internal/stroke,gpu: move stroking of path data to package internal/strokg

Pure refactor, preparing for use in op/clip.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

gpu/compute.go

@@ -707,14 +707,13 @@ func encodePath(p *pathOp) encoder {
 	var enc encoder
 	verts := p.pathVerts
 	if p.stroke.Width > 0 && !supportsStroke(p) {
-		quads := decodeToStrokeQuads(verts)
 		ss := stroke.StrokeStyle{
 			Width: p.stroke.Width,
 			Miter: p.stroke.Miter,
 			Cap:   stroke.StrokeCap(p.stroke.Cap),
 			Join:  stroke.StrokeJoin(p.stroke.Join),
 		}
-		quads = quads.Stroke(ss, p.dashes)
+		quads := stroke.StrokePathCommands(ss, p.dashes, verts)
 		for _, quad := range quads {
 			q := quad.Quad
 			enc.quad(q.From, q.Ctrl, q.To)

gpu/gpu.go

@@ -1361,14 +1361,13 @@ func (d *drawOps) buildVerts(pathData []byte, tr f32.Affine2D, outline bool, str
 	switch {
 	case str.Width > 0:
 		// Stroke path.
-		quads := decodeToStrokeQuads(pathData)
 		ss := stroke.StrokeStyle{
 			Width: str.Width,
 			Miter: str.Miter,
 			Cap:   stroke.StrokeCap(str.Cap),
 			Join:  stroke.StrokeJoin(str.Join),
 		}
-		quads = quads.Stroke(ss, dashes)
+		quads := stroke.StrokePathCommands(ss, dashes, pathData)
 		for _, quad := range quads {
 			d.qs.contour = quad.Contour
 			quad.Quad = quad.Quad.Transform(tr)
@@ -1403,7 +1402,7 @@ func decodeToOutlineQuads(qs *quadSplitter, tr f32.Affine2D, pathData []byte) {
 			q = q.Transform(tr)
 			qs.splitAndEncode(q)
 		case scene.OpCubic:
-			for _, q := range splitCubic(scene.DecodeCubic(cmd)) {
+			for _, q := range stroke.SplitCubic(scene.DecodeCubic(cmd)) {
 				q = q.Transform(tr)
 				qs.splitAndEncode(q)
 			}
@@ -1414,47 +1413,6 @@ func decodeToOutlineQuads(qs *quadSplitter, tr f32.Affine2D, pathData []byte) {
 	}
 }
 
-// decodeToStrokeQuads is like decodeOutlineQuads, except it returns a list of stroke
-// quads ready to stroke.
-func decodeToStrokeQuads(pathData []byte) stroke.StrokeQuads {
-	quads := make(stroke.StrokeQuads, 0, 2*len(pathData)/(scene.CommandSize+4))
-	for len(pathData) >= scene.CommandSize+4 {
-		contour := bo.Uint32(pathData)
-		cmd := ops.DecodeCommand(pathData[4:])
-		switch cmd.Op() {
-		case scene.OpLine:
-			var q stroke.QuadSegment
-			q.From, q.To = scene.DecodeLine(cmd)
-			q.Ctrl = q.From.Add(q.To).Mul(.5)
-			quad := stroke.StrokeQuad{
-				Contour: contour,
-				Quad:    q,
-			}
-			quads = append(quads, quad)
-		case scene.OpQuad:
-			var q stroke.QuadSegment
-			q.From, q.Ctrl, q.To = scene.DecodeQuad(cmd)
-			quad := stroke.StrokeQuad{
-				Contour: contour,
-				Quad:    q,
-			}
-			quads = append(quads, quad)
-		case scene.OpCubic:
-			for _, q := range splitCubic(scene.DecodeCubic(cmd)) {
-				quad := stroke.StrokeQuad{
-					Contour: contour,
-					Quad:    q,
-				}
-				quads = append(quads, quad)
-			}
-		default:
-			panic("unsupported scene command")
-		}
-		pathData = pathData[scene.CommandSize+4:]
-	}
-	return quads
-}
-
 // create GPU vertices for transformed r, find the bounds and establish texture transform.
 func (d *drawOps) boundsForTransformedRect(r f32.Rectangle, tr f32.Affine2D) (aux []byte, bnd f32.Rectangle, ptr f32.Affine2D) {
 	if isPureOffset(tr) {
@@ -1534,78 +1492,3 @@ func isPureOffset(t f32.Affine2D) bool {
 	a, b, _, d, e, _ := t.Elems()
 	return a == 1 && b == 0 && d == 0 && e == 1
 }
-
-func splitCubic(from, ctrl0, ctrl1, to f32.Point) []stroke.QuadSegment {
-	quads := make([]stroke.QuadSegment, 0, 10)
-	// Set the maximum distance proportionally to the longest side
-	// of the bounding rectangle.
-	hull := f32.Rectangle{
-		Min: from,
-		Max: ctrl0,
-	}.Canon().Add(ctrl1).Add(to)
-	l := hull.Dx()
-	if h := hull.Dy(); h > l {
-		l = h
-	}
-	approxCubeTo(&quads, 0, l*0.001, from, ctrl0, ctrl1, to)
-	return quads
-}
-
-// approxCube approximates a cubic Bézier by a series of quadratic
-// curves.
-func approxCubeTo(quads *[]stroke.QuadSegment, splits int, maxDist float32, from, ctrl0, ctrl1, to f32.Point) int {
-	// The idea is from
-	// https://caffeineowl.com/graphics/2d/vectorial/cubic2quad01.html
-	// where a quadratic approximates a cubic by eliminating its t³ term
-	// from its polynomial expression anchored at the starting point:
-	//
-	// P(t) = pen + 3t(ctrl0 - pen) + 3t²(ctrl1 - 2ctrl0 + pen) + t³(to - 3ctrl1 + 3ctrl0 - pen)
-	//
-	// The control point for the new quadratic Q1 that shares starting point, pen, with P is
-	//
-	// C1 = (3ctrl0 - pen)/2
-	//
-	// The reverse cubic anchored at the end point has the polynomial
-	//
-	// P'(t) = to + 3t(ctrl1 - to) + 3t²(ctrl0 - 2ctrl1 + to) + t³(pen - 3ctrl0 + 3ctrl1 - to)
-	//
-	// The corresponding quadratic Q2 that shares the end point, to, with P has control
-	// point
-	//
-	// C2 = (3ctrl1 - to)/2
-	//
-	// The combined quadratic Bézier, Q, shares both start and end points with its cubic
-	// and use the midpoint between the two curves Q1 and Q2 as control point:
-	//
-	// C = (3ctrl0 - pen + 3ctrl1 - to)/4
-	c := ctrl0.Mul(3).Sub(from).Add(ctrl1.Mul(3)).Sub(to).Mul(1.0 / 4.0)
-	const maxSplits = 32
-	if splits >= maxSplits {
-		*quads = append(*quads, stroke.QuadSegment{From: from, Ctrl: c, To: to})
-		return splits
-	}
-	// The maximum distance between the cubic P and its approximation Q given t
-	// can be shown to be
-	//
-	// d = sqrt(3)/36*|to - 3ctrl1 + 3ctrl0 - pen|
-	//
-	// To save a square root, compare d² with the squared tolerance.
-	v := to.Sub(ctrl1.Mul(3)).Add(ctrl0.Mul(3)).Sub(from)
-	d2 := (v.X*v.X + v.Y*v.Y) * 3 / (36 * 36)
-	if d2 <= maxDist*maxDist {
-		*quads = append(*quads, stroke.QuadSegment{From: from, Ctrl: c, To: to})
-		return splits
-	}
-	// De Casteljau split the curve and approximate the halves.
-	t := float32(0.5)
-	c0 := from.Add(ctrl0.Sub(from).Mul(t))
-	c1 := ctrl0.Add(ctrl1.Sub(ctrl0).Mul(t))
-	c2 := ctrl1.Add(to.Sub(ctrl1).Mul(t))
-	c01 := c0.Add(c1.Sub(c0).Mul(t))
-	c12 := c1.Add(c2.Sub(c1).Mul(t))
-	c0112 := c01.Add(c12.Sub(c01).Mul(t))
-	splits++
-	splits = approxCubeTo(quads, splits, maxDist, from, c0, c01, c0112)
-	splits = approxCubeTo(quads, splits, maxDist, c0112, c12, c2, to)
-	return splits
-}