added support for miter limit

README.md

@@ -115,12 +115,12 @@ These features *should* work just like their HTML5 counterparts, but there are l
 - clearRect
 - shadowColor
 - shadowOffset(X/Y)
+- miterLimit
 
 # Missing features
 
 - globalCompositeOperation
 - lineDashOffset
-- miterLimit
 - shadowBlur
 - textBaseline
 - getLineDash

canvas.go

@@ -27,17 +27,18 @@ type Canvas struct {
 }
 
 type drawState struct {
-	transform   mat
+	transform     mat
-	fill        drawStyle
+	fill          drawStyle
-	stroke      drawStyle
+	stroke        drawStyle
-	font        *Font
+	font          *Font
-	fontSize    float64
+	fontSize      float64
-	textAlign   textAlign
+	textAlign     textAlign
-	lineAlpha   float64
+	lineAlpha     float64
-	lineWidth   float64
+	lineWidth     float64
-	lineJoin    lineJoin
+	lineJoin      lineJoin
-	lineEnd     lineEnd
+	lineEnd       lineEnd
-	globalAlpha float64
+	miterLimitSqr float64
+	globalAlpha   float64
 
 	lineDash       []float64
 	lineDashPoint  int
@@ -105,6 +106,7 @@ func New(x, y, w, h int) *Canvas {
 	cv.SetBounds(x, y, w, h)
 	cv.state.lineWidth = 1
 	cv.state.lineAlpha = 1
+	cv.state.miterLimitSqr = 100
 	cv.state.globalAlpha = 1
 	cv.state.fill.color = glColor{a: 1}
 	cv.state.stroke.color = glColor{a: 1}
@@ -583,6 +585,12 @@ func (cv *Canvas) SetLineDash(dash []float64) {
 	cv.state.lineDashOffset = 0
 }
 
+// SetMiterLimit sets the limit for how far a miter line join can be extend.
+// The fallback is a bevel join
+func (cv *Canvas) SetMiterLimit(limit float64) {
+	cv.state.miterLimitSqr = limit * limit
+}
+
 // SetGlobalAlpha sets the global alpha value
 func (cv *Canvas) SetGlobalAlpha(alpha float64) {
 	cv.state.globalAlpha = alpha

paths.go

@@ -431,6 +431,17 @@ func (cv *Canvas) lineJoint(p pathPoint, p0, p1, p2, l0p0, l0p1, l0p2, l0p3 vec,
 				ip0 = l0p1.add(l1p1).mulf(0.5)
 			}
 		}
+
+		if dist := ip0.sub(l0p1).lenSqr(); dist > cv.state.miterLimitSqr {
+			l1p1 := p1.sub(v3)
+			l1p3 := p1.add(v3)
+
+			tris = append(tris,
+				float32(p1[0]), float32(p1[1]), float32(l0p1[0]), float32(l0p1[1]), float32(l1p1[0]), float32(l1p1[1]),
+				float32(p1[0]), float32(p1[1]), float32(l1p3[0]), float32(l1p3[1]), float32(l0p3[0]), float32(l0p3[1]))
+			return tris
+		}
+
 		if l0p3.sub(l1p3).lenSqr() < 0.000000001 {
 			ip1 = l0p3.sub(l1p3).mulf(0.5).add(l1p3)
 		} else {
@@ -441,6 +452,16 @@ func (cv *Canvas) lineJoint(p pathPoint, p0, p1, p2, l0p0, l0p1, l0p2, l0p3 vec,
 			}
 		}
 
+		if dist := ip1.sub(l1p1).lenSqr(); dist > cv.state.miterLimitSqr {
+			l1p1 := p1.sub(v3)
+			l1p3 := p1.add(v3)
+
+			tris = append(tris,
+				float32(p1[0]), float32(p1[1]), float32(l0p1[0]), float32(l0p1[1]), float32(l1p1[0]), float32(l1p1[1]),
+				float32(p1[0]), float32(p1[1]), float32(l1p3[0]), float32(l1p3[1]), float32(l0p3[0]), float32(l0p3[1]))
+			return tris
+		}
+
 		tris = append(tris,
 			float32(p1[0]), float32(p1[1]), float32(l0p1[0]), float32(l0p1[1]), float32(ip0[0]), float32(ip0[1]),
 			float32(p1[0]), float32(p1[1]), float32(ip0[0]), float32(ip0[1]), float32(l1p1[0]), float32(l1p1[1]),