go-chart/raster_renderer.go

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package chart
import (
"image"
"image/color"
"image/png"
"io"
"github.com/golang/freetype/truetype"
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"github.com/wcharczuk/go-chart/drawing"
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)
// PNG returns a new png/raster renderer.
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func PNG(width, height int) (Renderer, error) {
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i := image.NewRGBA(image.Rect(0, 0, width, height))
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gc, err := drawing.NewRasterGraphicContext(i)
if err == nil {
return &rasterRenderer{
i: i,
gc: gc,
}, nil
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}
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return nil, err
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}
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// rasterRenderer renders chart commands to a bitmap.
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type rasterRenderer struct {
i *image.RGBA
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gc *drawing.RasterGraphicContext
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fontSize float64
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fontColor color.Color
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f *truetype.Font
}
// SetDPI implements the interface method.
func (rr *rasterRenderer) SetDPI(dpi float64) {
rr.gc.SetDPI(dpi)
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}
// SetStrokeColor implements the interface method.
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func (rr *rasterRenderer) SetStrokeColor(c drawing.Color) {
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rr.gc.SetStrokeColor(c)
}
// SetFillColor implements the interface method.
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func (rr *rasterRenderer) SetFillColor(c drawing.Color) {
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rr.gc.SetFillColor(c)
}
// SetLineWidth implements the interface method.
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func (rr *rasterRenderer) SetStrokeWidth(width float64) {
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rr.gc.SetLineWidth(width)
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}
// MoveTo implements the interface method.
func (rr *rasterRenderer) MoveTo(x, y int) {
rr.gc.MoveTo(float64(x), float64(y))
}
// LineTo implements the interface method.
func (rr *rasterRenderer) LineTo(x, y int) {
rr.gc.LineTo(float64(x), float64(y))
}
// Close implements the interface method.
func (rr *rasterRenderer) Close() {
rr.gc.Close()
}
// Stroke implements the interface method.
func (rr *rasterRenderer) Stroke() {
rr.gc.Stroke()
}
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// Fill implements the interface method.
func (rr *rasterRenderer) Fill() {
rr.gc.Fill()
}
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// FillStroke implements the interface method.
func (rr *rasterRenderer) FillStroke() {
rr.gc.FillStroke()
}
// Circle implements the interface method.
func (rr *rasterRenderer) Circle(radius float64, x, y int) {
xf := float64(x)
yf := float64(y)
rr.gc.MoveTo(xf-radius, yf) //9
rr.gc.QuadCurveTo(xf, yf, xf, yf-radius) //12
rr.gc.QuadCurveTo(xf, yf, xf+radius, yf) //3
rr.gc.QuadCurveTo(xf, yf, xf, yf+radius) //6
rr.gc.QuadCurveTo(xf, yf, xf-radius, yf) //9
rr.gc.Close()
rr.gc.FillStroke()
}
// SetFont implements the interface method.
func (rr *rasterRenderer) SetFont(f *truetype.Font) {
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rr.f = f
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rr.gc.SetFont(f)
}
// SetFontSize implements the interface method.
func (rr *rasterRenderer) SetFontSize(size float64) {
rr.fontSize = size
rr.gc.SetFontSize(size)
}
// SetFontColor implements the interface method.
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func (rr *rasterRenderer) SetFontColor(c drawing.Color) {
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rr.fontColor = c
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rr.gc.SetFillColor(c)
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rr.gc.SetStrokeColor(c)
}
// Text implements the interface method.
func (rr *rasterRenderer) Text(body string, x, y int) {
rr.gc.CreateStringPath(body, float64(x), float64(y))
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rr.gc.Fill()
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}
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// MeasureText returns the height and width in pixels of a string.
func (rr *rasterRenderer) MeasureText(body string) (width int, height int) {
l, t, r, b, err := rr.gc.GetStringBounds(body)
if err != nil {
return
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}
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dw := r - l
dh := b - t
width = int(drawing.PointsToPixels(rr.gc.GetDPI(), dw))
height = int(drawing.PointsToPixels(rr.gc.GetDPI(), dh))
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return
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}
// Save implements the interface method.
func (rr *rasterRenderer) Save(w io.Writer) error {
return png.Encode(w, rr.i)
}