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font: have Glyph return !ok for U+FFFD substitute
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The other return values may still be non-zero, but this lets callers
identify when substitution happens.

"TODO: is falling back on the U+FFFD glyph the responsibility of the
Drawer or the Face?" was resolved. The answer is "the Face". For
kerning, the previous rune is unchanged (and not set to U+FFFD).

This also fixes an inconsistency in the basicfont.Face implementation,
where GlyphAdvance and GlyphBounds would unconditionally return a
non-zero advance, but Glyph could return a zero advance when the Face
doesn't have a U+FFFD entry.

Fixes golang/go#58252

Change-Id: Ie97e68e1d5e2efd13c9e84ad12db4495d83a5ca3
Reviewed-on: https://go-review.googlesource.com/c/image/+/474376
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Nigel Tao (INACTIVE; USE @golang.org INSTEAD) <nigeltao@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Run-TryBot: Nigel Tao <nigeltao@golang.org>
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nigeltao committed Mar 21, 2023
1 parent b6ac75b commit 08ca817
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Showing 3 changed files with 75 additions and 88 deletions.
65 changes: 37 additions & 28 deletions font/basicfont/basicfont.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -89,41 +89,50 @@ func (f *Face) Metrics() font.Metrics {
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) {

loop:
for _, rr := range [2]rune{r, '\ufffd'} {
for _, rng := range f.Ranges {
if rr < rng.Low || rng.High <= rr {
continue
}
maskp.Y = (int(rr-rng.Low) + rng.Offset) * (f.Ascent + f.Descent)
ok = true
break loop
if found, rng := f.find(r); rng != nil {
maskp.Y = (int(found-rng.Low) + rng.Offset) * (f.Ascent + f.Descent)
x := int(dot.X+32)>>6 + f.Left
y := int(dot.Y+32) >> 6
dr = image.Rectangle{
Min: image.Point{
X: x,
Y: y - f.Ascent,
},
Max: image.Point{
X: x + f.Width,
Y: y + f.Descent,
},
}
}
if !ok {
return image.Rectangle{}, nil, image.Point{}, 0, false
}

x := int(dot.X+32)>>6 + f.Left
y := int(dot.Y+32) >> 6
dr = image.Rectangle{
Min: image.Point{
X: x,
Y: y - f.Ascent,
},
Max: image.Point{
X: x + f.Width,
Y: y + f.Descent,
},
return dr, f.Mask, maskp, fixed.I(f.Advance), r == found
}

return dr, f.Mask, maskp, fixed.I(f.Advance), true
return image.Rectangle{}, nil, image.Point{}, 0, false
}

func (f *Face) GlyphBounds(r rune) (bounds fixed.Rectangle26_6, advance fixed.Int26_6, ok bool) {
return fixed.R(0, -f.Ascent, f.Width, +f.Descent), fixed.I(f.Advance), true
if found, rng := f.find(r); rng != nil {
return fixed.R(0, -f.Ascent, f.Width, +f.Descent), fixed.I(f.Advance), r == found
}
return fixed.Rectangle26_6{}, 0, false
}

func (f *Face) GlyphAdvance(r rune) (advance fixed.Int26_6, ok bool) {
return fixed.I(f.Advance), true
if found, rng := f.find(r); rng != nil {
return fixed.I(f.Advance), r == found
}
return 0, false
}

func (f *Face) find(r rune) (rune, *Range) {
for {
for i, rng := range f.Ranges {
if (rng.Low <= r) && (r < rng.High) {
return r, &f.Ranges[i]
}
}
if r == '\ufffd' {
return 0, nil
}
r = '\ufffd'
}
}
79 changes: 30 additions & 49 deletions font/font.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -38,7 +38,10 @@ type Face interface {
// glyph at the sub-pixel destination location dot, and that glyph's
// advance width.
//
// It returns !ok if the face does not contain a glyph for r.
// It returns !ok if the face does not contain a glyph for r. This includes
// returning !ok for a fallback glyph (such as substituting a U+FFFD glyph
// or OpenType's .notdef glyph), in which case the other return values may
// still be non-zero.
//
// The contents of the mask image returned by one Glyph call may change
// after the next Glyph call. Callers that want to cache the mask must make
Expand All @@ -49,7 +52,10 @@ type Face interface {
// GlyphBounds returns the bounding box of r's glyph, drawn at a dot equal
// to the origin, and that glyph's advance width.
//
// It returns !ok if the face does not contain a glyph for r.
// It returns !ok if the face does not contain a glyph for r. This includes
// returning !ok for a fallback glyph (such as substituting a U+FFFD glyph
// or OpenType's .notdef glyph), in which case the other return values may
// still be non-zero.
//
// The glyph's ascent and descent are equal to -bounds.Min.Y and
// +bounds.Max.Y. The glyph's left-side and right-side bearings are equal
Expand All @@ -60,7 +66,10 @@ type Face interface {

// GlyphAdvance returns the advance width of r's glyph.
//
// It returns !ok if the face does not contain a glyph for r.
// It returns !ok if the face does not contain a glyph for r. This includes
// returning !ok for a fallback glyph (such as substituting a U+FFFD glyph
// or OpenType's .notdef glyph), in which case the other return values may
// still be non-zero.
GlyphAdvance(r rune) (advance fixed.Int26_6, ok bool)

// Kern returns the horizontal adjustment for the kerning pair (r0, r1). A
Expand Down Expand Up @@ -150,14 +159,10 @@ func (d *Drawer) DrawBytes(s []byte) {
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
dr, mask, maskp, advance, _ := d.Face.Glyph(d.Dot, c)
if !dr.Empty() {
draw.DrawMask(d.Dst, dr, d.Src, image.Point{}, mask, maskp, draw.Over)
}
draw.DrawMask(d.Dst, dr, d.Src, image.Point{}, mask, maskp, draw.Over)
d.Dot.X += advance
prevC = c
}
Expand All @@ -170,14 +175,10 @@ func (d *Drawer) DrawString(s string) {
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
dr, mask, maskp, advance, _ := d.Face.Glyph(d.Dot, c)
if !dr.Empty() {
draw.DrawMask(d.Dst, dr, d.Src, image.Point{}, mask, maskp, draw.Over)
}
draw.DrawMask(d.Dst, dr, d.Src, image.Point{}, mask, maskp, draw.Over)
d.Dot.X += advance
prevC = c
}
Expand Down Expand Up @@ -227,16 +228,12 @@ func BoundBytes(f Face, s []byte) (bounds fixed.Rectangle26_6, advance fixed.Int
if prevC >= 0 {
advance += f.Kern(prevC, c)
}
b, a, ok := f.GlyphBounds(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
b, a, _ := f.GlyphBounds(c)
if !b.Empty() {
b.Min.X += advance
b.Max.X += advance
bounds = bounds.Union(b)
}
b.Min.X += advance
b.Max.X += advance
bounds = bounds.Union(b)
advance += a
prevC = c
}
Expand All @@ -251,16 +248,12 @@ func BoundString(f Face, s string) (bounds fixed.Rectangle26_6, advance fixed.In
if prevC >= 0 {
advance += f.Kern(prevC, c)
}
b, a, ok := f.GlyphBounds(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
b, a, _ := f.GlyphBounds(c)
if !b.Empty() {
b.Min.X += advance
b.Max.X += advance
bounds = bounds.Union(b)
}
b.Min.X += advance
b.Max.X += advance
bounds = bounds.Union(b)
advance += a
prevC = c
}
Expand All @@ -278,13 +271,7 @@ func MeasureBytes(f Face, s []byte) (advance fixed.Int26_6) {
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
}
a, _ := f.GlyphAdvance(c)
advance += a
prevC = c
}
Expand All @@ -298,13 +285,7 @@ func MeasureString(f Face, s string) (advance fixed.Int26_6) {
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
}
a, _ := f.GlyphAdvance(c)
advance += a
prevC = c
}
Expand Down
19 changes: 8 additions & 11 deletions font/opentype/opentype.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -133,8 +133,8 @@ func (f *Face) Metrics() font.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)
x0, _ := f.f.GlyphIndex(&f.buf, r0)
x1, _ := f.f.GlyphIndex(&f.buf, r1)
k, err := f.f.Kern(&f.buf, x0, x1, fixed.Int26_6(f.f.UnitsPerEm()), f.hinting)
if err != nil {
return 0
Expand Down Expand Up @@ -251,22 +251,19 @@ func (f *Face) Glyph(dot fixed.Point26_6, r rune) (dr image.Rectangle, mask imag
}
f.rast.Draw(&f.mask, f.mask.Bounds(), image.Opaque, image.Point{})

return dr, &f.mask, f.mask.Rect.Min, advance, true
return dr, &f.mask, f.mask.Rect.Min, advance, x != 0
}

// 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
x, _ := f.f.GlyphIndex(&f.buf, r)
bounds, advance, err := f.f.GlyphBounds(&f.buf, x, f.scale, f.hinting)
return bounds, advance, (err == nil) && (x != 0)
}

// 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
advance, err := f.f.GlyphAdvance(&f.buf, x, f.scale, f.hinting)
return advance, (err == nil) && (x != 0)
}

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