Polygon boundary detection now rounds properly

x/canvas/draw.go

@@ -1,6 +1,7 @@
 package xcanvas
 
 import "sort"
+import "math"
 import "image"
 import "github.com/jezek/xgbutil/xgraphics"
 
@@ -181,11 +182,11 @@ func (this *pen) fillPolygon (c xgraphics.BGRA, points ...image.Point) {
 				(fPointY < fy && fPrevY  >= fy) ||
 				(fPrevY  < fy && fPointY >= fy)
 			if addboundary {
-				context.boundaries[boundaryCount] = int (
+				context.boundaries[boundaryCount] = int(math.Round (
 					fPointX +
 					(fy - fPointY) /
 					(fPrevY - fPointY) *
-					(fPrevX - fPointX))
+					(fPrevX - fPointX)))
 				boundaryCount ++
 			}
 			prevPoint = point