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font/basicfont: add Descent and Left fields.

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A face's glyph height (the height of the glyph image) isn't necessarily
the inter-line spacing: f.Ascent + f.Descent isn't always f.Height.

Similarly, a face's glyph image's left side isn't always dot.X.

Change-Id: I86594c52b8d31bf652ac34a695e9270ac635a5bc
Reviewed-on: https://go-review.googlesource.com/24481
Reviewed-by: David Crawshaw <crawshaw@golang.org>
This commit is contained in:
Nigel Tao 2016-06-26 16:21:54 +10:00
parent 97680175a5
commit c4226c0d9c
1 changed files with 18 additions and 14 deletions
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32
font/basicfont/basicfont.go
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@ -19,8 +19,8 @@ import (
// exclusive on the high end.
//
// If Low <= r && r < High, then the rune r is mapped to the sub-image of
// Face.Mask whose bounds are image.Rect(0, y, Face.Width, y+Face.Height),
// where y equals (int(r-Low) + Offset) * Face.Height.
// Face.Mask whose bounds are image.Rect(0, y*h, Face.Width, (y+1)*h),
// where y = (int(r-Low) + Offset) and h = (Face.Ascent + Face.Descent).
type Range struct {
Low, High rune
Offset int
@ -38,6 +38,7 @@ var Face7x13 = &Face{
Width: 6,
Height: 13,
Ascent: 11,
Descent: 2,
Mask: mask7x13,
Ranges: []Range{
{'\u0020', '\u007f', 0},
@ -53,12 +54,15 @@ type Face struct {
Advance int
// Width is the glyph width, in pixels.
Width int
// Height is the glyph height, in pixels.
// Height is the inter-line height, in pixels.
Height int
// Ascent is the glyph ascent, in pixels.
Ascent int
// TODO: do we also need Top and Left fields?
// Descent is the glyph descent, in pixels.
Descent int
// Left is the left side bearing, in pixels. A positive value means that
// all of a glyph is to the right of the dot.
Left int
// Mask contains all of the glyph masks. Its width is typically the Face's
// Width, and its height a multiple of the Face's Height.
@ -75,7 +79,7 @@ func (f *Face) Metrics() font.Metrics {
return font.Metrics{
Height: fixed.I(f.Height),
Ascent: fixed.I(f.Ascent),
Descent: fixed.I(f.Height - f.Ascent),
Descent: fixed.I(f.Descent),
}
}
@ -88,7 +92,7 @@ loop:
if rr < rng.Low || rng.High <= rr {
continue
}
maskp.Y = (int(rr-rng.Low) + rng.Offset) * f.Height
maskp.Y = (int(rr-rng.Low) + rng.Offset) * (f.Ascent + f.Descent)
ok = true
break loop
}
@ -97,16 +101,16 @@ loop:
return image.Rectangle{}, nil, image.Point{}, 0, false
}
minX := int(dot.X+32) >> 6
minY := int(dot.Y+32)>>6 - f.Ascent
x := int(dot.X+32)>>6 + f.Left
y := int(dot.Y+32) >> 6
dr = image.Rectangle{
Min: image.Point{
X: minX,
Y: minY,
X: x,
Y: y - f.Ascent,
},
Max: image.Point{
X: minX + f.Width,
Y: minY + f.Height,
X: x + f.Width,
Y: y + f.Descent,
},
}
@ -114,7 +118,7 @@ loop:
}
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.Ascent+f.Height), fixed.I(f.Advance), true
return fixed.R(0, -f.Ascent, f.Width, +f.Descent), fixed.I(f.Advance), true
}
func (f *Face) GlyphAdvance(r rune) (advance fixed.Int26_6, ok bool) {