implemented line dash offset

README.md

@@ -111,6 +111,7 @@ These features *should* work just like their HTML5 counterparts, but there are l
 - miterLimit
 - lineDash
 - getLineDash
+- lineDashOffset
 - global alpha
 - drawImage
 - getImageData
@@ -123,7 +124,6 @@ These features *should* work just like their HTML5 counterparts, but there are l
 # Missing features
 
 - globalCompositeOperation
-- lineDashOffset
 - textBaseline
 - isPointInPath
 - isPointInStroke

canvas.go

@@ -684,6 +684,10 @@ func (cv *Canvas) SetLineDash(dash []float64) {
 	cv.state.lineDashOffset = 0
 }
 
+func (cv *Canvas) SetLineDashOffset(offset float64) {
+	cv.state.lineDashOffset = offset
+}
+
 // GetLineDash gets the line dash style
 func (cv *Canvas) GetLineDash() []float64 {
 	result := make([]float64, len(cv.state.lineDash))

canvas_test.go

@@ -239,6 +239,35 @@ func TestLineDash(t *testing.T) {
 	})
 }
 
+func TestLineDashOffset(t *testing.T) {
+	run(t, func(cv *canvas.Canvas) {
+		cv.SetStrokeStyle("#0F0")
+		cv.SetLineWidth(2.5)
+		cv.SetLineDash([]float64{4, 6, 8})
+		cv.SetLineDashOffset(5)
+		cv.BeginPath()
+		cv.MoveTo(20, 20)
+		cv.LineTo(80, 20)
+		cv.LineTo(80, 80)
+		cv.LineTo(50, 80)
+		cv.LineTo(50, 50)
+		cv.LineTo(20, 50)
+		cv.ClosePath()
+		cv.MoveTo(30, 30)
+		cv.LineTo(70, 30)
+		cv.LineTo(70, 70)
+		cv.LineTo(60, 70)
+		cv.LineTo(60, 40)
+		cv.LineTo(30, 40)
+		cv.ClosePath()
+		cv.Stroke()
+		ld := cv.GetLineDash()
+		if ld[0] != 4 || ld[1] != 6 || ld[2] != 8 || ld[3] != 4 || ld[4] != 6 || ld[5] != 8 {
+			t.Fail()
+		}
+	})
+}
+
 func TestCurves(t *testing.T) {
 	run(t, func(cv *canvas.Canvas) {
 		cv.SetStrokeStyle("#00F")