Support stroke view transformation for raster, PDF, and SVG, see #74

renderers/pdf/pdf.go

@@ -84,9 +84,7 @@ func (r *PDF) Size() (float64, float64) {
 
 // RenderPath renders a path to the canvas using a style and a transformation matrix.
 func (r *PDF) RenderPath(path *canvas.Path, style canvas.Style, m canvas.Matrix) {
-	fill := style.HasFill()
-	stroke := style.HasStroke()
-	differentAlpha := fill && stroke && style.FillColor.A != style.StrokeColor.A
+	differentAlpha := style.HasFill() && style.HasStroke() && style.FillColor.A != style.StrokeColor.A
 
 	// PDFs don't support the arcs joiner, miter joiner (not clipped), or miter joiner (clipped) with non-bevel fallback
 	strokeUnsupported := false
@@ -99,6 +97,20 @@ func (r *PDF) RenderPath(path *canvas.Path, style canvas.Style, m canvas.Matrix)
 			strokeUnsupported = true
 		}
 	}
+	if !strokeUnsupported {
+		if m.IsSimilarity() {
+			scale := math.Sqrt(m.Det())
+			style.StrokeWidth *= scale
+			style.DashOffset *= scale
+			dashes := make([]float64, len(style.Dashes))
+			for i := range style.Dashes {
+				dashes[i] = style.Dashes[i] * scale
+			}
+			style.Dashes = dashes
+		} else {
+			strokeUnsupported = true
+		}
+	}
 
 	// PDFs don't support connecting first and last dashes if path is closed, so we move the start of the path if this is the case
 	// TODO: closing dashes
@@ -113,16 +125,16 @@ func (r *PDF) RenderPath(path *canvas.Path, style canvas.Style, m canvas.Matrix)
 		closed = true
 	}
 
-	if !stroke || !strokeUnsupported {
-		if fill && !stroke {
+	if !style.HasStroke() || !strokeUnsupported {
+		if style.HasFill() && !style.HasStroke() {
 			r.w.SetFillColor(style.FillColor)
 			r.w.Write([]byte(" "))
 			r.w.Write([]byte(data))
 			r.w.Write([]byte(" f"))
 			if style.FillRule == canvas.EvenOdd {
 				r.w.Write([]byte("*"))
 			}
-		} else if !fill && stroke {
+		} else if !style.HasFill() && style.HasStroke() {
 			r.w.SetStrokeColor(style.StrokeColor)
 			r.w.SetLineWidth(style.StrokeWidth)
 			r.w.SetLineCap(style.StrokeCapper)
@@ -138,7 +150,7 @@ func (r *PDF) RenderPath(path *canvas.Path, style canvas.Style, m canvas.Matrix)
 			if style.FillRule == canvas.EvenOdd {
 				r.w.Write([]byte("*"))
 			}
-		} else if fill && stroke {
+		} else if style.HasFill() && style.HasStroke() {
 			if !differentAlpha {
 				r.w.SetFillColor(style.FillColor)
 				r.w.SetStrokeColor(style.StrokeColor)
@@ -183,8 +195,8 @@ func (r *PDF) RenderPath(path *canvas.Path, style canvas.Style, m canvas.Matrix)
 			}
 		}
 	} else {
-		// stroke && strokeUnsupported
-		if fill {
+		// style.HasStroke() && strokeUnsupported
+		if style.HasFill() {
 			r.w.SetFillColor(style.FillColor)
 			r.w.Write([]byte(" "))
 			r.w.Write([]byte(data))
@@ -199,6 +211,7 @@ func (r *PDF) RenderPath(path *canvas.Path, style canvas.Style, m canvas.Matrix)
 			path = path.Dash(style.DashOffset, style.Dashes...)
 		}
 		path = path.Stroke(style.StrokeWidth, style.StrokeCapper, style.StrokeJoiner)
+		path = path.Transform(m)
 
 		r.w.SetFillColor(style.StrokeColor)
 		r.w.Write([]byte(" "))

renderers/rasterizer/rasterizer.go

@@ -81,21 +81,31 @@ func (r *Rasterizer) Size() (float64, float64) {
 // RenderPath renders a path to the canvas using a style and a transformation matrix.
 func (r *Rasterizer) RenderPath(path *canvas.Path, style canvas.Style, m canvas.Matrix) {
 	// TODO: use fill rule (EvenOdd, NonZero) for rasterizer
-	path = path.Transform(m)
-
-	strokeWidth := 0.0
+	fill := path
+	stroke := path
+	bounds := canvas.Rect{}
+	if style.HasFill() {
+		fill = path.Transform(m)
+		if !style.HasStroke() {
+			bounds = fill.Bounds()
+		}
+	}
 	if style.HasStroke() {
-		strokeWidth = style.StrokeWidth
+		if 0 < len(style.Dashes) {
+			stroke = stroke.Dash(style.DashOffset, style.Dashes...)
+		}
+		stroke = stroke.Stroke(style.StrokeWidth, style.StrokeCapper, style.StrokeJoiner)
+		stroke = stroke.Transform(m)
+		bounds = stroke.Bounds()
 	}
 
 	size := r.img.Bounds().Size()
-	bounds := path.Bounds()
 	dx, dy := 0, 0
 	dpmm := r.resolution.DPMM()
-	x := int((bounds.X - strokeWidth) * dpmm)
-	y := int((bounds.Y - strokeWidth) * dpmm)
-	w := int((bounds.W+2*strokeWidth)*dpmm) + 1
-	h := int((bounds.H+2*strokeWidth)*dpmm) + 1
+	x := int(bounds.X * dpmm)
+	y := int(bounds.Y * dpmm)
+	w := int(bounds.W*dpmm) + 1
+	h := int(bounds.H*dpmm) + 1
 	if (x+w <= 0 || size.X <= x) && (y+h <= 0 || size.Y <= y) {
 		return // outside canvas
 	}
@@ -118,20 +128,16 @@ func (r *Rasterizer) RenderPath(path *canvas.Path, style canvas.Style, m canvas.
 		return // has no size
 	}
 
-	path = path.Translate(-float64(x)/dpmm, -float64(y)/dpmm)
 	if style.HasFill() {
 		ras := vector.NewRasterizer(w, h)
-		path.ToRasterizer(ras, r.resolution)
+		fill = fill.Translate(-float64(x)/dpmm, -float64(y)/dpmm)
+		fill.ToRasterizer(ras, r.resolution)
 		ras.Draw(r.img, image.Rect(x, size.Y-y, x+w, size.Y-y-h), image.NewUniform(style.FillColor), image.Point{dx, dy})
 	}
 	if style.HasStroke() {
-		if 0 < len(style.Dashes) {
-			path = path.Dash(style.DashOffset, style.Dashes...)
-		}
-		path = path.Stroke(style.StrokeWidth, style.StrokeCapper, style.StrokeJoiner)
-
 		ras := vector.NewRasterizer(w, h)
-		path.ToRasterizer(ras, r.resolution)
+		stroke = stroke.Translate(-float64(x)/dpmm, -float64(y)/dpmm)
+		stroke.ToRasterizer(ras, r.resolution)
 		ras.Draw(r.img, image.Rect(x, size.Y-y, x+w, size.Y-y-h), image.NewUniform(style.StrokeColor), image.Point{dx, dy})
 	}
 }

renderers/svg/svg.go

@@ -150,9 +150,7 @@ func (r *SVG) Size() (float64, float64) {
 
 // RenderPath renders a path to the canvas using a style and a transformation matrix.
 func (r *SVG) RenderPath(path *canvas.Path, style canvas.Style, m canvas.Matrix) {
-	fill := style.HasFill()
-	stroke := style.HasStroke()
-
+	stroke := path
 	path = path.Transform(canvas.Identity.ReflectYAbout(r.height / 2.0).Mul(m))
 	fmt.Fprintf(r.w, `<path d="%s`, path.ToSVG())
 
@@ -166,9 +164,23 @@ func (r *SVG) RenderPath(path *canvas.Path, style canvas.Style, m canvas.Matrix)
 			strokeUnsupported = true
 		}
 	}
+	if !strokeUnsupported {
+		if m.IsSimilarity() {
+			scale := math.Sqrt(m.Det())
+			style.StrokeWidth *= scale
+			style.DashOffset *= scale
+			dashes := make([]float64, len(style.Dashes))
+			for i := range style.Dashes {
+				dashes[i] = style.Dashes[i] * scale
+			}
+			style.Dashes = dashes
+		} else {
+			strokeUnsupported = true
+		}
+	}
 
-	if !stroke {
-		if fill {
+	if !style.HasStroke() {
+		if style.HasFill() {
 			if style.FillColor != canvas.Black {
 				fmt.Fprintf(r.w, `" fill="%v`, canvas.CSSColor(style.FillColor))
 			}
@@ -180,7 +192,7 @@ func (r *SVG) RenderPath(path *canvas.Path, style canvas.Style, m canvas.Matrix)
 		}
 	} else {
 		b := &strings.Builder{}
-		if fill {
+		if style.HasFill() {
 			if style.FillColor != canvas.Black {
 				fmt.Fprintf(b, ";fill:%v", canvas.CSSColor(style.FillColor))
 			}
@@ -190,7 +202,7 @@ func (r *SVG) RenderPath(path *canvas.Path, style canvas.Style, m canvas.Matrix)
 		} else {
 			fmt.Fprintf(b, ";fill:none")
 		}
-		if stroke && !strokeUnsupported {
+		if style.HasStroke() && !strokeUnsupported {
 			fmt.Fprintf(b, `;stroke:%v`, canvas.CSSColor(style.StrokeColor))
 			if style.StrokeWidth != 1.0 {
 				fmt.Fprintf(b, ";stroke-width:%v", dec(style.StrokeWidth))
@@ -237,13 +249,14 @@ func (r *SVG) RenderPath(path *canvas.Path, style canvas.Style, m canvas.Matrix)
 	r.writeClasses(r.w)
 	fmt.Fprintf(r.w, `"/>`)
 
-	if stroke && strokeUnsupported {
-		// stroke settings unsupported by PDF, draw stroke explicitly
+	if style.HasStroke() && strokeUnsupported {
+		// stroke settings unsupported by SVG, draw stroke explicitly
 		if style.IsDashed() {
-			path = path.Dash(style.DashOffset, style.Dashes...)
+			stroke = stroke.Dash(style.DashOffset, style.Dashes...)
 		}
-		path = path.Stroke(style.StrokeWidth, style.StrokeCapper, style.StrokeJoiner)
-		fmt.Fprintf(r.w, `<path d="%s`, path.ToSVG())
+		stroke = stroke.Stroke(style.StrokeWidth, style.StrokeCapper, style.StrokeJoiner)
+		stroke = stroke.Transform(canvas.Identity.ReflectYAbout(r.height / 2.0).Mul(m))
+		fmt.Fprintf(r.w, `<path d="%s`, stroke.ToSVG())
 		if style.StrokeColor != canvas.Black {
 			fmt.Fprintf(r.w, `" fill="%v`, canvas.CSSColor(style.StrokeColor))
 		}

renderers/tex/tex.go

@@ -64,13 +64,7 @@ func (r *TeX) getColor(col color.RGBA) string {
 	return name
 }
 
-// RenderPath renders a path to the canvas using a style and a transformation matrix.
-func (r *TeX) RenderPath(path *canvas.Path, style canvas.Style, m canvas.Matrix) {
-	if path.Empty() {
-		return
-	}
-	path = path.Transform(m)
-
+func (r *TeX) writePath(path *canvas.Path) {
 	for _, seg := range path.Segments() {
 		end := seg.End
 		switch seg.Cmd {
@@ -99,11 +93,33 @@ func (r *TeX) RenderPath(path *canvas.Path, style canvas.Style, m canvas.Matrix)
 			fmt.Fprintf(r.w, "\n\\pgfpathclose")
 		}
 	}
+}
 
-	fill := style.HasFill()
-	stroke := style.HasStroke()
+// RenderPath renders a path to the canvas using a style and a transformation matrix.
+func (r *TeX) RenderPath(path *canvas.Path, style canvas.Style, m canvas.Matrix) {
+	if path.Empty() {
+		return
+	}
 
-	if fill {
+	stroke := path
+	path = path.Transform(m)
+
+	strokeUnsupported := false
+	if m.IsSimilarity() {
+		scale := math.Sqrt(m.Det())
+		style.StrokeWidth *= scale
+		style.DashOffset *= scale
+		dashes := make([]float64, len(style.Dashes))
+		for i := range style.Dashes {
+			dashes[i] = style.Dashes[i] * scale
+		}
+		style.Dashes = dashes
+	} else {
+		strokeUnsupported = true
+	}
+	r.writePath(path)
+
+	if style.HasFill() {
 		if style.FillColor.R != r.style.FillColor.R || style.FillColor.G != r.style.FillColor.G || style.FillColor.B != r.style.FillColor.B {
 			fmt.Fprintf(r.w, "\n\\pgfsetfillcolor{%v}", r.getColor(style.FillColor))
 		}
@@ -112,7 +128,7 @@ func (r *TeX) RenderPath(path *canvas.Path, style canvas.Style, m canvas.Matrix)
 		}
 	}
 
-	if stroke {
+	if style.HasStroke() && !strokeUnsupported {
 		if style.StrokeCapper != r.style.StrokeCapper {
 			if _, ok := style.StrokeCapper.(canvas.RoundCapper); ok {
 				fmt.Fprintf(r.w, "\n\\pgfsetroundcap")
@@ -161,13 +177,31 @@ func (r *TeX) RenderPath(path *canvas.Path, style canvas.Style, m canvas.Matrix)
 			fmt.Fprintf(r.w, "\n\\pgfsetstrokeopacity{%v}", dec(float64(style.StrokeColor.A)/255.0))
 		}
 	}
-	if fill && stroke {
+	if style.HasFill() && style.HasStroke() && !strokeUnsupported {
 		fmt.Fprintf(r.w, "\n\\pgfusepath{fill,stroke}")
-	} else if fill {
+	} else if style.HasFill() {
 		fmt.Fprintf(r.w, "\n\\pgfusepath{fill}")
-	} else if stroke {
+	} else if style.HasStroke() && !strokeUnsupported {
 		fmt.Fprintf(r.w, "\n\\pgfusepath{stroke}")
 	}
+
+	if style.HasStroke() && strokeUnsupported {
+		// stroke settings unsupported by TeX, draw stroke explicitly
+		if style.IsDashed() {
+			stroke = stroke.Dash(style.DashOffset, style.Dashes...)
+		}
+		stroke = stroke.Stroke(style.StrokeWidth, style.StrokeCapper, style.StrokeJoiner)
+		stroke = stroke.Transform(m)
+		r.writePath(stroke)
+		if style.StrokeColor.R != r.style.StrokeColor.R || style.StrokeColor.G != r.style.StrokeColor.G || style.StrokeColor.B != r.style.StrokeColor.B {
+			fmt.Fprintf(r.w, "\n\\pgfsetfillcolor{%v}", r.getColor(style.StrokeColor))
+		}
+		if style.StrokeColor.A != r.style.StrokeColor.A {
+			fmt.Fprintf(r.w, "\n\\pgfsetfillopacity{%v}", dec(float64(style.StrokeColor.A)/255.0))
+		}
+		fmt.Fprintf(r.w, "\n\\pgfusepath{fill}")
+
+	}
 	r.style = style
 }
 

util.go

@@ -454,20 +454,25 @@ func (m Matrix) Decompose() (float64, float64, float64, float64, float64, float6
 	return m[0][2], m[1][2], theta, sx, sy, phi
 }
 
-// IsTranslation is true if the matrix consists of only translational components, i.e. no rotation, scaling or skew.
+// IsTranslation is true if the matrix consists of only translational components, i.e. no rotation, scaling, or skew transformations.
 func (m Matrix) IsTranslation() bool {
 	return Equal(m[0][0], 1.0) && Equal(m[0][1], 0.0) && Equal(m[1][0], 0.0) && Equal(m[1][1], 1.0)
 }
 
-// IsRigid is true if the matrix consists of only (proper) rigid transformations, i.e. no scaling or skew.
+// IsRigid is true if the matrix is orthogonal and consists of only translation, rotation, and reflection transformations.
 func (m Matrix) IsRigid() bool {
-	if !Equal(m.Det(), 1.0) {
-		return false
-	}
-	invM := m.Inv()
-	invM[0][2] = m[0][2]
-	invM[1][2] = m[1][2]
-	return m.T().Equals(invM)
+	a := m[0][0]*m[0][0] + m[0][1]*m[0][1]
+	b := m[1][0]*m[1][0] + m[1][1]*m[1][1]
+	c := m[0][0]*m[1][0] + m[0][1]*m[1][1]
+	return Equal(a, 1.0) && Equal(b, 1.0) && Equal(c, 0.0)
+}
+
+// IsSimilarity is true if the matrix consists of only translation, rotation, reflection, and scaling transformations.
+func (m Matrix) IsSimilarity() bool {
+	a := m[0][0]*m[0][0] + m[0][1]*m[0][1]
+	b := m[1][0]*m[1][0] + m[1][1]*m[1][1]
+	c := m[0][0]*m[1][0] + m[0][1]*m[1][1]
+	return Equal(a, b) && Equal(c, 0.0)
 }
 
 // Equals returns true if both matrices are equal with a tolerance of Epsilon.

util_test.go

@@ -131,13 +131,26 @@ func TestMatrix(t *testing.T) {
 	test.Float(t, sy, 1.0)
 	test.Float(t, phi, -90.0)
 
+	test.T(t, Identity.Translate(1.0, 1.0).IsTranslation(), true)
+	test.T(t, Identity.Rotate(90.0).IsTranslation(), false)
+	test.T(t, Identity.Scale(-1.0, 1.0).IsTranslation(), false)
+	test.T(t, Identity.Scale(2.0, 2.0).IsTranslation(), false)
+	test.T(t, Identity.Scale(2.0, 1.0).IsTranslation(), false)
+	test.T(t, Identity.Shear(2.0, -1.0).IsTranslation(), false)
+
 	test.T(t, Identity.Translate(1.0, 1.0).IsRigid(), true)
 	test.T(t, Identity.Rotate(90.0).IsRigid(), true)
+	test.T(t, Identity.Scale(-1.0, 1.0).IsRigid(), true)
+	test.T(t, Identity.Scale(2.0, 2.0).IsRigid(), false)
 	test.T(t, Identity.Scale(2.0, 1.0).IsRigid(), false)
-	test.T(t, Identity.Scale(-1.0, 1.0).IsRigid(), false)
 	test.T(t, Identity.Shear(2.0, -1.0).IsRigid(), false)
-	test.T(t, Identity.Translate(1.0, 1.0).IsTranslation(), true)
-	test.T(t, Identity.Rotate(90.0).IsTranslation(), false)
+
+	test.T(t, Identity.Translate(1.0, 1.0).IsSimilarity(), true)
+	test.T(t, Identity.Rotate(90.0).IsSimilarity(), true)
+	test.T(t, Identity.Scale(-1.0, 1.0).IsSimilarity(), true)
+	test.T(t, Identity.Scale(2.0, 2.0).IsSimilarity(), true)
+	test.T(t, Identity.Scale(2.0, 1.0).IsSimilarity(), false)
+	test.T(t, Identity.Shear(2.0, -1.0).IsSimilarity(), false)
 
 	x, y := Identity.Translate(p.X, p.Y).Pos()
 	test.Float(t, x, p.X)