Implemented a multiborder pattern

artist/multiborder.go

@@ -0,0 +1,51 @@
+package artist
+
+import "image"
+import "image/color"
+
+type Border struct {
+	Weight int
+	Stroke Pattern
+	bounds image.Rectangle
+	dx, dy int
+}
+
+type MultiBorder struct {
+	borders []Border
+	lastWidth, lastHeight int
+	maxBorder int
+}
+
+func NewMultiBorder (borders ...Border) (multi *MultiBorder) {
+	return &MultiBorder { borders: borders }
+}
+
+func (multi *MultiBorder) AtWhen (x, y, width, height int) (c color.RGBA) {
+	if multi.lastWidth != width || multi.lastHeight != height {
+		multi.recalculate(width, height)
+	}
+	point := image.Point { x, y }
+	for index := multi.maxBorder; index >= 0; index -- {
+		border := multi.borders[index]
+		if point.In(border.bounds) {
+			return border.Stroke.AtWhen (
+				point.X - border.bounds.Min.X,
+				point.Y - border.bounds.Min.Y,
+				border.dx, border.dy)
+		}
+	}
+	return
+}
+
+func (multi *MultiBorder) recalculate (width, height int) {
+	bounds := image.Rect (0, 0, width, height)
+	multi.maxBorder = 0
+	for index, border := range multi.borders {
+		multi.maxBorder = index
+		multi.borders[index].bounds = bounds
+		multi.borders[index].dx = bounds.Dx()
+		multi.borders[index].dy = bounds.Dy()
+		bounds = bounds.Inset(border.Weight)
+		if bounds.Empty() { break }
+	}
+}

elements/testing/mouse.go

@@ -42,7 +42,7 @@ func (element *Mouse) Handle (event tomo.Event) {
 			artist.NewUniform(color.Black), 1,
 			element.Bounds())
 		artist.Line (
-			element.core, artist.NewUniform(color.White), 1,
+			element.core, artist.NewUniform(color.White), 3,
 			image.Pt(1, 1),
 			image.Pt(resizeEvent.Width - 2, resizeEvent.Height - 2))
 		artist.Line (