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// Copyright 2017 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package opentype implements the font.Face interface based on SFNT
// font file formats.
package opentype // import "golang.org/x/image/font/opentype"
import (
"image"
"image/draw"
"golang.org/x/image/font"
"golang.org/x/image/font/sfnt"
"golang.org/x/image/math/fixed"
"golang.org/x/image/vector"
)
// FaceOptions describes the possible options given to NewFace when
// creating a new font.Face from a sfnt.Font.
type FaceOptions struct {
Size float64 // Size is the font size in points
DPI float64 // DPI is the dots per inch resolution
Hinting font.Hinting // Hinting selects how to quantize a vector font's glyph nodes
}
func defaultFaceOptions() *FaceOptions {
return &FaceOptions{
Size: 12,
DPI: 72,
Hinting: font.HintingNone,
}
}
// Face implements the font.Face interface for sfnt.Font values.
type Face struct {
f *sfnt.Font
hinting font.Hinting
scale fixed.Int26_6
metrics font.Metrics
metricsSet bool
buf sfnt.Buffer
rast vector.Rasterizer
mask image.Alpha
}
// NewFace returns a new font.Face for the given sfnt.Font.
// if opts is nil, sensible defaults will be used.
func NewFace(f *sfnt.Font, opts *FaceOptions) (font.Face, error) {
if opts == nil {
opts = defaultFaceOptions()
}
face := &Face{
f: f,
hinting: opts.Hinting,
scale: fixed.Int26_6(0.5 + (opts.Size * opts.DPI * 64 / 72)),
}
return face, nil
}
// Close satisfies the font.Face interface.
func (f *Face) Close() error {
return nil
}
// Metrics satisfies the font.Face interface.
func (f *Face) Metrics() font.Metrics {
if !f.metricsSet {
var err error
f.metrics, err = f.f.Metrics(&f.buf, f.scale, f.hinting)
if err != nil {
f.metrics = font.Metrics{}
}
f.metricsSet = true
}
return f.metrics
}
// Kern satisfies the font.Face interface.
func (f *Face) Kern(r0, r1 rune) fixed.Int26_6 {
x0 := f.index(r0)
x1 := f.index(r1)
k, err := f.f.Kern(&f.buf, x0, x1, fixed.Int26_6(f.f.UnitsPerEm()), f.hinting)
if err != nil {
return 0
}
return k
}
// Glyph satisfies the font.Face interface.
func (f *Face) Glyph(dot fixed.Point26_6, r rune) (dr image.Rectangle, mask image.Image, maskp image.Point, advance fixed.Int26_6, ok bool) {
x, err := f.f.GlyphIndex(&f.buf, r)
if err != nil {
return image.Rectangle{}, nil, image.Point{}, 0, false
}
// Call f.f.GlyphAdvance before f.f.LoadGlyph because the LoadGlyph docs
// say this about the &f.buf argument: the segments become invalid to use
// once [the buffer] is re-used.
advance, err = f.f.GlyphAdvance(&f.buf, x, f.scale, f.hinting)
if err != nil {
return image.Rectangle{}, nil, image.Point{}, 0, false
}
segments, err := f.f.LoadGlyph(&f.buf, x, f.scale, nil)
if err != nil {
return image.Rectangle{}, nil, image.Point{}, 0, false
}
// Numerical notation used below:
// - 2 is an integer, "two"
// - 2:16 is a 26.6 fixed point number, "two and a quarter"
// - 2.5 is a float32 number, "two and a half"
// Using 26.6 fixed point numbers means that there are 64 sub-pixel units
// in 1 integer pixel unit.
// Translate the sub-pixel bounding box from glyph space (where the glyph
// origin is at (0:00, 0:00)) to dst space (where the glyph origin is at
// the dot). dst space is the coordinate space that contains both the dot
// (a sub-pixel position) and dr (an integer-pixel rectangle).
dBounds := segments.Bounds().Add(dot)
// Quantize the sub-pixel bounds (dBounds) to integer-pixel bounds (dr).
dr.Min.X = dBounds.Min.X.Floor()
dr.Min.Y = dBounds.Min.Y.Floor()
dr.Max.X = dBounds.Max.X.Ceil()
dr.Max.Y = dBounds.Max.Y.Ceil()
width := dr.Dx()
height := dr.Dy()
if width < 0 || height < 0 {
return image.Rectangle{}, nil, image.Point{}, 0, false
}
// Calculate the sub-pixel bias to convert from glyph space to rasterizer
// space. In glyph space, the segments may be to the left or right and
// above or below the glyph origin. In rasterizer space, the segments
// should only be right and below (or equal to) the top-left corner (0.0,
// 0.0). They should also be left and above (or equal to) the bottom-right
// corner (width, height), as the rasterizer should enclose the glyph
// bounding box.
//
// For example, suppose that dot.X was at the sub-pixel position 25:48,
// three quarters of the way into the 26th pixel, and that bounds.Min.X was
// 1:20. We then have dBounds.Min.X = 1:20 + 25:48 = 27:04, dr.Min.X = 27
// and biasX = 25:48 - 27:00 = -1:16. A vertical stroke at 1:20 in glyph
// space becomes (1:20 + -1:16) = 0:04 in rasterizer space. 0:04 as a
// fixed.Int26_6 value is float32(4)/64.0 = 0.0625 as a float32 value.
biasX := dot.X - fixed.Int26_6(dr.Min.X<<6)
biasY := dot.Y - fixed.Int26_6(dr.Min.Y<<6)
// Configure the mask image, re-allocating its buffer if necessary.
nPixels := width * height
if cap(f.mask.Pix) < nPixels {
f.mask.Pix = make([]uint8, 2*nPixels)
}
f.mask.Pix = f.mask.Pix[:nPixels]
f.mask.Stride = width
f.mask.Rect.Min.X = 0
f.mask.Rect.Min.Y = 0
f.mask.Rect.Max.X = width
f.mask.Rect.Max.Y = height
// Rasterize the biased segments, converting from fixed.Int26_6 to float32.
f.rast.Reset(width, height)
f.rast.DrawOp = draw.Src
for _, seg := range segments {
switch seg.Op {
case sfnt.SegmentOpMoveTo:
f.rast.MoveTo(
float32(seg.Args[0].X+biasX)/64,
float32(seg.Args[0].Y+biasY)/64,
)
case sfnt.SegmentOpLineTo:
f.rast.LineTo(
float32(seg.Args[0].X+biasX)/64,
float32(seg.Args[0].Y+biasY)/64,
)
case sfnt.SegmentOpQuadTo:
f.rast.QuadTo(
float32(seg.Args[0].X+biasX)/64,
float32(seg.Args[0].Y+biasY)/64,
float32(seg.Args[1].X+biasX)/64,
float32(seg.Args[1].Y+biasY)/64,
)
case sfnt.SegmentOpCubeTo:
f.rast.CubeTo(
float32(seg.Args[0].X+biasX)/64,
float32(seg.Args[0].Y+biasY)/64,
float32(seg.Args[1].X+biasX)/64,
float32(seg.Args[1].Y+biasY)/64,
float32(seg.Args[2].X+biasX)/64,
float32(seg.Args[2].Y+biasY)/64,
)
}
}
f.rast.Draw(&f.mask, f.mask.Bounds(), image.Opaque, image.Point{})
return dr, &f.mask, f.mask.Rect.Min, advance, true
}
// GlyphBounds satisfies the font.Face interface.
func (f *Face) GlyphBounds(r rune) (bounds fixed.Rectangle26_6, advance fixed.Int26_6, ok bool) {
bounds, advance, err := f.f.GlyphBounds(&f.buf, f.index(r), f.scale, f.hinting)
return bounds, advance, err == nil
}
// GlyphAdvance satisfies the font.Face interface.
func (f *Face) GlyphAdvance(r rune) (advance fixed.Int26_6, ok bool) {
advance, err := f.f.GlyphAdvance(&f.buf, f.index(r), f.scale, f.hinting)
return advance, err == nil
}
func (f *Face) index(r rune) sfnt.GlyphIndex {
x, _ := f.f.GlyphIndex(&f.buf, r)
return x
}