// DrawString draws s at p and returns p advanced by the text extent. The text
// is placed so that the left edge of the em square of the first character of s
// and the baseline intersect at p. The majority of the affected pixels will be
// above and to the right of the point, but some may be below or to the left.
// For example, drawing a string that starts with a 'J' in an italic font may
// affect pixels below and left of the point.
// p is a raster.Point and can therefore represent sub-pixel positions.
func (c *Context) DrawString(s string, p raster.Point) (raster.Point, error) {
if c.font == nil {
return raster.Point{}, errors.New("freetype: DrawText called with a nil font")
}
prev, hasPrev := truetype.Index(0), false
for _, rune := range s {
index := c.font.Index(rune)
if hasPrev {
kern := raster.Fix32(c.font.Kerning(c.scale, prev, index)) << 2
if c.hinting != NoHinting {
kern = (kern + 128) &^ 255
}
p.X += kern
}
advanceWidth, mask, offset, err := c.glyph(index, p)
if err != nil {
return raster.Point{}, err
}
p.X += advanceWidth
glyphRect := mask.Bounds().Add(offset)
dr := c.clip.Intersect(glyphRect)
if !dr.Empty() {
mp := image.Point{0, dr.Min.Y - glyphRect.Min.Y}
draw.DrawMask(c.dst, dr, c.src, image.ZP, mask, mp, draw.Over)
}
prev, hasPrev = index, true
}
return p, nil
}
// rasterize returns the advance width, glyph mask and integer-pixel offset
// to render the given glyph at the given sub-pixel offsets.
// The 24.8 fixed point arguments fx and fy must be in the range [0, 1).
func (c *Context) rasterize(glyph truetype.Index, fx, fy raster.Fix32) (
raster.Fix32, *image.Alpha, image.Point, error) {
if err := c.glyphBuf.Load(c.font, c.scale, glyph, truetype.Hinting(c.hinting)); err != nil {
return 0, nil, image.Point{}, err
}
// Calculate the integer-pixel bounds for the glyph.
xmin := int(fx+raster.Fix32(c.glyphBuf.B.XMin<<2)) >> 8
ymin := int(fy-raster.Fix32(c.glyphBuf.B.YMax<<2)) >> 8
xmax := int(fx+raster.Fix32(c.glyphBuf.B.XMax<<2)+0xff) >> 8
ymax := int(fy-raster.Fix32(c.glyphBuf.B.YMin<<2)+0xff) >> 8
if xmin > xmax || ymin > ymax {
return 0, nil, image.Point{}, errors.New("freetype: negative sized glyph")
}
// A TrueType's glyph's nodes can have negative co-ordinates, but the
// rasterizer clips anything left of x=0 or above y=0. xmin and ymin
// are the pixel offsets, based on the font's FUnit metrics, that let
// a negative co-ordinate in TrueType space be non-negative in
// rasterizer space. xmin and ymin are typically <= 0.
fx += raster.Fix32(-xmin << 8)
fy += raster.Fix32(-ymin << 8)
// Rasterize the glyph's vectors.
c.r.Clear()
e0 := 0
for _, e1 := range c.glyphBuf.End {
c.drawContour(c.glyphBuf.Point[e0:e1], fx, fy)
e0 = e1
}
a := image.NewAlpha(image.Rect(0, 0, xmax-xmin, ymax-ymin))
c.r.Rasterize(raster.NewAlphaSrcPainter(a))
return raster.Fix32(c.glyphBuf.AdvanceWidth << 2), a, image.Point{xmin, ymin}, nil
}
// drawContour draws the given closed contour with the given offset.
func (c *Context) drawContour(ps []truetype.Point, dx, dy raster.Fix32) {
if len(ps) == 0 {
return
}
// The low bit of each point's Flags value is whether the point is on the
// curve. Truetype fonts only have quadratic Bézier curves, not cubics.
// Thus, two consecutive off-curve points imply an on-curve point in the
// middle of those two.
//
// See http://chanae.walon.org/pub/ttf/ttf_glyphs.htm for more details.
// ps[0] is a truetype.Point measured in FUnits and positive Y going
// upwards. start is the same thing measured in fixed point units and
// positive Y going downwards, and offset by (dx, dy).
start := raster.Point{
X: dx + raster.Fix32(ps[0].X<<2),
Y: dy - raster.Fix32(ps[0].Y<<2),
}
others := []truetype.Point(nil)
if ps[0].Flags&0x01 != 0 {
others = ps[1:]
} else {
last := raster.Point{
X: dx + raster.Fix32(ps[len(ps)-1].X<<2),
Y: dy - raster.Fix32(ps[len(ps)-1].Y<<2),
}
if ps[len(ps)-1].Flags&0x01 != 0 {
start = last
others = ps[:len(ps)-1]
} else {
start = raster.Point{
X: (start.X + last.X) / 2,
Y: (start.Y + last.Y) / 2,
}
others = ps
}
}
c.r.Start(start)
q0, on0 := start, true
for _, p := range others {
q := raster.Point{
X: dx + raster.Fix32(p.X<<2),
Y: dy - raster.Fix32(p.Y<<2),
}
on := p.Flags&0x01 != 0
if on {
if on0 {
c.r.Add1(q)
} else {
c.r.Add2(q0, q)
}
} else {
if on0 {
// No-op.
} else {
mid := raster.Point{
X: (q0.X + q.X) / 2,
Y: (q0.Y + q.Y) / 2,
}
c.r.Add2(q0, mid)
}
}
q0, on0 = q, on
}
// Close the curve.
if on0 {
c.r.Add1(start)
} else {
c.r.Add2(q0, start)
}
}
// PointToFix32 converts the given number of points (as in ``a 12 point font'')
// into fixed point units.
func (c *Context) PointToFix32(x float64) raster.Fix32 {
return raster.Fix32(x * float64(c.dpi) * (256.0 / 72.0))
}
// Pt converts from a co-ordinate pair measured in pixels to a raster.Point
// co-ordinate pair measured in raster.Fix32 units.
func Pt(x, y int) raster.Point {
return raster.Point{
X: raster.Fix32(x << 8),
Y: raster.Fix32(y << 8),
}
}