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vgsvg.go
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vgsvg.go
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// Copyright ©2015 The Gonum Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package vgsvg uses svgo (github.com/ajstarks/svgo)
// as a backend for vg.
package vgsvg // import "gonum.org/v1/plot/vg/vgsvg"
import (
"bufio"
"bytes"
"encoding/base64"
"fmt"
"html"
"image"
"image/color"
"image/png"
"io"
"math"
svgo "github.com/ajstarks/svgo"
"gonum.org/v1/plot/vg"
)
// pr is the precision to use when outputting float64s.
const pr = 5
const (
// DefaultWidth and DefaultHeight are the default canvas
// dimensions.
DefaultWidth = 4 * vg.Inch
DefaultHeight = 4 * vg.Inch
)
type Canvas struct {
svg *svgo.SVG
w, h vg.Length
buf *bytes.Buffer
stack []context
}
type context struct {
color color.Color
dashArray []vg.Length
dashOffset vg.Length
lineWidth vg.Length
gEnds int
}
type option func(*Canvas)
// UseWH specifies the width and height of the canvas.
func UseWH(w, h vg.Length) option {
return func(c *Canvas) {
if w <= 0 || h <= 0 {
panic("vgsvg: w and h must both be > 0")
}
c.w = w
c.h = h
}
}
// New returns a new image canvas.
func New(w, h vg.Length) *Canvas {
return NewWith(UseWH(w, h))
}
// NewWith returns a new image canvas created according to the specified
// options. The currently accepted options is UseWH. If size is not
// specified, the default is used.
func NewWith(opts ...option) *Canvas {
buf := new(bytes.Buffer)
c := &Canvas{
svg: svgo.New(buf),
w: DefaultWidth,
h: DefaultHeight,
buf: buf,
stack: []context{{}},
}
for _, opt := range opts {
opt(c)
}
// This is like svg.Start, except it uses floats
// and specifies the units.
fmt.Fprintf(c.buf, `<?xml version="1.0"?>
<!-- Generated by SVGo and Plotinum VG -->
<svg width="%.*gpt" height="%.*gpt" viewBox="0 0 %.*g %.*g"
xmlns="http://www.w3.org/2000/svg"
xmlns:xlink="http://www.w3.org/1999/xlink">`+"\n",
pr, c.w,
pr, c.h,
pr, c.w,
pr, c.h,
)
// Swap the origin to the bottom left.
// This must be matched with a </g> when saving,
// before the closing </svg>.
c.svg.Gtransform(fmt.Sprintf("scale(1, -1) translate(0, -%.*g)", pr, c.h.Points()))
vg.Initialize(c)
return c
}
func (c *Canvas) Size() (w, h vg.Length) {
return c.w, c.h
}
func (c *Canvas) context() *context {
return &c.stack[len(c.stack)-1]
}
func (c *Canvas) SetLineWidth(w vg.Length) {
c.context().lineWidth = w
}
func (c *Canvas) SetLineDash(dashes []vg.Length, offs vg.Length) {
c.context().dashArray = dashes
c.context().dashOffset = offs
}
func (c *Canvas) SetColor(clr color.Color) {
c.context().color = clr
}
func (c *Canvas) Rotate(rot float64) {
rot = rot * 180 / math.Pi
c.svg.Rotate(rot)
c.context().gEnds++
}
func (c *Canvas) Translate(pt vg.Point) {
c.svg.Gtransform(fmt.Sprintf("translate(%.*g, %.*g)", pr, pt.X.Points(), pr, pt.Y.Points()))
c.context().gEnds++
}
func (c *Canvas) Scale(x, y float64) {
c.svg.ScaleXY(x, y)
c.context().gEnds++
}
func (c *Canvas) Push() {
top := *c.context()
top.gEnds = 0
c.stack = append(c.stack, top)
}
func (c *Canvas) Pop() {
for i := 0; i < c.context().gEnds; i++ {
c.svg.Gend()
}
c.stack = c.stack[:len(c.stack)-1]
}
func (c *Canvas) Stroke(path vg.Path) {
if c.context().lineWidth.Points() <= 0 {
return
}
c.svg.Path(c.pathData(path),
style(elm("fill", "#000000", "none"),
elm("stroke", "none", colorString(c.context().color)),
elm("stroke-opacity", "1", opacityString(c.context().color)),
elm("stroke-width", "1", "%.*g", pr, c.context().lineWidth.Points()),
elm("stroke-dasharray", "none", dashArrayString(c)),
elm("stroke-dashoffset", "0", "%.*g", pr, c.context().dashOffset.Points())))
}
func (c *Canvas) Fill(path vg.Path) {
c.svg.Path(c.pathData(path),
style(elm("fill", "#000000", colorString(c.context().color)),
elm("fill-opacity", "1", opacityString(c.context().color))))
}
func (c *Canvas) pathData(path vg.Path) string {
buf := new(bytes.Buffer)
var x, y float64
for _, comp := range path {
switch comp.Type {
case vg.MoveComp:
fmt.Fprintf(buf, "M%.*g,%.*g", pr, comp.Pos.X.Points(), pr, comp.Pos.Y.Points())
x = comp.Pos.X.Points()
y = comp.Pos.Y.Points()
case vg.LineComp:
fmt.Fprintf(buf, "L%.*g,%.*g", pr, comp.Pos.X.Points(), pr, comp.Pos.Y.Points())
x = comp.Pos.X.Points()
y = comp.Pos.Y.Points()
case vg.ArcComp:
r := comp.Radius.Points()
x0 := comp.Pos.X.Points() + r*math.Cos(comp.Start)
y0 := comp.Pos.Y.Points() + r*math.Sin(comp.Start)
if x0 != x || y0 != y {
fmt.Fprintf(buf, "L%.*g,%.*g", pr, x0, pr, y0)
}
if math.Abs(comp.Angle) >= 2*math.Pi {
x, y = circle(buf, c, &comp)
} else {
x, y = arc(buf, c, &comp)
}
case vg.CurveComp:
switch len(comp.Control) {
case 1:
fmt.Fprintf(buf, "Q%.*g,%.*g,%.*g,%.*g",
pr, comp.Control[0].X.Points(), pr, comp.Control[0].Y.Points(),
pr, comp.Pos.X.Points(), pr, comp.Pos.Y.Points())
case 2:
fmt.Fprintf(buf, "C%.*g,%.*g,%.*g,%.*g,%.*g,%.*g",
pr, comp.Control[0].X.Points(), pr, comp.Control[0].Y.Points(),
pr, comp.Control[1].X.Points(), pr, comp.Control[1].Y.Points(),
pr, comp.Pos.X.Points(), pr, comp.Pos.Y.Points())
default:
panic("vgsvg: invalid number of control points")
}
x = comp.Pos.X.Points()
y = comp.Pos.Y.Points()
case vg.CloseComp:
buf.WriteString("Z")
default:
panic(fmt.Sprintf("vgsvg: unknown path component type: %d", comp.Type))
}
}
return buf.String()
}
// circle adds circle path data to the given writer.
// Circles must be drawn using two arcs because
// SVG disallows the start and end point of an arc
// from being at the same location.
func circle(w io.Writer, c *Canvas, comp *vg.PathComp) (x, y float64) {
angle := 2 * math.Pi
if comp.Angle < 0 {
angle = -2 * math.Pi
}
angle += remainder(comp.Angle, 2*math.Pi)
if angle >= 4*math.Pi {
panic("Impossible angle")
}
r := comp.Radius.Points()
x0 := comp.Pos.X.Points() + r*math.Cos(comp.Start+angle/2)
y0 := comp.Pos.Y.Points() + r*math.Sin(comp.Start+angle/2)
x = comp.Pos.X.Points() + r*math.Cos(comp.Start+angle)
y = comp.Pos.Y.Points() + r*math.Sin(comp.Start+angle)
fmt.Fprintf(w, "A%.*g,%.*g 0 %d %d %.*g,%.*g", pr, r, pr, r,
large(angle/2), sweep(angle/2), pr, x0, pr, y0) //
fmt.Fprintf(w, "A%.*g,%.*g 0 %d %d %.*g,%.*g", pr, r, pr, r,
large(angle/2), sweep(angle/2), pr, x, pr, y)
return
}
// remainder returns the remainder of x/y.
// We don't use math.Remainder because it
// seems to return incorrect values due to how
// IEEE defines the remainder operation…
func remainder(x, y float64) float64 {
return (x/y - math.Trunc(x/y)) * y
}
// arc adds arc path data to the given writer.
// Arc can only be used if the arc's angle is
// less than a full circle, if it is greater then
// circle should be used instead.
func arc(w io.Writer, c *Canvas, comp *vg.PathComp) (x, y float64) {
r := comp.Radius.Points()
x = comp.Pos.X.Points() + r*math.Cos(comp.Start+comp.Angle)
y = comp.Pos.Y.Points() + r*math.Sin(comp.Start+comp.Angle)
fmt.Fprintf(w, "A%.*g,%.*g 0 %d %d %.*g,%.*g", pr, r, pr, r,
large(comp.Angle), sweep(comp.Angle), pr, x, pr, y)
return
}
// sweep returns the arc sweep flag value for
// the given angle.
func sweep(a float64) int {
if a < 0 {
return 0
}
return 1
}
// large returns the arc's large flag value for
// the given angle.
func large(a float64) int {
if math.Abs(a) >= math.Pi {
return 1
}
return 0
}
// FillString draws str at position pt using the specified font.
// Text passed to FillString is escaped with html.EscapeString.
func (c *Canvas) FillString(font vg.Font, pt vg.Point, str string) {
fontStr, ok := fontMap[font.Name()]
if !ok {
panic(fmt.Sprintf("Unknown font: %s", font.Name()))
}
sty := style(fontStr,
elm("font-size", "medium", "%.*gpx", pr, font.Size.Points()),
elm("fill", "#000000", colorString(c.context().color)))
if sty != "" {
sty = "\n\t" + sty
}
fmt.Fprintf(c.buf, `<text x="%.*g" y="%.*g" transform="scale(1, -1)"%s>%s</text>`+"\n",
pr, pt.X.Points(), pr, -pt.Y.Points(), sty, html.EscapeString(str))
}
// DrawImage implements the vg.Canvas.DrawImage method.
func (c *Canvas) DrawImage(rect vg.Rectangle, img image.Image) {
buf := new(bytes.Buffer)
err := png.Encode(buf, img)
if err != nil {
panic(fmt.Errorf("vgsvg: error encoding image to PNG: %+v", err))
}
str := "data:image/jpg;base64," + base64.StdEncoding.EncodeToString(buf.Bytes())
rsz := rect.Size()
min := rect.Min
var (
width = rsz.X.Points()
height = rsz.Y.Points()
xmin = min.X.Points()
ymin = min.Y.Points()
)
fmt.Fprintf(
c.buf,
`<image x="%v" y="%v" width="%v" height="%v" xlink:href="%s" %s />`+"\n",
xmin,
-ymin-height,
width,
height,
str,
// invert y so image is not upside-down
`transform="scale(1, -1)"`,
)
}
var (
// fontMap maps Postscript-style font names to their
// corresponding SVG style string.
fontMap = map[string]string{
"Courier": "font-family:Courier;font-weight:normal;font-style:normal",
"Courier-Bold": "font-family:Courier;font-weight:bold;font-style:normal",
"Courier-Oblique": "font-family:Courier;font-weight:normal;font-style:oblique",
"Courier-BoldOblique": "font-family:Courier;font-weight:bold;font-style:oblique",
"Helvetica": "font-family:Helvetica;font-weight:normal;font-style:normal",
"Helvetica-Bold": "font-family:Helvetica;font-weight:bold;font-style:normal",
"Helvetica-Oblique": "font-family:Helvetica;font-weight:normal;font-style:oblique",
"Helvetica-BoldOblique": "font-family:Helvetica;font-weight:bold;font-style:oblique",
"Times-Roman": "font-family:Times;font-weight:normal;font-style:normal",
"Times-Bold": "font-family:Times;font-weight:bold;font-style:normal",
"Times-Italic": "font-family:Times;font-weight:normal;font-style:italic",
"Times-BoldItalic": "font-family:Times;font-weight:bold;font-style:italic",
}
)
// WriteTo writes the canvas to an io.Writer.
func (c *Canvas) WriteTo(w io.Writer) (int64, error) {
b := bufio.NewWriter(w)
n, err := c.buf.WriteTo(b)
if err != nil {
return n, err
}
// Close the groups and svg in the output buffer
// so that the Canvas is not closed and can be
// used again if needed.
for i := 0; i < c.nEnds(); i++ {
m, err := fmt.Fprintln(b, "</g>")
n += int64(m)
if err != nil {
return n, err
}
}
m, err := fmt.Fprintln(b, "</svg>")
n += int64(m)
if err != nil {
return n, err
}
return n, b.Flush()
}
// nEnds returns the number of group ends
// needed before the SVG is saved.
func (c *Canvas) nEnds() int {
n := 1 // close the transform that moves the origin
for _, ctx := range c.stack {
n += ctx.gEnds
}
return n
}
// style returns a style string composed of
// all of the given elements. If the elements
// are all empty then the empty string is
// returned.
func style(elms ...string) string {
str := ""
for _, e := range elms {
if e == "" {
continue
}
if str != "" {
str += ";"
}
str += e
}
if str == "" {
return ""
}
return "style=\"" + str + "\""
}
// elm returns a style element string with the
// given key and value. If the value matches
// default then the empty string is returned.
func elm(key, def, f string, vls ...interface{}) string {
value := fmt.Sprintf(f, vls...)
if value == def {
return ""
}
return key + ":" + value
}
// dashArrayString returns a string representing the
// dash array specification.
func dashArrayString(c *Canvas) string {
str := ""
for i, d := range c.context().dashArray {
str += fmt.Sprintf("%.*g", pr, d.Points())
if i < len(c.context().dashArray)-1 {
str += ","
}
}
if str == "" {
str = "none"
}
return str
}
// colorString returns the hexadecimal string representation of the color
func colorString(clr color.Color) string {
if clr == nil {
clr = color.Black
}
r, g, b, _a := clr.RGBA()
a := 255.0 / float64(_a)
return fmt.Sprintf("#%02X%02X%02X", int(float64(r)*a),
int(float64(g)*a), int(float64(b)*a))
}
// opacityString returns the opacity value of the given color.
func opacityString(clr color.Color) string {
if clr == nil {
clr = color.Black
}
_, _, _, a := clr.RGBA()
return fmt.Sprintf("%.*g", pr, float64(a)/math.MaxUint16)
}