func generateAtlas(font *truetype.Font, scale int32, dpi float64, width, height float32) ([]Vector4, *image.RGBA, []float32) {
var low rune = 32
var high rune = 127
glyphCount := int32(high - low + 1)
offsets := make([]float32, glyphCount)
bounds := font.Bounds(scale)
gw := float32(bounds.XMax - bounds.XMin)
gh := float32(bounds.YMax - bounds.YMin)
imageWidth := glh.Pow2(uint32(gw * float32(glyphCount)))
imageHeight := glh.Pow2(uint32(gh))
imageBounds := image.Rect(0, 0, int(imageWidth), int(imageHeight))
sx := float32(2) / width
sy := float32(2) / height
w := gw * sx
h := gh * sy
img := image.NewRGBA(imageBounds)
c := freetype.NewContext()
c.SetDst(img)
c.SetClip(img.Bounds())
c.SetSrc(image.White)
c.SetDPI(dpi)
c.SetFontSize(float64(scale))
c.SetFont(font)
var gi int32
var gx, gy float32
verts := make([]Vector4, 0)
texWidth := float32(img.Bounds().Dx())
texHeight := float32(img.Bounds().Dy())
for ch := low; ch <= high; ch++ {
index := font.Index(ch)
metric := font.HMetric(scale, index)
//the offset is used when drawing a string of glyphs - we will advance a glyph's quad by the width of all previous glyphs in the string
offsets[gi] = float32(metric.AdvanceWidth) * sx
//draw the glyph into the atlas at the correct location
pt := freetype.Pt(int(gx), int(gy)+int(c.PointToFix32(float64(scale))>>8))
c.DrawString(string(ch), pt)
tx1 := gx / texWidth
ty1 := gy / texHeight
tx2 := (gx + gw) / texWidth
ty2 := (gy + gh) / texHeight
//the x,y coordinates are the same for each quad; only the texture coordinates (stored in z,w) change.
//an optimization would be to only store texture coords, but I haven't figured that out yet
verts = append(verts, Vector4{-1, 1, tx1, ty1},
Vector4{-1 + (w), 1, tx2, ty1},
Vector4{-1, 1 - (h), tx1, ty2},
Vector4{-1 + (w), 1 - (h), tx2, ty2})
gx += gw
gi++
}
return verts, img, offsets
}
// Extents returns the FontExtents for a font.
// TODO needs to read this https://developer.apple.com/fonts/TrueType-Reference-Manual/RM02/Chap2.html#intro
func Extents(font *truetype.Font, size float64) FontExtents {
bounds := font.Bounds(font.FUnitsPerEm())
scale := size / float64(font.FUnitsPerEm())
return FontExtents{
Ascent: float64(bounds.YMax) * scale,
Descent: float64(bounds.YMin) * scale,
Height: float64(bounds.YMax-bounds.YMin) * scale,
}
}
func ExpectedSize(font *truetype.Font, s string) (int32, int32, error) {
c := freetype.NewContext()
c.SetDPI(dpi)
c.SetFont(font)
c.SetFontSize(size)
scale := size / float64(font.FUnitsPerEm())
prev := font.Index(rune(s[0]))
width := int32(font.HMetric(font.FUnitsPerEm(), prev).AdvanceWidth)
for _, char := range s[1:] {
index := font.Index(char)
width += int32(font.Kerning(font.FUnitsPerEm(), prev, index) +
font.HMetric(font.FUnitsPerEm(), index).AdvanceWidth)
prev = index
}
width = int32(float64(width) * scale)
bounds := font.Bounds(font.FUnitsPerEm())
height := int32(float64(bounds.YMax-bounds.YMin) * scale)
return width, height, nil
}
func genGlyphs(font *truetype.Font, size int, text string) (glyphs []*glyph) {
scale := int32(float64(size) * dpi * (64.0 / 72.0))
clip := image.Rect(0, 0, width, height)
// Calculate the rasterizer's bounds to handle the largest glyph.
b := font.Bounds(scale)
xmin := int(b.XMin) >> 6
ymin := -int(b.YMax) >> 6
xmax := int(b.XMax+63) >> 6
ymax := -int(b.YMin-63) >> 6
r := raster.NewRasterizer(xmax-xmin, ymax-ymin)
buf := truetype.NewGlyphBuf()
for _, variant := range []string{strings.ToUpper(text), strings.ToLower(text)} {
pt := Pt(30, 10+int(pointToFix32(float64(size))>>8))
for _, char := range variant {
idx := font.Index(char)
buf.Load(font, scale, idx, truetype.FullHinting)
// Calculate the integer-pixel bounds for the glyph.
xmin := int(raster.Fix32(buf.B.XMin<<2)) >> 8
ymin := int(-raster.Fix32(buf.B.YMax<<2)) >> 8
xmax := int(raster.Fix32(buf.B.XMax<<2)+0xff) >> 8
ymax := int(-raster.Fix32(buf.B.YMin<<2)+0xff) >> 8
fx := raster.Fix32(-xmin << 8)
fy := raster.Fix32(-ymin << 8)
ix := int(pt.X >> 8)
iy := int(pt.Y >> 8)
// Rasterize the glyph's vectors.
r.Clear()
e0 := 0
for _, e1 := range buf.End {
drawContour(r, buf.Point[e0:e1], fx, fy)
e0 = e1
}
mask := image.NewAlpha(image.Rect(0, 0, xmax-xmin, ymax-ymin))
r.Rasterize(raster.NewAlphaSrcPainter(mask))
pt.X += raster.Fix32(buf.AdvanceWidth << 2)
offset := image.Point{xmin + ix, ymin + iy}
glyphRect := mask.Bounds().Add(offset)
dr := clip.Intersect(glyphRect)
mp := image.Point{0, dr.Min.Y - glyphRect.Min.Y}
glyphs = append(glyphs, &glyph{
mask: mask,
mp: mp,
dr: dr,
})
}
}
return
}