random circles example

circle.go

@@ -0,0 +1,24 @@
+package imageutils
+
+import (
+	"image"
+	"image/color"
+)
+
+// go.dev/blog/image-draw#drawing-through-a-mask
+type Circle struct {
+	image.Point
+	R int
+}
+
+func (c Circle) ColorModel() color.Model { return color.AlphaModel }
+func (c Circle) Bounds() image.Rectangle {
+	return image.Rect(c.Point.X-c.R, c.Point.Y-c.R, c.Point.X+c.R, c.Point.Y+c.R)
+}
+func (c Circle) At(x, y int) color.Color {
+	xx, yy, rr := float64(x-c.Point.X)+0.5, float64(y-c.Point.Y)+0.5, float64(c.R)
+	if xx*xx+yy*yy < rr*rr {
+		return color.Opaque
+	}
+	return color.Transparent
+}