1package draw2dimg
2
3import (
4	"github.com/golang/freetype/truetype"
5	"github.com/llgcode/draw2d"
6
7	"golang.org/x/image/math/fixed"
8)
9
10// DrawContour draws the given closed contour at the given sub-pixel offset.
11func DrawContour(path draw2d.PathBuilder, ps []truetype.Point, dx, dy float64) {
12	if len(ps) == 0 {
13		return
14	}
15	startX, startY := pointToF64Point(ps[0])
16	path.MoveTo(startX+dx, startY+dy)
17	q0X, q0Y, on0 := startX, startY, true
18	for _, p := range ps[1:] {
19		qX, qY := pointToF64Point(p)
20		on := p.Flags&0x01 != 0
21		if on {
22			if on0 {
23				path.LineTo(qX+dx, qY+dy)
24			} else {
25				path.QuadCurveTo(q0X+dx, q0Y+dy, qX+dx, qY+dy)
26			}
27		} else {
28			if on0 {
29				// No-op.
30			} else {
31				midX := (q0X + qX) / 2
32				midY := (q0Y + qY) / 2
33				path.QuadCurveTo(q0X+dx, q0Y+dy, midX+dx, midY+dy)
34			}
35		}
36		q0X, q0Y, on0 = qX, qY, on
37	}
38	// Close the curve.
39	if on0 {
40		path.LineTo(startX+dx, startY+dy)
41	} else {
42		path.QuadCurveTo(q0X+dx, q0Y+dy, startX+dx, startY+dy)
43	}
44}
45
46func pointToF64Point(p truetype.Point) (x, y float64) {
47	return fUnitsToFloat64(p.X), -fUnitsToFloat64(p.Y)
48}
49
50func fUnitsToFloat64(x fixed.Int26_6) float64 {
51	scaled := x << 2
52	return float64(scaled/256) + float64(scaled%256)/256.0
53}
54
55// FontExtents contains font metric information.
56type FontExtents struct {
57	// Ascent is the distance that the text
58	// extends above the baseline.
59	Ascent float64
60
61	// Descent is the distance that the text
62	// extends below the baseline.  The descent
63	// is given as a negative value.
64	Descent float64
65
66	// Height is the distance from the lowest
67	// descending point to the highest ascending
68	// point.
69	Height float64
70}
71
72// Extents returns the FontExtents for a font.
73// TODO needs to read this https://developer.apple.com/fonts/TrueType-Reference-Manual/RM02/Chap2.html#intro
74func Extents(font *truetype.Font, size float64) FontExtents {
75	bounds := font.Bounds(fixed.Int26_6(font.FUnitsPerEm()))
76	scale := size / float64(font.FUnitsPerEm())
77	return FontExtents{
78		Ascent:  float64(bounds.Max.Y) * scale,
79		Descent: float64(bounds.Min.Y) * scale,
80		Height:  float64(bounds.Max.Y-bounds.Min.Y) * scale,
81	}
82}
83