83 lines
2.1 KiB
Go
83 lines
2.1 KiB
Go
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package draw2dgl
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import (
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"github.com/golang/freetype/truetype"
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"github.com/llgcode/draw2d"
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"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) {
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if len(ps) == 0 {
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return
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}
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startX, startY := pointToF64Point(ps[0])
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path.MoveTo(startX+dx, startY+dy)
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q0X, q0Y, on0 := startX, startY, true
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for _, p := range ps[1:] {
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qX, qY := pointToF64Point(p)
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on := p.Flags&0x01 != 0
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if on {
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if on0 {
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path.LineTo(qX+dx, qY+dy)
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} else {
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path.QuadCurveTo(q0X+dx, q0Y+dy, qX+dx, qY+dy)
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}
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} else {
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if on0 {
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// No-op.
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} else {
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midX := (q0X + qX) / 2
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midY := (q0Y + qY) / 2
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path.QuadCurveTo(q0X+dx, q0Y+dy, midX+dx, midY+dy)
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}
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}
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q0X, q0Y, on0 = qX, qY, on
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}
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// Close the curve.
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if on0 {
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path.LineTo(startX+dx, startY+dy)
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} else {
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path.QuadCurveTo(q0X+dx, q0Y+dy, startX+dx, startY+dy)
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}
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}
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func pointToF64Point(p truetype.Point) (x, y float64) {
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return fUnitsToFloat64(p.X), -fUnitsToFloat64(p.Y)
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}
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func fUnitsToFloat64(x fixed.Int26_6) float64 {
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scaled := x << 2
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return float64(scaled/256) + float64(scaled%256)/256.0
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}
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// FontExtents contains font metric information.
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type FontExtents struct {
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// Ascent is the distance that the text
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// extends above the baseline.
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Ascent float64
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// Descent is the distance that the text
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// extends below the baseline. The descent
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// is given as a negative value.
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Descent float64
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// Height is the distance from the lowest
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// descending point to the highest ascending
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// point.
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Height float64
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}
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// 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 {
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bounds := font.Bounds(fixed.Int26_6(font.FUnitsPerEm()))
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scale := size / float64(font.FUnitsPerEm())
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return FontExtents{
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Ascent: float64(bounds.Max.Y) * scale,
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Descent: float64(bounds.Min.Y) * scale,
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Height: float64(bounds.Max.Y-bounds.Min.Y) * scale,
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}
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}
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