font: add a []byte flavor of string methods.

Change-Id: I2506067ba6ac12c275b65c3a52cb38579d4b9dca
Reviewed-on: https://go-review.googlesource.com/23464
Reviewed-by: David Crawshaw <crawshaw@golang.org>
This commit is contained in:
Nigel Tao 2016-05-26 15:28:50 +10:00
parent 51ddfee6f3
commit 97680175a5

View File

@ -13,6 +13,7 @@ import (
"image" "image"
"image/draw" "image/draw"
"io" "io"
"unicode/utf8"
"golang.org/x/image/math/fixed" "golang.org/x/image/math/fixed"
) )
@ -87,9 +88,6 @@ type Metrics struct {
Descent fixed.Int26_6 Descent fixed.Int26_6
} }
// TODO: Drawer.Layout or Drawer.Measure methods to measure text without
// drawing?
// Drawer draws text on a destination image. // Drawer draws text on a destination image.
// //
// A Drawer is not safe for concurrent use by multiple goroutines, since its // A Drawer is not safe for concurrent use by multiple goroutines, since its
@ -115,19 +113,25 @@ type Drawer struct {
// TODO: should DrawString return the last rune drawn, so the next DrawString // TODO: should DrawString return the last rune drawn, so the next DrawString
// call can kern beforehand? Or should that be the responsibility of the caller // call can kern beforehand? Or should that be the responsibility of the caller
// if they really want to do that, since they have to explicitly shift d.Dot // if they really want to do that, since they have to explicitly shift d.Dot
// anyway? // anyway? What if ligatures span more than two runes? What if grapheme
// clusters span multiple runes?
// //
// In general, we'd have a DrawBytes([]byte) and DrawRuneReader(io.RuneReader) // TODO: do we assume that the input is in any particular Unicode Normalization
// and the last case can't assume that you can rewind the stream. // Form?
//
// TODO: have DrawRunes(s []rune)? DrawRuneReader(io.RuneReader)?? If we take
// io.RuneReader, we can't assume that we can rewind the stream.
// //
// TODO: how does this work with line breaking: drawing text up until a // TODO: how does this work with line breaking: drawing text up until a
// vertical line? Should DrawString return the number of runes drawn? // vertical line? Should DrawString return the number of runes drawn?
// DrawString draws s at the dot and advances the dot's location. // DrawBytes draws s at the dot and advances the dot's location.
func (d *Drawer) DrawString(s string) { func (d *Drawer) DrawBytes(s []byte) {
var prevC rune prevC := rune(-1)
for i, c := range s { for len(s) > 0 {
if i != 0 { c, size := utf8.DecodeRune(s)
s = s[size:]
if prevC >= 0 {
d.Dot.X += d.Face.Kern(prevC, c) d.Dot.X += d.Face.Kern(prevC, c)
} }
dr, mask, maskp, advance, ok := d.Face.Glyph(d.Dot, c) dr, mask, maskp, advance, ok := d.Face.Glyph(d.Dot, c)
@ -143,16 +147,63 @@ func (d *Drawer) DrawString(s string) {
} }
} }
// DrawString draws s at the dot and advances the dot's location.
func (d *Drawer) DrawString(s string) {
prevC := rune(-1)
for _, c := range s {
if prevC >= 0 {
d.Dot.X += d.Face.Kern(prevC, c)
}
dr, mask, maskp, advance, ok := d.Face.Glyph(d.Dot, c)
if !ok {
// TODO: is falling back on the U+FFFD glyph the responsibility of
// the Drawer or the Face?
// TODO: set prevC = '\ufffd'?
continue
}
draw.DrawMask(d.Dst, dr, d.Src, image.Point{}, mask, maskp, draw.Over)
d.Dot.X += advance
prevC = c
}
}
// MeasureBytes returns how far dot would advance by drawing s.
func (d *Drawer) MeasureBytes(s []byte) (advance fixed.Int26_6) {
return MeasureBytes(d.Face, s)
}
// MeasureString returns how far dot would advance by drawing s. // MeasureString returns how far dot would advance by drawing s.
func (d *Drawer) MeasureString(s string) (advance fixed.Int26_6) { func (d *Drawer) MeasureString(s string) (advance fixed.Int26_6) {
return MeasureString(d.Face, s) return MeasureString(d.Face, s)
} }
// MeasureBytes returns how far dot would advance by drawing s with f.
func MeasureBytes(f Face, s []byte) (advance fixed.Int26_6) {
prevC := rune(-1)
for len(s) > 0 {
c, size := utf8.DecodeRune(s)
s = s[size:]
if prevC >= 0 {
advance += f.Kern(prevC, c)
}
a, ok := f.GlyphAdvance(c)
if !ok {
// TODO: is falling back on the U+FFFD glyph the responsibility of
// the Drawer or the Face?
// TODO: set prevC = '\ufffd'?
continue
}
advance += a
prevC = c
}
return advance
}
// MeasureString returns how far dot would advance by drawing s with f. // MeasureString returns how far dot would advance by drawing s with f.
func MeasureString(f Face, s string) (advance fixed.Int26_6) { func MeasureString(f Face, s string) (advance fixed.Int26_6) {
var prevC rune prevC := rune(-1)
for i, c := range s { for _, c := range s {
if i != 0 { if prevC >= 0 {
advance += f.Kern(prevC, c) advance += f.Kern(prevC, c)
} }
a, ok := f.GlyphAdvance(c) a, ok := f.GlyphAdvance(c)