vector_renderer.go

package chart

import (
	"bytes"
	"fmt"
	"io"
	"math"
	"strings"

	"golang.org/x/image/font"

	"github.com/golang/freetype/truetype"
	"github.com/wcharczuk/go-chart/drawing"
)

// SVG returns a new png/raster renderer.
func SVG(width, height int) (Renderer, error) {
	buffer := bytes.NewBuffer([]byte{})
	canvas := newCanvas(buffer)
	canvas.Start(width, height)
	return &vectorRenderer{
		b: buffer,
		c: canvas,
		s: &Style{},
		p: []string{},
	}, nil
}

// vectorRenderer renders chart commands to a bitmap.
type vectorRenderer struct {
	dpi float64
	b   *bytes.Buffer
	c   *canvas
	s   *Style
	p   []string
	fc  *font.Drawer
}

// GetDPI returns the dpi.
func (vr *vectorRenderer) GetDPI() float64 {
	return vr.dpi
}

// SetDPI implements the interface method.
func (vr *vectorRenderer) SetDPI(dpi float64) {
	vr.dpi = dpi
	vr.c.dpi = dpi
}

// SetStrokeColor implements the interface method.
func (vr *vectorRenderer) SetStrokeColor(c drawing.Color) {
	vr.s.StrokeColor = c
}

// SetFillColor implements the interface method.
func (vr *vectorRenderer) SetFillColor(c drawing.Color) {
	vr.s.FillColor = c
}

// SetLineWidth implements the interface method.
func (vr *vectorRenderer) SetStrokeWidth(width float64) {
	vr.s.StrokeWidth = width
}

// StrokeDashArray sets the stroke dash array.
func (vr *vectorRenderer) SetStrokeDashArray(dashArray []float64) {
	vr.s.StrokeDashArray = dashArray
}

// MoveTo implements the interface method.
func (vr *vectorRenderer) MoveTo(x, y int) {
	vr.p = append(vr.p, fmt.Sprintf("M %d %d", x, y))
}

// LineTo implements the interface method.
func (vr *vectorRenderer) LineTo(x, y int) {
	vr.p = append(vr.p, fmt.Sprintf("L %d %d", x, y))
}

// QuadCurveTo draws a quad curve.
func (vr *vectorRenderer) QuadCurveTo(cx, cy, x, y int) {
	vr.p = append(vr.p, fmt.Sprintf("Q%d,%d %d,%d", cx, cy, x, y))
}

func (vr *vectorRenderer) ArcTo(cx, cy int, rx, ry, startAngle, delta float64) {
	startAngle = RadianAdd(startAngle, _pi2)
	endAngle := RadianAdd(startAngle, delta)

	startx := cx + int(rx*math.Sin(startAngle))
	starty := cy - int(ry*math.Cos(startAngle))

	if len(vr.p) > 0 {
		vr.p = append(vr.p, fmt.Sprintf("L %d %d", startx, starty))
	} else {
		vr.p = append(vr.p, fmt.Sprintf("M %d %d", startx, starty))
	}

	endx := cx + int(rx*math.Sin(endAngle))
	endy := cy - int(ry*math.Cos(endAngle))

	dd := RadiansToDegrees(delta)

	vr.p = append(vr.p, fmt.Sprintf("A %d %d %0.2f 0 1 %d %d", int(rx), int(ry), dd, endx, endy))
}

// Close closes a shape.
func (vr *vectorRenderer) Close() {
	vr.p = append(vr.p, fmt.Sprintf("Z"))
}

// Stroke draws the path with no fill.
func (vr *vectorRenderer) Stroke() {
	vr.drawPath(vr.s.SVGStroke())
}

// Fill draws the path with no stroke.
func (vr *vectorRenderer) Fill() {
	vr.drawPath(vr.s.SVGFill())
}

// FillStroke draws the path with both fill and stroke.
func (vr *vectorRenderer) FillStroke() {
	s := vr.s.SVGFillAndStroke()
	vr.drawPath(s)
}

// drawPath draws a path.
func (vr *vectorRenderer) drawPath(s Style) {
	vr.c.Path(strings.Join(vr.p, "\n"), &s)
	vr.p = []string{} // clear the path
}

// Circle implements the interface method.
func (vr *vectorRenderer) Circle(radius float64, x, y int) {
	style := vr.s.SVGFillAndStroke()
	vr.c.Circle(x, y, int(radius), &style)
}

// SetFont implements the interface method.
func (vr *vectorRenderer) SetFont(f *truetype.Font) {
	vr.s.Font = f
}

// SetFontColor implements the interface method.
func (vr *vectorRenderer) SetFontColor(c drawing.Color) {
	vr.s.FontColor = c
}

// SetFontSize implements the interface method.
func (vr *vectorRenderer) SetFontSize(size float64) {
	vr.s.FontSize = size
}

// Text draws a text blob.
func (vr *vectorRenderer) Text(body string, x, y int) {
	style := vr.s.SVGText()
	vr.c.Text(x, y, body, &style)
}

// MeasureText uses the truetype font drawer to measure the width of text.
func (vr *vectorRenderer) MeasureText(body string) (box Box) {
	if vr.s.GetFont() != nil {
		vr.fc = &font.Drawer{
			Face: truetype.NewFace(vr.s.GetFont(), &truetype.Options{
				DPI:  vr.dpi,
				Size: vr.s.FontSize,
			}),
		}
		w := vr.fc.MeasureString(body).Ceil()

		box.Right = w
		box.Bottom = int(drawing.PointsToPixels(vr.dpi, vr.s.FontSize))
	}
	return
}

// Save saves the renderer's contents to a writer.
func (vr *vectorRenderer) Save(w io.Writer) error {
	vr.c.End()
	_, err := w.Write(vr.b.Bytes())
	return err
}

func newCanvas(w io.Writer) *canvas {
	return &canvas{
		w: w,
	}
}

type canvas struct {
	w      io.Writer
	dpi    float64
	width  int
	height int
}

func (c *canvas) Start(width, height int) {
	c.width = width
	c.height = height
	c.w.Write([]byte(fmt.Sprintf(`<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="%d" height="%d">\n`, c.width, c.height)))
}

func (c *canvas) Path(d string, style *Style) {
	var strokeDashArrayProperty string
	if len(style.StrokeDashArray) > 0 {
		strokeDashArrayProperty = style.SVGStrokeDashArray()
	}
	c.w.Write([]byte(fmt.Sprintf(`<path %s d="%s" style="%s"/>\n`, strokeDashArrayProperty, d, style.SVG(c.dpi))))
}

func (c *canvas) Text(x, y int, body string, style *Style) {
	c.w.Write([]byte(fmt.Sprintf(`<text x="%d" y="%d" style="%s">%s</text>`, x, y, style.SVG(c.dpi), body)))
}

func (c *canvas) Circle(x, y, r int, style *Style) {
	c.w.Write([]byte(fmt.Sprintf(`<circle cx="%d" cy="%d" r="%d" style="%s">`, x, y, r, style.SVG(c.dpi))))
}

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