Add command-line option -hollowcircles; controls drawing of 'o'

If set, the letter 'o' draws a hollow circle, with strokes possibly
extending into it; otherwise, the circle is filled with a computed
inverse of the foreground drawing color.

Author: dmullis

cmd/goat/main.go

@@ -36,6 +36,10 @@ func main() {
 
  See https://developer.mozilla.org/en-US/docs/Web/CSS/@media/prefers-color-scheme
 `)
+	flag.BoolVar(&goat.HollowCircles, "hollowcircles", false,
+		`If set, the letter 'o' draws a hollow circle, with strokes possibly extending
+into it; otherwise, the circle is filled with a computed inverse of the foreground
+drawing color.`)
 	flag.Parse()
 
 	format = strings.ToLower(format)

svg.go

@@ -6,6 +6,8 @@ import (
 	"io"
 )
 
+var HollowCircles bool
+
 type SVG struct {
 	Body   string
 	Width  int
@@ -260,12 +262,15 @@ func (t Triangle) Draw(out io.Writer) {
 
 // Draw a solid circle as an SVG circle element.
 func (c *Circle) Draw(out io.Writer) {
-	fill := "none"
-
+	var fill string
 	if c.bold {
 		fill = "currentColor"
+	} else {
+		fill = "invert(currentColor)"
+		if HollowCircles {
+			fill = "none"
+		}
 	}
-
 	pixel := c.start.asPixel()
 
 	writeBytes(out,