Move some drawing functionality into internal package

internal/draw.go

@@ -0,0 +1,27 @@
+package internal
+
+import "image"
+import "image/draw"
+import "image/color"
+import "golang.org/x/image/math/fixed"
+
+func DrawRectangleOutline (destination draw.Image, bounds image.Rectangle, col color.Color) {
+	for x := bounds.Min.X; x < bounds.Max.X; x ++ {
+		destination.Set(x, bounds.Min.Y, col)
+	}
+	for y := bounds.Min.Y; y < bounds.Max.Y; y ++ {
+		destination.Set(bounds.Min.X, y, col)
+		destination.Set(bounds.Max.X - 1, y, col)
+	}
+	for x := bounds.Min.X; x < bounds.Max.X; x ++ {
+		destination.Set(x, bounds.Max.Y - 1, col)
+	}
+}
+
+func RoundRect (rectangle fixed.Rectangle26_6) image.Rectangle {
+	return image.Rect (
+		rectangle.Min.X.Round(),
+		rectangle.Min.Y.Round(),
+		rectangle.Max.X.Round(),
+		rectangle.Max.Y.Round())
+}