Created the split pattern

artist/split.go

@@ -0,0 +1,43 @@
+package artist
+
+import "image/color"
+
+// Orientation specifies an eight-way pattern orientation.
+type Orientation int
+
+const (
+	OrientationVertical Orientation = iota
+	OrientationDiagonalRight
+	OrientationHorizontal
+	OrientationDiagonalLeft
+)
+
+// Split is a pattern that is divided in half between two sub-patterns.
+type Split struct {
+	First  Pattern
+	Second Pattern
+	Orientation
+}
+
+// AtWhen satisfies the Pattern interface.
+func (pattern Split) AtWhen (x, y, width, height int) (c color.RGBA) {
+	var first bool
+	switch pattern.Orientation {
+	case OrientationVertical:
+		first = x < width / 2
+	case OrientationDiagonalRight:
+		first = float64(x) / float64(width) +
+			float64(y) / float64(height) < 1
+	case OrientationHorizontal:
+		first = y < height / 2
+	case OrientationDiagonalLeft:
+		first = float64(width - x) / float64(width) +
+			float64(y) / float64(height) < 1
+	}
+	
+	if first {
+		return pattern.First.AtWhen(x, y, width, height)
+	} else {
+		return pattern.Second.AtWhen(x, y, width, height)
+	}
+}

artist/striped.go

@@ -2,34 +2,24 @@ package artist
 
 import "image/color"
 
-// StripeDirection specifies the direction of stripes.
-type StripeDirection int
-
-const (
-	StripeDirectionVertical StripeDirection = iota
-	StripeDirectionDiagonalRight
-	StripeDirectionHorizontal
-	StripeDirectionDiagonalLeft
-)
-
 // Striped is a pattern that produces stripes of two alternating colors.
 type Striped struct {
 	First  Stroke
 	Second Stroke
-	Direction StripeDirection
+	Orientation
 }
 
 // AtWhen satisfies the Pattern interface.
 func (pattern Striped) AtWhen (x, y, width, height int) (c color.RGBA) {
 	position := 0
-	switch pattern.Direction {
+	switch pattern.Orientation {
-	case StripeDirectionVertical:
+	case OrientationVertical:
 		position = x
-	case StripeDirectionDiagonalRight:
+	case OrientationDiagonalRight:
 		position = x + y
-	case StripeDirectionHorizontal:
+	case OrientationHorizontal:
 		position = y
-	case StripeDirectionDiagonalLeft:
+	case OrientationDiagonalLeft:
 		position = x - y
 	}