gpu,op/clip: implement stroked paths with miter joins

Signed-off-by: Sebastien Binet <s@sbinet.org>

op/clip/clip.go

@@ -55,6 +55,7 @@ func (p Op) Add(o *op.Ops) {
 	bo.PutUint32(data[17:], math.Float32bits(p.width))
 	data[21] = uint8(p.style.Cap)
 	data[22] = uint8(p.style.Join)
+	bo.PutUint32(data[23:], math.Float32bits(p.style.Miter))
 }
 
 // Begin the path, storing the path data and final Op into ops.

op/clip/stroke.go

@@ -8,6 +8,11 @@ package clip
 type StrokeStyle struct {
 	Cap  StrokeCap
 	Join StrokeJoin
+
+	// Miter is the limit to apply to a miter joint.
+	// The zero Miter disables the miter joint; setting Miter to +∞
+	// unconditionally enables the miter joint.
+	Miter float32
 }
 
 // StrokeCap describes the head or tail of a stroked path.