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text: change line ascent and descent to fit font size #123

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text: change line ascent and descent to fit font size #123

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15 changes: 11 additions & 4 deletions text/gotext.go
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Original file line number Diff line number Diff line change
Expand Up @@ -895,11 +895,18 @@ func toLine(faceToIndex map[font.Font]int, o shaping.Line, dir system.TextDirect
}
line.runeCount += run.Runes.Count
line.width += run.Advance
if line.ascent < run.LineBounds.Ascent {
line.ascent = run.LineBounds.Ascent

// fix ascent to make all glyphes (CJK or not) always in same baseline
// fixedDescent + fixedAscent should equal fontSize
scale := fixedToFloat(run.Size) / fixedToFloat(run.LineBounds.LineHeight())
fixedAscent := floatToFixed(fixedToFloat(run.LineBounds.Ascent) * scale)
fixedDescent := floatToFixed(fixedToFloat(-run.LineBounds.Descent+run.LineBounds.Gap) * scale)

if line.ascent < fixedAscent {
line.ascent = fixedAscent
}
if line.descent < -run.LineBounds.Descent+run.LineBounds.Gap {
line.descent = -run.LineBounds.Descent + run.LineBounds.Gap
if line.descent < fixedDescent {
line.descent = fixedDescent
}
}
line.lineHeight = maxSize
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34 changes: 32 additions & 2 deletions text/gotext_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -52,14 +52,44 @@ func TestEmptyString(t *testing.T) {
t.Fatalf("Layout returned no lines for empty string; expected 1")
}
l := lines.lines[0]
if expected := fixed.Int26_6(12094); l.ascent != expected {
if expected := fixed.Int26_6(10463); l.ascent != expected {
t.Errorf("unexpected ascent for empty string: %v, expected %v", l.ascent, expected)
}
if expected := fixed.Int26_6(2700); l.descent != expected {
if expected := fixed.Int26_6(2336); l.descent != expected {
t.Errorf("unexpected descent for empty string: %v, expected %v", l.descent, expected)
}
}

func TestCJKOrNotString(t *testing.T) {
ppem := fixed.I(200)
ltrFace, _ := opentype.Parse(goregular.TTF)
shaper := testShaper(ltrFace)

for _, r := range [][]rune{
[]rune("Sa"),
[]rune("SayHi"),
[]rune("SayHi 您好"),
[]rune("✨ⷽℎ↞⋇ⱜ⪫⢡⽛⣦␆Ⱨⳏ⳯⒛⭣╎⌞⟻⢇┃➡⬎⩱⸇ⷎ⟅▤⼶⇺⩳⎏⤬⬞ⴈ⋠⿶⢒₍☟⽂ⶦ⫰⭢⌹∼▀⾯⧂❽⩏ⓖ⟅⤔⍇␋⽓ₑ⢳⠑❂⊪⢘⽨⃯▴ⷿ"),
} {
t.Run("ascent/descent should fit font size", func(t *testing.T) {
lines := shaper.LayoutRunes(Parameters{
PxPerEm: ppem,
MaxWidth: 2000,
Locale: english,
}, r)

l := lines.lines[0]

if expected := fixed.Int26_6(10463); l.ascent != expected {
t.Errorf("unexpected ascent for string: %v, expected %v", l.ascent, expected)
}
if expected := fixed.Int26_6(2336); l.descent != expected {
t.Errorf("unexpected descent for empty string: %v, expected %v", l.descent, expected)
}
})
}
}

func TestNoFaces(t *testing.T) {
ppem := fixed.I(200)
shaper := testShaper()
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