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