fixed Arc and ArcTo scaling

canvas.go

@@ -141,7 +141,7 @@ func New(backend backendbase.Backend) *Canvas {
 	cv.state.globalAlpha = 1
 	cv.state.fill.color = color.RGBA{A: 255}
 	cv.state.stroke.color = color.RGBA{A: 255}
-	cv.state.transform = matIdentity()
+	cv.state.transform = matIdentity
 	cv.path.cv = cv
 	return cv
 }
@@ -395,7 +395,7 @@ func (cv *Canvas) Restore() {
 	cv.b.ClearClip()
 	for _, st := range cv.stateStack {
 		if len(st.clip.p) > 0 {
-			cv.clip(&st.clip, matIdentity())
+			cv.clip(&st.clip, matIdentity)
 		}
 	}
 	cv.state = cv.stateStack[l-1]

math.go

@@ -79,12 +79,10 @@ func (m *mat) String() string {
 	return fmt.Sprintf("[%f,%f,0,\n %f,%f,0,\n %f,%f,1,]", m[0], m[2], m[4], m[1], m[3], m[5])
 }
 
-func matIdentity() mat {
-	return mat{
+var matIdentity = mat{
 	1, 0,
 	0, 1,
 	0, 0}
-}
 
 func matTranslate(v vec) mat {
 	return mat{

path2d.go

@@ -114,13 +114,21 @@ func (p *Path2D) lineTo(x, y float64, checkSelfIntersection bool) {
 
 // Arc (see equivalent function on canvas type)
 func (p *Path2D) Arc(x, y, radius, startAngle, endAngle float64, anticlockwise bool) {
+	p.arc(x, y, radius, startAngle, endAngle, anticlockwise, matIdentity, true)
+}
+
+func (p *Path2D) arc(x, y, radius, startAngle, endAngle float64, anticlockwise bool, m mat, ident bool) {
 	checkSelfIntersection := len(p.p) > 0
 
 	lastWasMove := len(p.p) == 0 || p.p[len(p.p)-1].flags&pathMove != 0
 
 	if endAngle == startAngle {
 		s, c := math.Sincos(endAngle)
-		p.lineTo(x+radius*c, y+radius*s, checkSelfIntersection)
+		pt := vec{x + radius*c, y + radius*s}
+		if !ident {
+			pt = pt.mulMat(m)
+		}
+		p.lineTo(pt[0], pt[1], checkSelfIntersection)
 
 		if lastWasMove {
 			p.p[len(p.p)-1].flags |= pathIsConvex
@@ -153,16 +161,28 @@ func (p *Path2D) Arc(x, y, radius, startAngle, endAngle float64, anticlockwise b
 	if !anticlockwise {
 		for a := startAngle; a < endAngle; a += step {
 			s, c := math.Sincos(a)
-			p.lineTo(x+radius*c, y+radius*s, checkSelfIntersection)
+			pt := vec{x + radius*c, y + radius*s}
+			if !ident {
+				pt = pt.mulMat(m)
+			}
+			p.lineTo(pt[0], pt[1], checkSelfIntersection)
 		}
 	} else {
 		for a := startAngle; a > endAngle; a -= step {
 			s, c := math.Sincos(a)
-			p.lineTo(x+radius*c, y+radius*s, checkSelfIntersection)
+			pt := vec{x + radius*c, y + radius*s}
+			if !ident {
+				pt = pt.mulMat(m)
+			}
+			p.lineTo(pt[0], pt[1], checkSelfIntersection)
 		}
 	}
 	s, c := math.Sincos(endAngle)
-	p.lineTo(x+radius*c, y+radius*s, checkSelfIntersection)
+	pt := vec{x + radius*c, y + radius*s}
+	if !ident {
+		pt = pt.mulMat(m)
+	}
+	p.lineTo(pt[0], pt[1], checkSelfIntersection)
 
 	if lastWasMove {
 		p.p[len(p.p)-1].flags |= pathIsConvex
@@ -171,10 +191,17 @@ func (p *Path2D) Arc(x, y, radius, startAngle, endAngle float64, anticlockwise b
 
 // ArcTo (see equivalent function on canvas type)
 func (p *Path2D) ArcTo(x1, y1, x2, y2, radius float64) {
+	p.arcTo(x1, y1, x2, y2, radius, matIdentity, true)
+}
+
+func (p *Path2D) arcTo(x1, y1, x2, y2, radius float64, m mat, ident bool) {
 	if len(p.p) == 0 {
 		return
 	}
 	p0, p1, p2 := p.p[len(p.p)-1].pos, vec{x1, y1}, vec{x2, y2}
+	if !ident {
+		p0 = p0.mulMat(m.invert())
+	}
 	v0, v1 := p0.sub(p1).norm(), p2.sub(p1).norm()
 	angle := math.Acos(v0.dot(v1))
 	// should be in the range [0-pi]. if parallel, use a straight line
@@ -201,7 +228,7 @@ func (p *Path2D) ArcTo(x1, y1, x2, y2, radius float64) {
 			a1 += math.Pi * 2
 		}
 	}
-	p.Arc(center[0], center[1], radius, a0, a1, x > 0)
+	p.arc(center[0], center[1], radius, a0, a1, x > 0, m, ident)
 }
 
 // QuadraticCurveTo (see equivalent function on canvas type)

paths.go

@@ -32,11 +32,10 @@ func (cv *Canvas) LineTo(x, y float64) {
 // is the radius, startAngle and endAngle are angles in radians, anticlockwise
 // means that the line is added anticlockwise
 func (cv *Canvas) Arc(x, y, radius, startAngle, endAngle float64, anticlockwise bool) {
-	tf := cv.tf(vec{x, y})
 	ax, ay := math.Sincos(startAngle)
 	startAngle2 := vec{ay, ax}.mulMat2(cv.state.transform.mat2()).atan2()
 	endAngle2 := startAngle2 + (endAngle - startAngle)
-	cv.path.Arc(tf[0], tf[1], radius, startAngle2, endAngle2, anticlockwise)
+	cv.path.arc(x, y, radius, startAngle2, endAngle2, anticlockwise, cv.state.transform, false)
 }
 
 // ArcTo adds to the current path by drawing a line toward x1/y1 and a circle
@@ -44,9 +43,7 @@ func (cv *Canvas) Arc(x, y, radius, startAngle, endAngle float64, anticlockwise
 // lines from the end of the path to x1/y1, and from x1/y1 to x2/y2. The line
 // will only go to where the circle segment would touch the latter line
 func (cv *Canvas) ArcTo(x1, y1, x2, y2, radius float64) {
-	tf1 := cv.tf(vec{x1, y1})
-	tf2 := cv.tf(vec{x2, y2})
-	cv.path.ArcTo(tf1[0], tf1[1], tf2[0], tf2[1], radius)
+	cv.path.arcTo(x1, y1, x2, y2, radius, cv.state.transform, false)
 }
 
 // QuadraticCurveTo adds a quadratic curve to the path. It uses the current end
@@ -368,7 +365,7 @@ func linePointDistSqr(a, b, p vec) float64 {
 
 // Fill fills the current path with the current FillStyle
 func (cv *Canvas) Fill() {
-	cv.fillPath(&cv.path, matIdentity())
+	cv.fillPath(&cv.path, matIdentity)
 }
 
 // FillPath fills the given path with the current FillStyle
@@ -426,7 +423,7 @@ func appendSubPathTriangles(tris [][2]float64, mat mat, path []pathPoint) [][2]f
 // Clip uses the current path to clip any further drawing. Use Save/Restore to
 // remove the clipping again
 func (cv *Canvas) Clip() {
-	cv.clip(&cv.path, matIdentity())
+	cv.clip(&cv.path, matIdentity)
 }
 
 func (cv *Canvas) clip(path *Path2D, tf mat) {