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vector_renderer: SVG rendering performance gains by using bytes.Buffer
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Validated using benchmarks to both reduce memory pressure and be faster.
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@jentfoo
jentfoo committed Jan 20, 2025
1 parent ca9fb88 commit f91a619
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Showing 2 changed files with 87 additions and 51 deletions.
126 changes: 78 additions & 48 deletions chartdraw/vector_renderer.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -166,7 +166,7 @@ func (vr *vectorRenderer) FillStroke() {

// drawPath draws the path set into the p slice.
func (vr *vectorRenderer) drawPath() {
vr.c.Path(strings.Join(vr.p, "\n"), vr.s.GetFillAndStrokeOptions())
vr.c.Path(vr.p, vr.s.GetFillAndStrokeOptions())
vr.p = vr.p[:0] // clear the path
}

Expand Down Expand Up @@ -267,52 +267,79 @@ func (c *canvas) Start(width, height int) {
}
}

func (c *canvas) Path(d string, style Style) {
if d == "" {
func (c *canvas) Path(parts []string, style Style) {
if len(parts) == 0 {
return
}
var strokeDashArrayProperty string
if len(style.StrokeDashArray) > 0 {
strokeDashArrayProperty = c.getStrokeDashArray(style)
bb := bytes.NewBuffer(make([]byte, 0, 80))
bb.WriteString(`<path `)
c.writeStrokeDashArray(bb, style)
bb.WriteString(` d="`)
for i, p := range parts {
if i > 0 {
bb.WriteRune('\n')
}
bb.WriteString(p)
}
_, _ = c.w.Write([]byte(`<path ` + strokeDashArrayProperty + ` d="` + d + `" ` + c.styleAsSVG(style, false) + `/>`))
bb.WriteString(`" `)
c.styleAsSVG(bb, style, false)
bb.WriteString(`/>`)

_, _ = c.w.Write(bb.Bytes())
}

func (c *canvas) Text(x, y int, body string, style Style) {
if body == "" {
return
}
if c.textTheta == nil {
_, _ = c.w.Write([]byte(fmt.Sprintf(`<text x="%d" y="%d" %s>%s</text>`, x, y, c.styleAsSVG(style, true), body)))
} else {
transform := fmt.Sprintf(` transform="rotate(%0.2f,%d,%d)"`, RadiansToDegrees(*c.textTheta), x, y)
_, _ = c.w.Write([]byte(fmt.Sprintf(`<text x="%d" y="%d" %s%s>%s</text>`, x, y, c.styleAsSVG(style, true), transform, body)))
bb := bytes.NewBuffer(make([]byte, 0, 128))
bb.WriteString(`<text x="`)
bb.WriteString(strconv.Itoa(x))
bb.WriteString(`" y="`)
bb.WriteString(strconv.Itoa(y))
bb.WriteString(`" `)
c.styleAsSVG(bb, style, true)
if c.textTheta != nil {
bb.WriteString(fmt.Sprintf(` transform="rotate(%0.2f,%d,%d)"`, RadiansToDegrees(*c.textTheta), x, y))
}
bb.WriteRune('>')
bb.WriteString(body)
bb.WriteString("</text>")

_, _ = c.w.Write(bb.Bytes())
}

func (c *canvas) Circle(x, y, r int, style Style) {
_, _ = c.w.Write([]byte(fmt.Sprintf(`<circle cx="%d" cy="%d" r="%d" %s/>`, x, y, r, c.styleAsSVG(style, false))))
bb := bytes.NewBuffer(make([]byte, 0, 80))
bb.WriteString(`<circle cx="`)
bb.WriteString(strconv.Itoa(x))
bb.WriteString(`" cy="`)
bb.WriteString(strconv.Itoa(y))
bb.WriteString(`" r="`)
bb.WriteString(strconv.Itoa(r))
bb.WriteString(`" `)
c.styleAsSVG(bb, style, true)
bb.WriteString(`/>`)

_, _ = c.w.Write(bb.Bytes())
}

func (c *canvas) End() {
_, _ = c.w.Write([]byte("</svg>"))
}

// getStrokeDashArray returns the stroke-dasharray property of a style.
func (c *canvas) getStrokeDashArray(s Style) string {
// writeStrokeDashArray writes the stroke-dasharray property of a style.
func (c *canvas) writeStrokeDashArray(bb *bytes.Buffer, s Style) {
if len(s.StrokeDashArray) > 0 {
var sb strings.Builder
sb.WriteString("stroke-dasharray=\"")
bb.WriteString("stroke-dasharray=\"")
for i, v := range s.StrokeDashArray {
if i > 0 {
sb.WriteString(", ")
bb.WriteString(", ")
}
sb.WriteString(fmt.Sprintf("%0.1f", v))
bb.WriteString(fmt.Sprintf("%0.1f", v))
}
sb.WriteString("\"")
return sb.String()
bb.WriteString("\"")
}
return ""
}

// GetFontFace returns the font face for the style.
Expand All @@ -328,63 +355,66 @@ func (c *canvas) getFontFace(s Style) string {
}

// styleAsSVG returns the style as a svg style or class string.
func (c *canvas) styleAsSVG(s Style, applyText bool) string {
func (c *canvas) styleAsSVG(bb *bytes.Buffer, s Style, applyText bool) {
sw := s.StrokeWidth
sc := s.StrokeColor
fc := s.FillColor
fs := s.FontSize
fnc := s.FontColor

if s.ClassName != "" {
var sb strings.Builder
sb.WriteString("class=\"")
sb.WriteString(s.ClassName)
bb.WriteString("class=\"")
bb.WriteString(s.ClassName)
if !sc.IsZero() {
sb.WriteRune(' ')
sb.WriteString("stroke")
bb.WriteRune(' ')
bb.WriteString("stroke")
}
if !fc.IsZero() {
sb.WriteRune(' ')
sb.WriteString("fill")
bb.WriteRune(' ')
bb.WriteString("fill")
}
if applyText && (fs != 0 || s.Font != nil) {
sb.WriteRune(' ')
sb.WriteString("text")
bb.WriteRune(' ')
bb.WriteString("text")
}
sb.WriteString("\"")
return sb.String()
bb.WriteString("\"")
return
}

var pieces []string
bb.WriteString("style=\"")

if sw != 0 && !sc.IsTransparent() {
pieces = append(pieces, "stroke-width:"+formatFloatMinimized(sw))
pieces = append(pieces, "stroke:"+sc.String())
bb.WriteString("stroke-width:")
bb.WriteString(formatFloatMinimized(sw))
bb.WriteString(";stroke:")
bb.WriteString(sc.String())
} else {
pieces = append(pieces, "stroke:none")
bb.WriteString("stroke:none")
}

if applyText && !fnc.IsTransparent() {
pieces = append(pieces, "fill:"+fnc.String())
bb.WriteString(";fill:")
bb.WriteString(fnc.String())
} else if !fc.IsTransparent() {
pieces = append(pieces, "fill:"+fc.String())
bb.WriteString(";fill:")
bb.WriteString(fc.String())
} else {
pieces = append(pieces, "fill:none")
bb.WriteString(";fill:none")
}

if applyText {
if fs != 0 {
pieces = append(pieces, "font-size:"+formatFloatMinimized(drawing.PointsToPixels(c.dpi, fs))+"px")
bb.WriteString(";font-size:")
bb.WriteString(formatFloatMinimized(drawing.PointsToPixels(c.dpi, fs)))
bb.WriteString("px")
}
if s.Font != nil {
pieces = append(pieces, c.getFontFace(s))
bb.WriteRune(';')
bb.WriteString(c.getFontFace(s))
}
}

if len(pieces) == 0 {
return ""
}

return "style=\"" + strings.Join(pieces, ";") + "\""
bb.WriteRune('"')
}

// formatFloatNoTrailingZero formats a float without trailing zeros, so it is as small as possible.
Expand Down
12 changes: 9 additions & 3 deletions chartdraw/vector_renderer_test.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -65,7 +65,9 @@ func TestCanvasStyleSVG(t *testing.T) {

canvas := &canvas{dpi: DefaultDPI}

svgString := canvas.styleAsSVG(set, false)
var bb bytes.Buffer
canvas.styleAsSVG(&bb, set, false)
svgString := bb.String()
assert.NotEmpty(t, svgString)
assert.True(t, strings.HasPrefix(svgString, "style=\""))
assert.Contains(t, svgString, "stroke:white")
Expand All @@ -75,7 +77,9 @@ func TestCanvasStyleSVG(t *testing.T) {
assert.NotContains(t, svgString, "font-family")
assert.True(t, strings.HasSuffix(svgString, "\""))

svgString = canvas.styleAsSVG(set, true)
bb.Reset()
canvas.styleAsSVG(&bb, set, true)
svgString = bb.String()
assert.True(t, strings.HasPrefix(svgString, "style=\""))
assert.Contains(t, svgString, "stroke:white")
assert.Contains(t, svgString, "stroke-width:5")
Expand All @@ -94,7 +98,9 @@ func TestCanvasClassSVG(t *testing.T) {

canvas := &canvas{dpi: DefaultDPI}

assert.Equal(t, "class=\"test-class\"", canvas.styleAsSVG(set, false))
var bb bytes.Buffer
canvas.styleAsSVG(&bb, set, false)
assert.Equal(t, "class=\"test-class\"", bb.String())
}

func TestCanvasCustomInlineStylesheet(t *testing.T) {
Expand Down

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