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>
diff --git a/font/font.go b/font/font.go
index a089e77..a0a66d2 100644
--- a/font/font.go
+++ b/font/font.go
@@ -13,6 +13,7 @@
"image"
"image/draw"
"io"
+ "unicode/utf8"
"golang.org/x/image/math/fixed"
)
@@ -87,9 +88,6 @@
Descent fixed.Int26_6
}
-// TODO: Drawer.Layout or Drawer.Measure methods to measure text without
-// drawing?
-
// Drawer draws text on a destination image.
//
// A Drawer is not safe for concurrent use by multiple goroutines, since its
@@ -115,19 +113,25 @@
// 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
// 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)
-// and the last case can't assume that you can rewind the stream.
+// TODO: do we assume that the input is in any particular Unicode Normalization
+// 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
// vertical line? Should DrawString return the number of runes drawn?
-// DrawString draws s at the dot and advances the dot's location.
-func (d *Drawer) DrawString(s string) {
- var prevC rune
- for i, c := range s {
- if i != 0 {
+// DrawBytes draws s at the dot and advances the dot's location.
+func (d *Drawer) DrawBytes(s []byte) {
+ prevC := rune(-1)
+ for len(s) > 0 {
+ c, size := utf8.DecodeRune(s)
+ s = s[size:]
+ if prevC >= 0 {
d.Dot.X += d.Face.Kern(prevC, c)
}
dr, mask, maskp, advance, ok := d.Face.Glyph(d.Dot, c)
@@ -143,16 +147,63 @@
}
}
+// 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.
func (d *Drawer) MeasureString(s string) (advance fixed.Int26_6) {
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.
func MeasureString(f Face, s string) (advance fixed.Int26_6) {
- var prevC rune
- for i, c := range s {
- if i != 0 {
+ prevC := rune(-1)
+ for _, c := range s {
+ if prevC >= 0 {
advance += f.Kern(prevC, c)
}
a, ok := f.GlyphAdvance(c)
