Refactor: internal.RuleDiamond and internal.Frame ornaments

RuleDiamond draws the rule-diamond-rule of Heading, Dialog, Result, Card
titles and the ornament Divider; Frame draws the inset line with corner
diamonds of Card and decorated Dialog. Both snap the diamonds, and the
rule's diamond sits on the pixel-aligned line.

Snapshots: card (all densities, light and dark) moves the title rule's
diamond onto the rule's pixel row, an 8x8 region. Decorated dialog
(both densities, light and dark) loses the surface-colored halo under
each corner diamond, so the frame line now runs into the diamond as on
Card and the panel border is no longer notched at the corners.
Heading, Divider and Result render unchanged.

dialog.go

@@ -91,23 +91,11 @@ func dialogPanel(c *ui.Context, panel *ui.Element, width float32, decorated bool
 	panel.Width(width).MaxWidth(w-32).MaxHeight(h-32).Padding(u*6).Gap(u*3).Margin(8*(1-p), 0, 0, 0)
 	if decorated {
 		panel.Border(theme.BorderWidth, k.Ornament).Padding(u*6 + 6).DrawOver(func(pt *ui.Painter, r ui.Rect) {
-			dialogOrnaments(pt, r, k.Ornament, k.Surface)
+			internal.Frame(pt, r, 5, 7, k.Ornament)
 		})
 	}
 }
 
-// dialogOrnaments draws the inner frame and the four corner diamonds.
-func dialogOrnaments(p *ui.Painter, r ui.Rect, ink, ground ui.Color) {
-	const in = 5
-	f := ui.Rect{X: r.X + in, Y: r.Y + in, W: r.W - 2*in, H: r.H - 2*in}
-	p.Stroke(f, ink, 1, 1)
-	for _, pt := range [4][2]float32{{f.X, f.Y}, {f.X + f.W, f.Y}, {f.X, f.Y + f.H}, {f.X + f.W, f.Y + f.H}} {
-		x, y := internal.Snap(p, pt[0]), internal.Snap(p, pt[1])
-		p.FillPath(internal.Diamond(x, y, 11), ground)
-		p.FillPath(internal.Diamond(x, y, 7), ink)
-	}
-}
-
 // dialogHeader builds the title and close button; it reports a close click.
 func dialogHeader(c *ui.Context, title string, decorated, closable bool, closeKey string) bool {
 	k := Tokens(c)
@@ -130,10 +118,7 @@ func dialogHeader(c *ui.Context, title string, decorated, closable bool, closeKe
 // dialogRule is the ornament line under a decorated title.
 func dialogRule(c *ui.Context, ink ui.Color) {
 	ui.Box(c).FillWidth().Height(9).Margin(2, 0, 2, 0).Draw(func(p *ui.Painter, r ui.Rect) {
-		y, cx := r.Y+r.H/2, r.X+r.W/2
-		p.Line(r.X, y, cx-10, y, 1, ink)
-		p.Line(cx+10, y, r.X+r.W, y, 1, ink)
-		p.FillPath(internal.Diamond(internal.Snap(p, cx), internal.Snap(p, y), 7), ink)
+		internal.RuleDiamond(p, r, 10, 7, ink)
 	})
 }