Fixed up the dotted pattern

artist/checkered.go

@@ -0,0 +1,33 @@
+package artist
+
+import "image/color"
+
+// Checkered is a pattern that produces a grid of two alternating colors.
+type Checkered struct {
+	First  Pattern
+	Second Pattern
+	CellWidth, CellHeight int
+}
+
+// AtWhen satisfies the Pattern interface.
+func (pattern Checkered) AtWhen (x, y, width, height int) (c color.RGBA) {
+	twidth  := pattern.CellWidth  * 2
+	theight := pattern.CellHeight * 2
+	x %= twidth
+	y %= theight
+	if x < 0 { x += twidth  }
+	if y < 0 { x += theight }
+
+	n := 0
+	if x >= pattern.CellWidth  { n ++ }
+	if y >= pattern.CellHeight { n ++ }
+	
+	x %= pattern.CellWidth
+	y %= pattern.CellHeight
+
+	if n % 2 == 0 {
+		return pattern.First.AtWhen(x, y, pattern.CellWidth, pattern.CellHeight)
+	} else {
+		return pattern.Second.AtWhen(x, y, pattern.CellWidth, pattern.CellHeight)
+	}
+}

artist/dotted.go

@@ -0,0 +1,30 @@
+package artist
+
+import "math"
+import "image/color"
+
+// Dotted is a pattern that produces a grid of circles.
+type Dotted struct {
+	Background Pattern
+	Foreground Pattern
+	Size int
+	Spacing int
+}
+
+// AtWhen satisfies the Pattern interface.
+func (pattern Dotted) AtWhen (x, y, width, height int) (c color.RGBA) {
+	xm := x % pattern.Spacing
+	ym := y % pattern.Spacing
+	if xm < 0 { xm += pattern.Spacing }
+	if ym < 0 { xm += pattern.Spacing }
+	radius  := float64(pattern.Size) / 2
+	spacing := float64(pattern.Spacing) / 2 - 0.5
+	xf := float64(xm) - spacing
+	yf := float64(ym) - spacing
+
+	if math.Sqrt(xf * xf + yf * yf) > radius {
+		return pattern.Background.AtWhen(x, y, width, height)
+	} else {
+		return pattern.Foreground.AtWhen(x, y, width, height)
+	}
+}

elements/testing/artist.go

@@ -139,6 +139,42 @@ func (element *Artist) Resize (width, height int) {
 			artist.NewUniform(hex(0xFF00FFFF)),
 		},
 		element.cellAt(0, 5))
+		
+	// 1, 5
+	artist.FillRectangle (
+		element,
+		artist.Checkered {
+			First: artist.QuadBeveled {
+				artist.NewUniform(hex(0x880000FF)),
+				artist.NewUniform(hex(0x00FF00FF)),
+				artist.NewUniform(hex(0x0000FFFF)),
+				artist.NewUniform(hex(0xFF00FFFF)),
+			},
+			Second: artist.Striped {
+				First:  artist.Stroke { Pattern: uhex(0xFF8800FF), Weight: 1 },
+				Second: artist.Stroke { Pattern: uhex(0x0088FFFF), Weight: 1 },
+				Orientation: artist.OrientationVertical,
+			},
+			CellWidth: 32,
+			CellHeight: 16,
+		},
+		element.cellAt(1, 5))
+	
+	// 2, 5
+	artist.FillRectangle (
+		element,
+		artist.Dotted {
+			Foreground: uhex(0x00FF00FF),
+			Background: artist.Checkered {
+				First:  uhex(0x444444FF),
+				Second: uhex(0x888888FF),
+				CellWidth: 16,
+				CellHeight: 16,
+			},
+			Size: 8,
+			Spacing: 16,
+		},
+		element.cellAt(2, 5))
 }
 
 func (element *Artist) lines (weight int, bounds image.Rectangle) {