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-rw-r--r--Godeps/_workspace/src/code.google.com/p/freetype-go/freetype/raster/stroke.go466
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diff --git a/Godeps/_workspace/src/code.google.com/p/freetype-go/freetype/raster/stroke.go b/Godeps/_workspace/src/code.google.com/p/freetype-go/freetype/raster/stroke.go
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+++ b/Godeps/_workspace/src/code.google.com/p/freetype-go/freetype/raster/stroke.go
@@ -0,0 +1,466 @@
+// Copyright 2010 The Freetype-Go Authors. All rights reserved.
+// Use of this source code is governed by your choice of either the
+// FreeType License or the GNU General Public License version 2 (or
+// any later version), both of which can be found in the LICENSE file.
+
+package raster
+
+// Two points are considered practically equal if the square of the distance
+// between them is less than one quarter (i.e. 16384 / 65536 in Fix64).
+const epsilon = 16384
+
+// A Capper signifies how to begin or end a stroked path.
+type Capper interface {
+ // Cap adds a cap to p given a pivot point and the normal vector of a
+ // terminal segment. The normal's length is half of the stroke width.
+ Cap(p Adder, halfWidth Fix32, pivot, n1 Point)
+}
+
+// The CapperFunc type adapts an ordinary function to be a Capper.
+type CapperFunc func(Adder, Fix32, Point, Point)
+
+func (f CapperFunc) Cap(p Adder, halfWidth Fix32, pivot, n1 Point) {
+ f(p, halfWidth, pivot, n1)
+}
+
+// A Joiner signifies how to join interior nodes of a stroked path.
+type Joiner interface {
+ // Join adds a join to the two sides of a stroked path given a pivot
+ // point and the normal vectors of the trailing and leading segments.
+ // Both normals have length equal to half of the stroke width.
+ Join(lhs, rhs Adder, halfWidth Fix32, pivot, n0, n1 Point)
+}
+
+// The JoinerFunc type adapts an ordinary function to be a Joiner.
+type JoinerFunc func(lhs, rhs Adder, halfWidth Fix32, pivot, n0, n1 Point)
+
+func (f JoinerFunc) Join(lhs, rhs Adder, halfWidth Fix32, pivot, n0, n1 Point) {
+ f(lhs, rhs, halfWidth, pivot, n0, n1)
+}
+
+// RoundCapper adds round caps to a stroked path.
+var RoundCapper Capper = CapperFunc(roundCapper)
+
+func roundCapper(p Adder, halfWidth Fix32, pivot, n1 Point) {
+ // The cubic Bézier approximation to a circle involves the magic number
+ // (√2 - 1) * 4/3, which is approximately 141/256.
+ const k = 141
+ e := n1.Rot90CCW()
+ side := pivot.Add(e)
+ start, end := pivot.Sub(n1), pivot.Add(n1)
+ d, e := n1.Mul(k), e.Mul(k)
+ p.Add3(start.Add(e), side.Sub(d), side)
+ p.Add3(side.Add(d), end.Add(e), end)
+}
+
+// ButtCapper adds butt caps to a stroked path.
+var ButtCapper Capper = CapperFunc(buttCapper)
+
+func buttCapper(p Adder, halfWidth Fix32, pivot, n1 Point) {
+ p.Add1(pivot.Add(n1))
+}
+
+// SquareCapper adds square caps to a stroked path.
+var SquareCapper Capper = CapperFunc(squareCapper)
+
+func squareCapper(p Adder, halfWidth Fix32, pivot, n1 Point) {
+ e := n1.Rot90CCW()
+ side := pivot.Add(e)
+ p.Add1(side.Sub(n1))
+ p.Add1(side.Add(n1))
+ p.Add1(pivot.Add(n1))
+}
+
+// RoundJoiner adds round joins to a stroked path.
+var RoundJoiner Joiner = JoinerFunc(roundJoiner)
+
+func roundJoiner(lhs, rhs Adder, haflWidth Fix32, pivot, n0, n1 Point) {
+ dot := n0.Rot90CW().Dot(n1)
+ if dot >= 0 {
+ addArc(lhs, pivot, n0, n1)
+ rhs.Add1(pivot.Sub(n1))
+ } else {
+ lhs.Add1(pivot.Add(n1))
+ addArc(rhs, pivot, n0.Neg(), n1.Neg())
+ }
+}
+
+// BevelJoiner adds bevel joins to a stroked path.
+var BevelJoiner Joiner = JoinerFunc(bevelJoiner)
+
+func bevelJoiner(lhs, rhs Adder, haflWidth Fix32, pivot, n0, n1 Point) {
+ lhs.Add1(pivot.Add(n1))
+ rhs.Add1(pivot.Sub(n1))
+}
+
+// addArc adds a circular arc from pivot+n0 to pivot+n1 to p. The shorter of
+// the two possible arcs is taken, i.e. the one spanning <= 180 degrees.
+// The two vectors n0 and n1 must be of equal length.
+func addArc(p Adder, pivot, n0, n1 Point) {
+ // r2 is the square of the length of n0.
+ r2 := n0.Dot(n0)
+ if r2 < epsilon {
+ // The arc radius is so small that we collapse to a straight line.
+ p.Add1(pivot.Add(n1))
+ return
+ }
+ // We approximate the arc by 0, 1, 2 or 3 45-degree quadratic segments plus
+ // a final quadratic segment from s to n1. Each 45-degree segment has control
+ // points {1, 0}, {1, tan(π/8)} and {1/√2, 1/√2} suitably scaled, rotated and
+ // translated. tan(π/8) is approximately 106/256.
+ const tpo8 = 106
+ var s Point
+ // We determine which octant the angle between n0 and n1 is in via three dot products.
+ // m0, m1 and m2 are n0 rotated clockwise by 45, 90 and 135 degrees.
+ m0 := n0.Rot45CW()
+ m1 := n0.Rot90CW()
+ m2 := m0.Rot90CW()
+ if m1.Dot(n1) >= 0 {
+ if n0.Dot(n1) >= 0 {
+ if m2.Dot(n1) <= 0 {
+ // n1 is between 0 and 45 degrees clockwise of n0.
+ s = n0
+ } else {
+ // n1 is between 45 and 90 degrees clockwise of n0.
+ p.Add2(pivot.Add(n0).Add(m1.Mul(tpo8)), pivot.Add(m0))
+ s = m0
+ }
+ } else {
+ pm1, n0t := pivot.Add(m1), n0.Mul(tpo8)
+ p.Add2(pivot.Add(n0).Add(m1.Mul(tpo8)), pivot.Add(m0))
+ p.Add2(pm1.Add(n0t), pm1)
+ if m0.Dot(n1) >= 0 {
+ // n1 is between 90 and 135 degrees clockwise of n0.
+ s = m1
+ } else {
+ // n1 is between 135 and 180 degrees clockwise of n0.
+ p.Add2(pm1.Sub(n0t), pivot.Add(m2))
+ s = m2
+ }
+ }
+ } else {
+ if n0.Dot(n1) >= 0 {
+ if m0.Dot(n1) >= 0 {
+ // n1 is between 0 and 45 degrees counter-clockwise of n0.
+ s = n0
+ } else {
+ // n1 is between 45 and 90 degrees counter-clockwise of n0.
+ p.Add2(pivot.Add(n0).Sub(m1.Mul(tpo8)), pivot.Sub(m2))
+ s = m2.Neg()
+ }
+ } else {
+ pm1, n0t := pivot.Sub(m1), n0.Mul(tpo8)
+ p.Add2(pivot.Add(n0).Sub(m1.Mul(tpo8)), pivot.Sub(m2))
+ p.Add2(pm1.Add(n0t), pm1)
+ if m2.Dot(n1) <= 0 {
+ // n1 is between 90 and 135 degrees counter-clockwise of n0.
+ s = m1.Neg()
+ } else {
+ // n1 is between 135 and 180 degrees counter-clockwise of n0.
+ p.Add2(pm1.Sub(n0t), pivot.Sub(m0))
+ s = m0.Neg()
+ }
+ }
+ }
+ // The final quadratic segment has two endpoints s and n1 and the middle
+ // control point is a multiple of s.Add(n1), i.e. it is on the angle bisector
+ // of those two points. The multiple ranges between 128/256 and 150/256 as
+ // the angle between s and n1 ranges between 0 and 45 degrees.
+ // When the angle is 0 degrees (i.e. s and n1 are coincident) then s.Add(n1)
+ // is twice s and so the middle control point of the degenerate quadratic
+ // segment should be half s.Add(n1), and half = 128/256.
+ // When the angle is 45 degrees then 150/256 is the ratio of the lengths of
+ // the two vectors {1, tan(π/8)} and {1 + 1/√2, 1/√2}.
+ // d is the normalized dot product between s and n1. Since the angle ranges
+ // between 0 and 45 degrees then d ranges between 256/256 and 181/256.
+ d := 256 * s.Dot(n1) / r2
+ multiple := Fix32(150 - 22*(d-181)/(256-181))
+ p.Add2(pivot.Add(s.Add(n1).Mul(multiple)), pivot.Add(n1))
+}
+
+// midpoint returns the midpoint of two Points.
+func midpoint(a, b Point) Point {
+ return Point{(a.X + b.X) / 2, (a.Y + b.Y) / 2}
+}
+
+// angleGreaterThan45 returns whether the angle between two vectors is more
+// than 45 degrees.
+func angleGreaterThan45(v0, v1 Point) bool {
+ v := v0.Rot45CCW()
+ return v.Dot(v1) < 0 || v.Rot90CW().Dot(v1) < 0
+}
+
+// interpolate returns the point (1-t)*a + t*b.
+func interpolate(a, b Point, t Fix64) Point {
+ s := 65536 - t
+ x := s*Fix64(a.X) + t*Fix64(b.X)
+ y := s*Fix64(a.Y) + t*Fix64(b.Y)
+ return Point{Fix32(x >> 16), Fix32(y >> 16)}
+}
+
+// curviest2 returns the value of t for which the quadratic parametric curve
+// (1-t)²*a + 2*t*(1-t).b + t²*c has maximum curvature.
+//
+// The curvature of the parametric curve f(t) = (x(t), y(t)) is
+// |x′y″-y′x″| / (x′²+y′²)^(3/2).
+//
+// Let d = b-a and e = c-2*b+a, so that f′(t) = 2*d+2*e*t and f″(t) = 2*e.
+// The curvature's numerator is (2*dx+2*ex*t)*(2*ey)-(2*dy+2*ey*t)*(2*ex),
+// which simplifies to 4*dx*ey-4*dy*ex, which is constant with respect to t.
+//
+// Thus, curvature is extreme where the denominator is extreme, i.e. where
+// (x′²+y′²) is extreme. The first order condition is that
+// 2*x′*x″+2*y′*y″ = 0, or (dx+ex*t)*ex + (dy+ey*t)*ey = 0.
+// Solving for t gives t = -(dx*ex+dy*ey) / (ex*ex+ey*ey).
+func curviest2(a, b, c Point) Fix64 {
+ dx := int64(b.X - a.X)
+ dy := int64(b.Y - a.Y)
+ ex := int64(c.X - 2*b.X + a.X)
+ ey := int64(c.Y - 2*b.Y + a.Y)
+ if ex == 0 && ey == 0 {
+ return 32768
+ }
+ return Fix64(-65536 * (dx*ex + dy*ey) / (ex*ex + ey*ey))
+}
+
+// A stroker holds state for stroking a path.
+type stroker struct {
+ // p is the destination that records the stroked path.
+ p Adder
+ // u is the half-width of the stroke.
+ u Fix32
+ // cr and jr specify how to end and connect path segments.
+ cr Capper
+ jr Joiner
+ // r is the reverse path. Stroking a path involves constructing two
+ // parallel paths 2*u apart. The first path is added immediately to p,
+ // the second path is accumulated in r and eventually added in reverse.
+ r Path
+ // a is the most recent segment point. anorm is the segment normal of
+ // length u at that point.
+ a, anorm Point
+}
+
+// addNonCurvy2 adds a quadratic segment to the stroker, where the segment
+// defined by (k.a, b, c) achieves maximum curvature at either k.a or c.
+func (k *stroker) addNonCurvy2(b, c Point) {
+ // We repeatedly divide the segment at its middle until it is straight
+ // enough to approximate the stroke by just translating the control points.
+ // ds and ps are stacks of depths and points. t is the top of the stack.
+ const maxDepth = 5
+ var (
+ ds [maxDepth + 1]int
+ ps [2*maxDepth + 3]Point
+ t int
+ )
+ // Initially the ps stack has one quadratic segment of depth zero.
+ ds[0] = 0
+ ps[2] = k.a
+ ps[1] = b
+ ps[0] = c
+ anorm := k.anorm
+ var cnorm Point
+
+ for {
+ depth := ds[t]
+ a := ps[2*t+2]
+ b := ps[2*t+1]
+ c := ps[2*t+0]
+ ab := b.Sub(a)
+ bc := c.Sub(b)
+ abIsSmall := ab.Dot(ab) < Fix64(1<<16)
+ bcIsSmall := bc.Dot(bc) < Fix64(1<<16)
+ if abIsSmall && bcIsSmall {
+ // Approximate the segment by a circular arc.
+ cnorm = bc.Norm(k.u).Rot90CCW()
+ mac := midpoint(a, c)
+ addArc(k.p, mac, anorm, cnorm)
+ addArc(&k.r, mac, anorm.Neg(), cnorm.Neg())
+ } else if depth < maxDepth && angleGreaterThan45(ab, bc) {
+ // Divide the segment in two and push both halves on the stack.
+ mab := midpoint(a, b)
+ mbc := midpoint(b, c)
+ t++
+ ds[t+0] = depth + 1
+ ds[t-1] = depth + 1
+ ps[2*t+2] = a
+ ps[2*t+1] = mab
+ ps[2*t+0] = midpoint(mab, mbc)
+ ps[2*t-1] = mbc
+ continue
+ } else {
+ // Translate the control points.
+ bnorm := c.Sub(a).Norm(k.u).Rot90CCW()
+ cnorm = bc.Norm(k.u).Rot90CCW()
+ k.p.Add2(b.Add(bnorm), c.Add(cnorm))
+ k.r.Add2(b.Sub(bnorm), c.Sub(cnorm))
+ }
+ if t == 0 {
+ k.a, k.anorm = c, cnorm
+ return
+ }
+ t--
+ anorm = cnorm
+ }
+ panic("unreachable")
+}
+
+// Add1 adds a linear segment to the stroker.
+func (k *stroker) Add1(b Point) {
+ bnorm := b.Sub(k.a).Norm(k.u).Rot90CCW()
+ if len(k.r) == 0 {
+ k.p.Start(k.a.Add(bnorm))
+ k.r.Start(k.a.Sub(bnorm))
+ } else {
+ k.jr.Join(k.p, &k.r, k.u, k.a, k.anorm, bnorm)
+ }
+ k.p.Add1(b.Add(bnorm))
+ k.r.Add1(b.Sub(bnorm))
+ k.a, k.anorm = b, bnorm
+}
+
+// Add2 adds a quadratic segment to the stroker.
+func (k *stroker) Add2(b, c Point) {
+ ab := b.Sub(k.a)
+ bc := c.Sub(b)
+ abnorm := ab.Norm(k.u).Rot90CCW()
+ if len(k.r) == 0 {
+ k.p.Start(k.a.Add(abnorm))
+ k.r.Start(k.a.Sub(abnorm))
+ } else {
+ k.jr.Join(k.p, &k.r, k.u, k.a, k.anorm, abnorm)
+ }
+
+ // Approximate nearly-degenerate quadratics by linear segments.
+ abIsSmall := ab.Dot(ab) < epsilon
+ bcIsSmall := bc.Dot(bc) < epsilon
+ if abIsSmall || bcIsSmall {
+ acnorm := c.Sub(k.a).Norm(k.u).Rot90CCW()
+ k.p.Add1(c.Add(acnorm))
+ k.r.Add1(c.Sub(acnorm))
+ k.a, k.anorm = c, acnorm
+ return
+ }
+
+ // The quadratic segment (k.a, b, c) has a point of maximum curvature.
+ // If this occurs at an end point, we process the segment as a whole.
+ t := curviest2(k.a, b, c)
+ if t <= 0 || t >= 65536 {
+ k.addNonCurvy2(b, c)
+ return
+ }
+
+ // Otherwise, we perform a de Casteljau decomposition at the point of
+ // maximum curvature and process the two straighter parts.
+ mab := interpolate(k.a, b, t)
+ mbc := interpolate(b, c, t)
+ mabc := interpolate(mab, mbc, t)
+
+ // If the vectors ab and bc are close to being in opposite directions,
+ // then the decomposition can become unstable, so we approximate the
+ // quadratic segment by two linear segments joined by an arc.
+ bcnorm := bc.Norm(k.u).Rot90CCW()
+ if abnorm.Dot(bcnorm) < -Fix64(k.u)*Fix64(k.u)*2047/2048 {
+ pArc := abnorm.Dot(bc) < 0
+
+ k.p.Add1(mabc.Add(abnorm))
+ if pArc {
+ z := abnorm.Rot90CW()
+ addArc(k.p, mabc, abnorm, z)
+ addArc(k.p, mabc, z, bcnorm)
+ }
+ k.p.Add1(mabc.Add(bcnorm))
+ k.p.Add1(c.Add(bcnorm))
+
+ k.r.Add1(mabc.Sub(abnorm))
+ if !pArc {
+ z := abnorm.Rot90CW()
+ addArc(&k.r, mabc, abnorm.Neg(), z)
+ addArc(&k.r, mabc, z, bcnorm.Neg())
+ }
+ k.r.Add1(mabc.Sub(bcnorm))
+ k.r.Add1(c.Sub(bcnorm))
+
+ k.a, k.anorm = c, bcnorm
+ return
+ }
+
+ // Process the decomposed parts.
+ k.addNonCurvy2(mab, mabc)
+ k.addNonCurvy2(mbc, c)
+}
+
+// Add3 adds a cubic segment to the stroker.
+func (k *stroker) Add3(b, c, d Point) {
+ panic("freetype/raster: stroke unimplemented for cubic segments")
+}
+
+// stroke adds the stroked Path q to p, where q consists of exactly one curve.
+func (k *stroker) stroke(q Path) {
+ // Stroking is implemented by deriving two paths each k.u apart from q.
+ // The left-hand-side path is added immediately to k.p; the right-hand-side
+ // path is accumulated in k.r. Once we've finished adding the LHS to k.p,
+ // we add the RHS in reverse order.
+ k.r = make(Path, 0, len(q))
+ k.a = Point{q[1], q[2]}
+ for i := 4; i < len(q); {
+ switch q[i] {
+ case 1:
+ k.Add1(Point{q[i+1], q[i+2]})
+ i += 4
+ case 2:
+ k.Add2(Point{q[i+1], q[i+2]}, Point{q[i+3], q[i+4]})
+ i += 6
+ case 3:
+ k.Add3(Point{q[i+1], q[i+2]}, Point{q[i+3], q[i+4]}, Point{q[i+5], q[i+6]})
+ i += 8
+ default:
+ panic("freetype/raster: bad path")
+ }
+ }
+ if len(k.r) == 0 {
+ return
+ }
+ // TODO(nigeltao): if q is a closed curve then we should join the first and
+ // last segments instead of capping them.
+ k.cr.Cap(k.p, k.u, q.lastPoint(), k.anorm.Neg())
+ addPathReversed(k.p, k.r)
+ pivot := q.firstPoint()
+ k.cr.Cap(k.p, k.u, pivot, pivot.Sub(Point{k.r[1], k.r[2]}))
+}
+
+// Stroke adds q stroked with the given width to p. The result is typically
+// self-intersecting and should be rasterized with UseNonZeroWinding.
+// cr and jr may be nil, which defaults to a RoundCapper or RoundJoiner.
+func Stroke(p Adder, q Path, width Fix32, cr Capper, jr Joiner) {
+ if len(q) == 0 {
+ return
+ }
+ if cr == nil {
+ cr = RoundCapper
+ }
+ if jr == nil {
+ jr = RoundJoiner
+ }
+ if q[0] != 0 {
+ panic("freetype/raster: bad path")
+ }
+ s := stroker{p: p, u: width / 2, cr: cr, jr: jr}
+ i := 0
+ for j := 4; j < len(q); {
+ switch q[j] {
+ case 0:
+ s.stroke(q[i:j])
+ i, j = j, j+4
+ case 1:
+ j += 4
+ case 2:
+ j += 6
+ case 3:
+ j += 8
+ default:
+ panic("freetype/raster: bad path")
+ }
+ }
+ s.stroke(q[i:])
+}
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