freetype/truetype/face.go

508 lines
13 KiB
Go
Raw Normal View History

// Copyright 2015 The Freetype-Go Authors. All rights reserved.
// Use of this source code is governed by your choice of either the
// FreeType License or the GNU General Public License version 2 (or
// any later version), both of which can be found in the LICENSE file.
package truetype
import (
"image"
"math"
2018-11-14 09:38:19 +00:00
"git.fromouter.space/crunchy-rocks/freetype/raster"
"golang.org/x/image/font"
"golang.org/x/image/math/fixed"
)
func powerOf2(i int) bool {
return i != 0 && (i&(i-1)) == 0
}
// Options are optional arguments to NewFace.
type Options struct {
// Size is the font size in points, as in "a 10 point font size".
//
// A zero value means to use a 12 point font size.
Size float64
// DPI is the dots-per-inch resolution.
//
// A zero value means to use 72 DPI.
DPI float64
// Hinting is how to quantize the glyph nodes.
//
// A zero value means to use no hinting.
Hinting font.Hinting
// GlyphCacheEntries is the number of entries in the glyph mask image
// cache.
//
// If non-zero, it must be a power of 2.
//
// A zero value means to use 512 entries.
GlyphCacheEntries int
// SubPixelsX is the number of sub-pixel locations a glyph's dot is
// quantized to, in the horizontal direction. For example, a value of 8
// means that the dot is quantized to 1/8th of a pixel. This quantization
// only affects the glyph mask image, not its bounding box or advance
// width. A higher value gives a more faithful glyph image, but reduces the
// effectiveness of the glyph cache.
//
// If non-zero, it must be a power of 2, and be between 1 and 64 inclusive.
//
// A zero value means to use 4 sub-pixel locations.
SubPixelsX int
// SubPixelsY is the number of sub-pixel locations a glyph's dot is
// quantized to, in the vertical direction. For example, a value of 8
// means that the dot is quantized to 1/8th of a pixel. This quantization
// only affects the glyph mask image, not its bounding box or advance
// width. A higher value gives a more faithful glyph image, but reduces the
// effectiveness of the glyph cache.
//
// If non-zero, it must be a power of 2, and be between 1 and 64 inclusive.
//
// A zero value means to use 1 sub-pixel location.
SubPixelsY int
}
func (o *Options) size() float64 {
if o != nil && o.Size > 0 {
return o.Size
}
return 12
}
func (o *Options) dpi() float64 {
if o != nil && o.DPI > 0 {
return o.DPI
}
return 72
}
func (o *Options) hinting() font.Hinting {
if o != nil {
switch o.Hinting {
case font.HintingVertical, font.HintingFull:
// TODO: support vertical hinting.
return font.HintingFull
}
}
return font.HintingNone
}
func (o *Options) glyphCacheEntries() int {
if o != nil && powerOf2(o.GlyphCacheEntries) {
return o.GlyphCacheEntries
}
// 512 is 128 * 4 * 1, which lets us cache 128 glyphs at 4 * 1 subpixel
// locations in the X and Y direction.
return 512
}
func (o *Options) subPixelsX() (value uint32, halfQuantum, mask fixed.Int26_6) {
if o != nil {
switch o.SubPixelsX {
case 1, 2, 4, 8, 16, 32, 64:
return subPixels(o.SubPixelsX)
}
}
// This default value of 4 isn't based on anything scientific, merely as
// small a number as possible that looks almost as good as no quantization,
// or returning subPixels(64).
return subPixels(4)
}
func (o *Options) subPixelsY() (value uint32, halfQuantum, mask fixed.Int26_6) {
if o != nil {
switch o.SubPixelsX {
case 1, 2, 4, 8, 16, 32, 64:
return subPixels(o.SubPixelsX)
}
}
// This default value of 1 isn't based on anything scientific, merely that
// vertical sub-pixel glyph rendering is pretty rare. Baseline locations
// can usually afford to snap to the pixel grid, so the vertical direction
// doesn't have the deal with the horizontal's fractional advance widths.
return subPixels(1)
}
// subPixels returns q and the bias and mask that leads to q quantized
// sub-pixel locations per full pixel.
//
// For example, q == 4 leads to a bias of 8 and a mask of 0xfffffff0, or -16,
// because we want to round fractions of fixed.Int26_6 as:
// - 0 to 7 rounds to 0.
// - 8 to 23 rounds to 16.
// - 24 to 39 rounds to 32.
// - 40 to 55 rounds to 48.
// - 56 to 63 rounds to 64.
// which means to add 8 and then bitwise-and with -16, in two's complement
// representation.
//
// When q == 1, we want bias == 32 and mask == -64.
// When q == 2, we want bias == 16 and mask == -32.
// When q == 4, we want bias == 8 and mask == -16.
// ...
// When q == 64, we want bias == 0 and mask == -1. (The no-op case).
// The pattern is clear.
func subPixels(q int) (value uint32, bias, mask fixed.Int26_6) {
return uint32(q), 32 / fixed.Int26_6(q), -64 / fixed.Int26_6(q)
}
// glyphCacheEntry caches the arguments and return values of rasterize.
type glyphCacheEntry struct {
key glyphCacheKey
val glyphCacheVal
}
type glyphCacheKey struct {
index Index
fx, fy uint8
}
type glyphCacheVal struct {
advanceWidth fixed.Int26_6
offset image.Point
gw int
gh int
}
type indexCacheEntry struct {
rune rune
index Index
}
// NewFace returns a new font.Face for the given Font.
func NewFace(f *Font, opts *Options) font.Face {
a := &face{
f: f,
hinting: opts.hinting(),
scale: fixed.Int26_6(0.5 + (opts.size() * opts.dpi() * 64 / 72)),
glyphCache: make([]glyphCacheEntry, opts.glyphCacheEntries()),
}
a.subPixelX, a.subPixelBiasX, a.subPixelMaskX = opts.subPixelsX()
a.subPixelY, a.subPixelBiasY, a.subPixelMaskY = opts.subPixelsY()
// Fill the cache with invalid entries. Valid glyph cache entries have fx
// and fy in the range [0, 64). Valid index cache entries have rune >= 0.
for i := range a.glyphCache {
a.glyphCache[i].key.fy = 0xff
}
for i := range a.indexCache {
a.indexCache[i].rune = -1
}
// Set the rasterizer's bounds to be big enough to handle the largest glyph.
b := f.Bounds(a.scale)
xmin := +int(b.Min.X) >> 6
ymin := -int(b.Max.Y) >> 6
xmax := +int(b.Max.X+63) >> 6
ymax := -int(b.Min.Y-63) >> 6
a.maxw = xmax - xmin
a.maxh = ymax - ymin
a.masks = image.NewAlpha(image.Rect(0, 0, a.maxw, a.maxh*len(a.glyphCache)))
a.r.SetBounds(a.maxw, a.maxh)
a.p = facePainter{a}
return a
}
type face struct {
f *Font
hinting font.Hinting
scale fixed.Int26_6
subPixelX uint32
subPixelBiasX fixed.Int26_6
subPixelMaskX fixed.Int26_6
subPixelY uint32
subPixelBiasY fixed.Int26_6
subPixelMaskY fixed.Int26_6
masks *image.Alpha
glyphCache []glyphCacheEntry
r raster.Rasterizer
p raster.Painter
paintOffset int
maxw int
maxh int
glyphBuf GlyphBuf
indexCache [indexCacheLen]indexCacheEntry
// TODO: clip rectangle?
}
const indexCacheLen = 256
func (a *face) index(r rune) Index {
const mask = indexCacheLen - 1
c := &a.indexCache[r&mask]
if c.rune == r {
return c.index
}
i := a.f.Index(r)
c.rune = r
c.index = i
return i
}
// Close satisfies the font.Face interface.
func (a *face) Close() error { return nil }
// Metrics satisfies the font.Face interface.
func (a *face) Metrics() font.Metrics {
scale := float64(a.scale)
fupe := float64(a.f.FUnitsPerEm())
return font.Metrics{
Height: a.scale,
Ascent: fixed.Int26_6(math.Ceil(scale * float64(+a.f.ascent) / fupe)),
Descent: fixed.Int26_6(math.Ceil(scale * float64(-a.f.descent) / fupe)),
}
}
// Kern satisfies the font.Face interface.
func (a *face) Kern(r0, r1 rune) fixed.Int26_6 {
i0 := a.index(r0)
i1 := a.index(r1)
2015-08-24 06:17:16 +00:00
kern := a.f.Kern(a.scale, i0, i1)
if a.hinting != font.HintingNone {
kern = (kern + 32) &^ 63
}
return kern
}
// Glyph satisfies the font.Face interface.
func (a *face) Glyph(dot fixed.Point26_6, r rune) (
dr image.Rectangle, mask image.Image, maskp image.Point, advance fixed.Int26_6, ok bool) {
// Quantize to the sub-pixel granularity.
dotX := (dot.X + a.subPixelBiasX) & a.subPixelMaskX
dotY := (dot.Y + a.subPixelBiasY) & a.subPixelMaskY
// Split the coordinates into their integer and fractional parts.
ix, fx := int(dotX>>6), dotX&0x3f
iy, fy := int(dotY>>6), dotY&0x3f
index := a.index(r)
cIndex := uint32(index)
cIndex = cIndex*a.subPixelX - uint32(fx/a.subPixelMaskX)
cIndex = cIndex*a.subPixelY - uint32(fy/a.subPixelMaskY)
cIndex &= uint32(len(a.glyphCache) - 1)
a.paintOffset = a.maxh * int(cIndex)
k := glyphCacheKey{
index: index,
fx: uint8(fx),
fy: uint8(fy),
}
var v glyphCacheVal
if a.glyphCache[cIndex].key != k {
var ok bool
v, ok = a.rasterize(index, fx, fy)
if !ok {
return image.Rectangle{}, nil, image.Point{}, 0, false
}
a.glyphCache[cIndex] = glyphCacheEntry{k, v}
} else {
v = a.glyphCache[cIndex].val
}
dr.Min = image.Point{
X: ix + v.offset.X,
Y: iy + v.offset.Y,
}
dr.Max = image.Point{
X: dr.Min.X + v.gw,
Y: dr.Min.Y + v.gh,
}
return dr, a.masks, image.Point{Y: a.paintOffset}, v.advanceWidth, true
}
func (a *face) GlyphBounds(r rune) (bounds fixed.Rectangle26_6, advance fixed.Int26_6, ok bool) {
if err := a.glyphBuf.Load(a.f, a.scale, a.index(r), a.hinting); err != nil {
return fixed.Rectangle26_6{}, 0, false
}
xmin := +a.glyphBuf.Bounds.Min.X
ymin := -a.glyphBuf.Bounds.Max.Y
xmax := +a.glyphBuf.Bounds.Max.X
ymax := -a.glyphBuf.Bounds.Min.Y
if xmin > xmax || ymin > ymax {
return fixed.Rectangle26_6{}, 0, false
}
return fixed.Rectangle26_6{
Min: fixed.Point26_6{
X: xmin,
Y: ymin,
},
Max: fixed.Point26_6{
X: xmax,
Y: ymax,
},
}, a.glyphBuf.AdvanceWidth, true
}
func (a *face) GlyphAdvance(r rune) (advance fixed.Int26_6, ok bool) {
if err := a.glyphBuf.Load(a.f, a.scale, a.index(r), a.hinting); err != nil {
return 0, false
}
return a.glyphBuf.AdvanceWidth, true
}
// rasterize returns the advance width, integer-pixel offset to render at, and
// the width and height of the given glyph at the given sub-pixel offsets.
//
// The 26.6 fixed point arguments fx and fy must be in the range [0, 1).
func (a *face) rasterize(index Index, fx, fy fixed.Int26_6) (v glyphCacheVal, ok bool) {
if err := a.glyphBuf.Load(a.f, a.scale, index, a.hinting); err != nil {
return glyphCacheVal{}, false
}
// Calculate the integer-pixel bounds for the glyph.
xmin := int(fx+a.glyphBuf.Bounds.Min.X) >> 6
ymin := int(fy-a.glyphBuf.Bounds.Max.Y) >> 6
xmax := int(fx+a.glyphBuf.Bounds.Max.X+0x3f) >> 6
ymax := int(fy-a.glyphBuf.Bounds.Min.Y+0x3f) >> 6
if xmin > xmax || ymin > ymax {
return glyphCacheVal{}, false
}
// A TrueType's glyph's nodes can have negative co-ordinates, but the
// rasterizer clips anything left of x=0 or above y=0. xmin and ymin are
// the pixel offsets, based on the font's FUnit metrics, that let a
// negative co-ordinate in TrueType space be non-negative in rasterizer
// space. xmin and ymin are typically <= 0.
fx -= fixed.Int26_6(xmin << 6)
fy -= fixed.Int26_6(ymin << 6)
// Rasterize the glyph's vectors.
a.r.Clear()
pixOffset := a.paintOffset * a.maxw
clear(a.masks.Pix[pixOffset : pixOffset+a.maxw*a.maxh])
e0 := 0
for _, e1 := range a.glyphBuf.Ends {
a.drawContour(a.glyphBuf.Points[e0:e1], fx, fy)
e0 = e1
}
a.r.Rasterize(a.p)
return glyphCacheVal{
a.glyphBuf.AdvanceWidth,
image.Point{xmin, ymin},
xmax - xmin,
ymax - ymin,
}, true
}
func clear(pix []byte) {
for i := range pix {
pix[i] = 0
}
}
// drawContour draws the given closed contour with the given offset.
func (a *face) drawContour(ps []Point, dx, dy fixed.Int26_6) {
if len(ps) == 0 {
return
}
// The low bit of each point's Flags value is whether the point is on the
// curve. Truetype fonts only have quadratic Bézier curves, not cubics.
// Thus, two consecutive off-curve points imply an on-curve point in the
// middle of those two.
//
// See http://chanae.walon.org/pub/ttf/ttf_glyphs.htm for more details.
// ps[0] is a truetype.Point measured in FUnits and positive Y going
// upwards. start is the same thing measured in fixed point units and
// positive Y going downwards, and offset by (dx, dy).
start := fixed.Point26_6{
X: dx + ps[0].X,
Y: dy - ps[0].Y,
}
var others []Point
if ps[0].Flags&0x01 != 0 {
others = ps[1:]
} else {
last := fixed.Point26_6{
X: dx + ps[len(ps)-1].X,
Y: dy - ps[len(ps)-1].Y,
}
if ps[len(ps)-1].Flags&0x01 != 0 {
start = last
others = ps[:len(ps)-1]
} else {
start = fixed.Point26_6{
X: (start.X + last.X) / 2,
Y: (start.Y + last.Y) / 2,
}
others = ps
}
}
a.r.Start(start)
q0, on0 := start, true
for _, p := range others {
q := fixed.Point26_6{
X: dx + p.X,
Y: dy - p.Y,
}
on := p.Flags&0x01 != 0
if on {
if on0 {
a.r.Add1(q)
} else {
a.r.Add2(q0, q)
}
} else {
if on0 {
// No-op.
} else {
mid := fixed.Point26_6{
X: (q0.X + q.X) / 2,
Y: (q0.Y + q.Y) / 2,
}
a.r.Add2(q0, mid)
}
}
q0, on0 = q, on
}
// Close the curve.
if on0 {
a.r.Add1(start)
} else {
a.r.Add2(q0, start)
}
}
// facePainter is like a raster.AlphaSrcPainter, with an additional Y offset
// (face.paintOffset) to the painted spans.
type facePainter struct {
a *face
}
func (p facePainter) Paint(ss []raster.Span, done bool) {
m := p.a.masks
b := m.Bounds()
b.Min.Y = p.a.paintOffset
b.Max.Y = p.a.paintOffset + p.a.maxh
for _, s := range ss {
s.Y += p.a.paintOffset
if s.Y < b.Min.Y {
continue
}
if s.Y >= b.Max.Y {
return
}
if s.X0 < b.Min.X {
s.X0 = b.Min.X
}
if s.X1 > b.Max.X {
s.X1 = b.Max.X
}
if s.X0 >= s.X1 {
continue
}
base := (s.Y-m.Rect.Min.Y)*m.Stride - m.Rect.Min.X
p := m.Pix[base+s.X0 : base+s.X1]
color := uint8(s.Alpha >> 8)
for i := range p {
p[i] = color
}
}
}