Optimize Close/MoveTo when colinear for stroking, see #74

path_intersection.go

@@ -1,6 +1,8 @@
 package canvas
 
-import "math"
+import (
+	"math"
+)
 
 // intersection between two line segments
 // see http://www.cs.swan.ac.uk/~cssimon/line_intersection.html

path_stroke.go

@@ -458,6 +458,8 @@ func offsetSegment(p *Path, halfWidth float64, cr Capper, jr Joiner) (*Path, *Pa
 	if closed {
 		rhs.Close()
 		lhs.Close()
+		optimizeMoveTo(rhs)
+		optimizeMoveTo(lhs)
 		return rhs, lhs
 	}
 
@@ -467,6 +469,7 @@ func offsetSegment(p *Path, halfWidth float64, cr Capper, jr Joiner) (*Path, *Pa
 	rhs = rhs.Join(lhs)
 	cr.Cap(rhs, halfWidth, states[0].p0, states[0].n0.Neg())
 	rhs.Close()
+	optimizeMoveTo(rhs)
 	return rhs, nil
 }
 
@@ -511,6 +514,22 @@ func closeInnerBends(p *Path, indices []int, closed bool) {
 	}
 }
 
+func optimizeMoveTo(p *Path) {
+	// move MoveTo to the initial position of the Close if they are colinear
+	if p.d[cmdLen(MoveToCmd)] == LineToCmd {
+		start := Point{p.d[len(p.d)-cmdLen(CloseCmd)-3], p.d[len(p.d)-cmdLen(CloseCmd)-2]}
+		mid := Point{p.d[1], p.d[2]}
+		end := Point{p.d[cmdLen(MoveToCmd)+1], p.d[cmdLen(MoveToCmd)+2]}
+		if Equal(end.Sub(mid).AngleBetween(mid.Sub(start)), 0.0) {
+			p.d[1] = p.d[len(p.d)-cmdLen(CloseCmd)-3]
+			p.d[2] = p.d[len(p.d)-cmdLen(CloseCmd)-2]
+			p.d[len(p.d)-cmdLen(CloseCmd)-4] = CloseCmd
+			p.d[len(p.d)-cmdLen(CloseCmd)-1] = CloseCmd
+			p.d = p.d[:len(p.d)-cmdLen(CloseCmd)]
+		}
+	}
+}
+
 // Offset offsets the path to expand by w and returns a new path. If w is negative it will contract. Path must be closed.
 func (p *Path) Offset(w float64, fillRule FillRule) *Path {
 	if Equal(w, 0.0) {