draw2d/draw2dimg/text.go

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package draw2dimg
import (
"github.com/golang/freetype/truetype"
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"github.com/llgcode/draw2d"
"golang.org/x/image/math/fixed"
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)
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// DrawContour draws the given closed contour at the given sub-pixel offset.
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func DrawContour(path draw2d.PathBuilder, ps []truetype.Point, dx, dy float64) {
if len(ps) == 0 {
return
}
startX, startY := pointToF64Point(ps[0])
path.MoveTo(startX+dx, startY+dy)
q0X, q0Y, on0 := startX, startY, true
for _, p := range ps[1:] {
qX, qY := pointToF64Point(p)
on := p.Flags&0x01 != 0
if on {
if on0 {
path.LineTo(qX+dx, qY+dy)
} else {
path.QuadCurveTo(q0X+dx, q0Y+dy, qX+dx, qY+dy)
}
} else {
if on0 {
// No-op.
} else {
midX := (q0X + qX) / 2
midY := (q0Y + qY) / 2
path.QuadCurveTo(q0X+dx, q0Y+dy, midX+dx, midY+dy)
}
}
q0X, q0Y, on0 = qX, qY, on
}
// Close the curve.
if on0 {
path.LineTo(startX+dx, startY+dy)
} else {
path.QuadCurveTo(q0X+dx, q0Y+dy, startX+dx, startY+dy)
}
}
func pointToF64Point(p truetype.Point) (x, y float64) {
return fUnitsToFloat64(p.X), -fUnitsToFloat64(p.Y)
}
func fUnitsToFloat64(x fixed.Int26_6) float64 {
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scaled := x << 2
return float64(scaled/256) + float64(scaled%256)/256.0
}
// FontExtents contains font metric information.
type FontExtents struct {
// Ascent is the distance that the text
// extends above the baseline.
Ascent float64
// Descent is the distance that the text
// extends below the baseline. The descent
// is given as a negative value.
Descent float64
// Height is the distance from the lowest
// descending point to the highest ascending
// point.
Height float64
}
// Extents returns the FontExtents for a font.
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// TODO needs to read this https://developer.apple.com/fonts/TrueType-Reference-Manual/RM02/Chap2.html#intro
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func Extents(font *truetype.Font, size float64) FontExtents {
bounds := font.Bounds(fixed.Int26_6(font.FUnitsPerEm()))
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scale := size / float64(font.FUnitsPerEm())
return FontExtents{
Ascent: float64(bounds.Max.Y) * scale,
Descent: float64(bounds.Min.Y) * scale,
Height: float64(bounds.Max.Y-bounds.Min.Y) * scale,
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}
}