func (ig *ImageGraphics) TextLen(s string, font chart.Font) int {
c := freetype.NewContext()
c.SetDPI(dpi)
c.SetFont(ig.font)
fontsize := ig.relFontsizeToPixel(font.Size)
c.SetFontSize(fontsize)
scale := int32(fontsize * dpi * (64.0 / 72.0))
var p raster.Point
prev, hasPrev := truetype.Index(0), false
for _, rune := range s {
index := ig.font.Index(rune)
if hasPrev {
p.X += raster.Fix32(ig.font.Kerning(scale, prev, index)) << 2
}
p.X += raster.Fix32(ig.font.HMetric(scale, index).AdvanceWidth) << 2
prev, hasPrev = index, true
}
return int((p.X + 127) / 256)
}
// textBox renders t into a tight fitting image
func (ig *ImageGraphics) textBox(t string, font chart.Font) image.Image {
// Initialize the context.
fg := image.NewUniform(color.Alpha{0xff})
bg := image.NewUniform(color.Alpha{0x00})
width := ig.TextLen(t, font)
size := ig.relFontsizeToPixel(font.Size)
bb := ig.font.Bounds(int32(size))
// TODO: Ugly, manual, heuristic hack to get "nicer" text for common latin characters
bb.YMin++
if size >= 15 {
bb.YMin++
bb.YMax--
}
if size >= 20 {
bb.YMax--
}
if size >= 25 {
bb.YMin++
bb.YMax--
}
dy := int(bb.YMax - bb.YMin)
canvas := image.NewAlpha(image.Rect(0, 0, width, dy))
draw.Draw(canvas, canvas.Bounds(), bg, image.ZP, draw.Src)
c := freetype.NewContext()
c.SetDPI(dpi)
c.SetFont(ig.font)
c.SetFontSize(size)
c.SetClip(canvas.Bounds())
c.SetDst(canvas)
c.SetSrc(fg)
// Draw the text.
pt := freetype.Pt(0, dy+int(bb.YMin)-1)
extent, err := c.DrawString(t, pt)
if err != nil {
log.Println(err)
return nil
}
// log.Printf("text %q, extent: %v", t, extent)
return canvas.SubImage(image.Rect(0, 0, int((extent.X+127)/256), dy))
}