconsistencies. (dcone)
-      *ptX = NSToCoordRound(*ptX * m00) + NSToCoordRound(m20);
-      *ptY = NSToCoordRound(*ptY * m11) + NSToCoordRound(m21);
+      *ptX = NSToCoordRound(*ptX * m00 + m20);
+      *ptY = NSToCoordRound(*ptY * m11 + m21);
       break;
 
     default:
@@ -517,85 +511,12 @@ void nsTransform2D :: Transform(float *aX, float *aY, float *aWidth, float *aHei
 
 void nsTransform2D :: TransformCoord(nscoord *aX, nscoord *aY, nscoord *aWidth, nscoord *aHeight)
 {
-  float x, y;
-  float ex,ey;
-
-  switch (type)
-  {
-    case MG_2DIDENTITY:
-      break;
-
-    case MG_2DTRANSLATION:
-      *aX += NSToCoordRound(m20);
-      *aY += NSToCoordRound(m21);
-      break;
-
-    case MG_2DSCALE:
-      *aX = NSToCoordRound(*aX * m00);
-      *aY = NSToCoordRound(*aY * m11);
-      *aWidth = NSToCoordRound(*aWidth * m00);
-      *aHeight = NSToCoordRound(*aHeight * m11);
-      break;
-
-    case MG_2DGENERAL:
-      x = (float)*aX;
-      y = (float)*aY;
-
-      *aX = NSToCoordRound(x * m00 + y * m10);
-      *aY = NSToCoordRound(x * m01 + y * m11);
-
-      x = (float)*aWidth;
-      y = (float)*aHeight;
-
-      *aWidth = NSToCoordRound(x * m00 + y * m10);
-      *aHeight = NSToCoordRound(x * m01 + y * m11);
-
-      break;
-
-    case MG_2DSCALE | MG_2DTRANSLATION:
-      // first transform the X and Y locations
-      x = *aX * m00 + NSToCoordRound(m20);
-      y = *aY * m11 + NSToCoordRound(m21);
-      *aX =  NSToCoordRound(x);
-      *aY =  NSToCoordRound(y);
-
-      // the starting locations have a direct effect on the width and height if and only if
-      // the width and height are used to calculate positions relative to these locations.
-      // The layout engine does count on the width and height to be so many units away, so an
-      // error can be introduced if you round and then add a rounded width. To compensate, this error
-      // should be added to the width or height before rounding.  If the width or height is used as a 
-      // measurment, or distance, then use the direct floating point number.  This width and height 
-      // has an error adjustment for the starting locations inorder to calculate the ending positions.
-      // The error is the fractional difference between the transformed point and the next  pixel
-
-      // calculate the error
-      ex = x - float(NSToCoordRound(x));
-      ey = y - float(NSToCoordRound(y));
-
-      // now you can transform with the error added in
-      *aWidth = NSToCoordRound(*aWidth * m00 + ex);
-      *aHeight = NSToCoordRound(*aHeight * m11 + ey);
-      break;
-
-    default:
-    case MG_2DGENERAL | MG_2DTRANSLATION:
-      x = (float)*aX;
-      y = (float)*aY;
-      
-      x = x * m00 + y * m10 + m20;
-      y = x * m01 + y * m11 + m21;
-      ex = x - float(NSToCoordRound(x));
-      ey = y - float(NSToCoordRound(y));
-      *aX = NSToCoordRound(x);
-      *aY = NSToCoordRound(y);
-
-      x = (float)*aWidth;
-      y = (float)*aHeight;
-
-      *aWidth = NSToCoordRound((x * m00 + y * m10)+ex);
-      *aHeight = NSToCoordRound((x * m01 + y * m11)+ey);
-      break;
-  }
+  nscoord x2 = *aX + *aWidth;
+  nscoord y2 = *aY + *aHeight;
+  TransformCoord(aX, aY);
+  TransformCoord(&x2, &y2);
+  *aWidth = x2 - *aX;
+  *aHeight = y2 - *aY;
 }
 
 void nsTransform2D :: AddTranslation(float ptX, float ptY)