text.go

// NOTE that this is identical copy of draw2dgl/text.go and draw2dimg/text.go
package draw2dsvg

import (
	"github.com/golang/freetype/truetype"
	"github.com/llgcode/draw2d"
	"golang.org/x/image/math/fixed"
)

// DrawContour draws the given closed contour at the given sub-pixel offset.
func DrawContour(path draw2d.PathBuilder, ps []truetype.Point, dx, dy float64) {
	if len(ps) == 0 {
		return
	}
	startX, startY := pointToF64Point(ps[0])
	var others []truetype.Point
	if ps[0].Flags&0x01 != 0 {
		others = ps[1:]
	} else {
		lastX, lastY := pointToF64Point(ps[len(ps)-1])
		if ps[len(ps)-1].Flags&0x01 != 0 {
			startX, startY = lastX, lastY
			others = ps[:len(ps)-1]
		} else {
			startX = (startX + lastX) / 2
			startY = (startY + lastY) / 2
			others = ps
		}
	}
	path.MoveTo(startX+dx, startY+dy)
	q0X, q0Y, on0 := startX, startY, true
	for _, p := range others {
		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 {
	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.
// TODO needs to read this https://developer.apple.com/fonts/TrueType-Reference-Manual/RM02/Chap2.html#intro
func Extents(font *truetype.Font, size float64) FontExtents {
	bounds := font.Bounds(fixed.Int26_6(font.FUnitsPerEm()))
	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,
	}
}