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text.go
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text.go
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package canvas
import (
"errors"
"image"
"image/draw"
"io/ioutil"
"github.com/golang/freetype"
"github.com/golang/freetype/truetype"
"golang.org/x/image/font"
"golang.org/x/image/math/fixed"
)
var fontRenderingContext = newFRContext()
// Font is a loaded font that can be passed to the
// SetFont method
type Font struct {
font *truetype.Font
}
var fonts = make(map[string]*Font)
var zeroes [alphaTexSize]byte
var textImage *image.Alpha
var defaultFont *Font
// LoadFont loads a font and returns the result. The font
// can be a file name or a byte slice in TTF format
func (cv *Canvas) LoadFont(src interface{}) (*Font, error) {
var f *Font
switch v := src.(type) {
case *truetype.Font:
f = &Font{font: v}
case string:
data, err := ioutil.ReadFile(v)
if err != nil {
return nil, err
}
font, err := freetype.ParseFont(data)
if err != nil {
return nil, err
}
f = &Font{font: font}
case []byte:
font, err := freetype.ParseFont(v)
if err != nil {
return nil, err
}
f = &Font{font: font}
default:
return nil, errors.New("Unsupported source type")
}
if defaultFont == nil {
defaultFont = f
}
return f, nil
}
// FillText draws the given string at the given coordinates
// using the currently set font and font height
func (cv *Canvas) FillText(str string, x, y float64) {
if cv.state.font == nil {
return
}
frc := fontRenderingContext
frc.setFont(cv.state.font.font)
frc.setFontSize(cv.state.fontSize)
fnt := cv.state.font.font
curX := x
var p fixed.Point26_6
prev, hasPrev := truetype.Index(0), false
strFrom, strTo := 0, len(str)
curInside := false
var textOffset image.Point
var strWidth, strMaxY int
for i, rn := range str {
idx := fnt.Index(rn)
if idx == 0 {
idx = fnt.Index(' ')
}
advance, bounds, err := frc.glyphMeasure(idx, p)
if err != nil {
continue
}
if hasPrev {
kern := fnt.Kern(frc.scale, prev, idx)
if frc.hinting != font.HintingNone {
kern = (kern + 32) &^ 63
}
curX += float64(kern) / 64
}
w, h := cv.b.Size()
fw, fh := float64(w), float64(h)
p0 := cv.tf(vec{float64(bounds.Min.X) + curX, float64(bounds.Min.Y) + y})
p1 := cv.tf(vec{float64(bounds.Min.X) + curX, float64(bounds.Max.Y) + y})
p2 := cv.tf(vec{float64(bounds.Max.X) + curX, float64(bounds.Max.Y) + y})
p3 := cv.tf(vec{float64(bounds.Max.X) + curX, float64(bounds.Min.Y) + y})
inside := (p0[0] >= 0 || p1[0] >= 0 || p2[0] >= 0 || p3[0] >= 0) &&
(p0[1] >= 0 || p1[1] >= 0 || p2[1] >= 0 || p3[1] >= 0) &&
(p0[0] < fw || p1[0] < fw || p2[0] < fw || p3[0] < fw) &&
(p0[1] < fh || p1[1] < fh || p2[1] < fh || p3[1] < fh)
if !curInside && inside {
curInside = true
strFrom = i
x = curX
} else if curInside && !inside {
strTo = i
break
}
if i == 0 {
textOffset.X = bounds.Min.X
}
if bounds.Min.Y < textOffset.Y {
textOffset.Y = bounds.Min.Y
}
if bounds.Max.Y > strMaxY {
strMaxY = bounds.Max.Y
}
p.X += advance
curX += float64(advance) / 64
}
strWidth = p.X.Ceil() - textOffset.X
strHeight := strMaxY - textOffset.Y
if strFrom == strTo || strWidth == 0 || strHeight == 0 {
return
}
if textImage == nil || textImage.Bounds().Dx() < strWidth || textImage.Bounds().Dy() < strHeight {
var size int
for size = 2; size < alphaTexSize; size *= 2 {
if size >= strWidth && size >= strHeight {
break
}
}
if size > alphaTexSize {
size = alphaTexSize
}
textImage = image.NewAlpha(image.Rect(0, 0, size, size))
}
curX = x
p = fixed.Point26_6{}
for y := 0; y < strHeight; y++ {
off := textImage.PixOffset(0, y)
line := textImage.Pix[off : off+strWidth]
for i := range line {
line[i] = 0
}
}
prev, hasPrev = truetype.Index(0), false
for _, rn := range str[strFrom:strTo] {
idx := fnt.Index(rn)
if idx == 0 {
prev = 0
hasPrev = false
continue
}
if hasPrev {
kern := fnt.Kern(frc.scale, prev, idx)
if frc.hinting != font.HintingNone {
kern = (kern + 32) &^ 63
}
curX += float64(kern) / 64
}
advance, mask, offset, err := frc.glyph(idx, p)
if err != nil {
prev = 0
hasPrev = false
continue
}
p.X += advance
draw.Draw(textImage, mask.Bounds().Add(offset).Sub(textOffset), mask, image.ZP, draw.Over)
curX += float64(advance) / 64
}
if cv.state.textAlign == Center {
x -= float64(strWidth) * 0.5
} else if cv.state.textAlign == Right || cv.state.textAlign == End {
x -= float64(strWidth)
}
var yOff float64
metrics := cv.state.fontMetrics
switch cv.state.textBaseline {
case Alphabetic:
yOff = 0
case Middle:
yOff = -float64(metrics.Descent)/64 + float64(metrics.Height)*0.5/64
case Top, Hanging:
yOff = -float64(metrics.Descent)/64 + float64(metrics.Height)/64
case Bottom, Ideographic:
yOff = -float64(metrics.Descent) / 64
}
var pts [4][2]float64
pts[0] = cv.tf(vec{float64(textOffset.X) + x, float64(textOffset.Y) + y + yOff})
pts[1] = cv.tf(vec{float64(textOffset.X) + x, float64(textOffset.Y+strHeight) + y + yOff})
pts[2] = cv.tf(vec{float64(textOffset.X+strWidth) + x, float64(textOffset.Y+strHeight) + y + yOff})
pts[3] = cv.tf(vec{float64(textOffset.X+strWidth) + x, float64(textOffset.Y) + y + yOff})
mask := textImage.SubImage(image.Rect(0, 0, strWidth, strHeight)).(*image.Alpha)
cv.drawShadow(pts[:], mask, false)
stl := cv.backendFillStyle(&cv.state.fill, 1)
cv.b.FillImageMask(&stl, mask, pts)
}
// StrokeText draws the given string at the given coordinates
// using the currently set font and font height and using the
// current stroke style
func (cv *Canvas) StrokeText(str string, x, y float64) {
if cv.state.font == nil {
return
}
frc := fontRenderingContext
frc.setFont(cv.state.font.font)
frc.setFontSize(float64(cv.state.fontSize))
fnt := cv.state.font.font
for _, rn := range str {
idx := fnt.Index(rn)
if idx == 0 {
idx = fnt.Index(' ')
}
advance, _, err := frc.glyphMeasure(idx, fixed.Point26_6{})
if err != nil {
continue
}
cv.strokeRune(rn, vec{x, y})
x += float64(advance) / 64
}
}
func (cv *Canvas) strokeRune(rn rune, pos vec) {
gb := &truetype.GlyphBuf{}
gb.Load(cv.state.font.font, fixed.Int26_6(cv.state.fontSize*64), cv.state.font.font.Index(rn), font.HintingNone)
prevPath := cv.path
defer func() {
cv.path = prevPath
}()
from := 0
for _, to := range gb.Ends {
ps := gb.Points[from:to]
start := fixed.Point26_6{
X: ps[0].X,
Y: ps[0].Y,
}
others := []truetype.Point(nil)
if ps[0].Flags&0x01 != 0 {
others = ps[1:]
} else {
last := fixed.Point26_6{
X: ps[len(ps)-1].X,
Y: ps[len(ps)-1].Y,
}
if ps[len(ps)-1].Flags&0x01 != 0 {
start = last
others = ps[:len(ps)-1]
} else {
start = fixed.Point26_6{
X: (start.X + last.X) / 2,
Y: (start.Y + last.Y) / 2,
}
others = ps
}
}
p0, on0 := gb.Points[from], false
cv.MoveTo(float64(p0.X)/64+pos[0], pos[1]-float64(p0.Y)/64)
for _, p := range others {
on := p.Flags&0x01 != 0
if on {
if on0 {
cv.LineTo(float64(p.X)/64+pos[0], pos[1]-float64(p.Y)/64)
} else {
cv.QuadraticCurveTo(float64(p0.X)/64+pos[0], pos[1]-float64(p0.Y)/64, float64(p.X)/64+pos[0], pos[1]-float64(p.Y)/64)
}
} else {
if on0 {
// No-op.
} else {
mid := fixed.Point26_6{
X: (p0.X + p.X) / 2,
Y: (p0.Y + p.Y) / 2,
}
cv.QuadraticCurveTo(float64(p0.X)/64+pos[0], pos[1]-float64(p0.Y)/64, float64(mid.X)/64+pos[0], pos[1]-float64(mid.Y)/64)
}
}
p0, on0 = p, on
}
if on0 {
cv.LineTo(float64(start.X)/64+pos[0], pos[1]-float64(start.Y)/64)
} else {
cv.QuadraticCurveTo(float64(p0.X)/64+pos[0], pos[1]-float64(p0.Y)/64, float64(start.X)/64+pos[0], pos[1]-float64(start.Y)/64)
}
cv.ClosePath()
cv.Stroke()
from = to
}
}
// TextMetrics is the result of a MeasureText call
type TextMetrics struct {
Width float64
ActualBoundingBoxAscent float64
ActualBoundingBoxDescent float64
}
// MeasureText measures the given string using the
// current font and font height
func (cv *Canvas) MeasureText(str string) TextMetrics {
if cv.state.font == nil {
return TextMetrics{}
}
frc := fontRenderingContext
frc.setFont(cv.state.font.font)
frc.setFontSize(float64(cv.state.fontSize))
fnt := cv.state.font.font
var p fixed.Point26_6
var x float64
var minY float64
var maxY float64
prev, hasPrev := truetype.Index(0), false
for _, rn := range str {
idx := fnt.Index(rn)
if idx == 0 {
prev = 0
hasPrev = false
continue
}
if hasPrev {
kern := fnt.Kern(frc.scale, prev, idx)
if frc.hinting != font.HintingNone {
kern = (kern + 32) &^ 63
}
x += float64(kern) / 64
}
advance, glyphBounds, err := frc.glyphMeasure(idx, p)
if err != nil {
prev = 0
hasPrev = false
continue
}
if glyphMinY := float64(glyphBounds.Min.Y); glyphMinY < minY {
minY = glyphMinY
}
if glyphMaxY := float64(glyphBounds.Max.Y); glyphMaxY > maxY {
maxY = glyphMaxY
}
x += float64(advance) / 64
p.X += advance
}
return TextMetrics{
Width: x,
ActualBoundingBoxAscent: -minY,
ActualBoundingBoxDescent: +maxY,
}
}