vector: add a fixed point math implementation.

name                      old time/op  new time/op  delta

GlyphAlpha16Over-8        4.48µs ± 1%  3.56µs ± 0%  -20.70%   (p=0.000 n=9+10)
GlyphAlpha16Src-8         4.17µs ± 0%  3.38µs ± 1%  -19.09%  (p=0.000 n=10+10)
GlyphAlpha32Over-8        9.03µs ± 0%  6.74µs ± 0%  -25.33%   (p=0.000 n=9+10)
GlyphAlpha32Src-8         7.46µs ± 1%  5.98µs ± 0%  -19.80%   (p=0.000 n=10+9)
GlyphAlpha64Over-8        21.3µs ± 0%  16.4µs ± 0%  -22.84%  (p=0.000 n=10+10)
GlyphAlpha64Src-8         16.2µs ± 1%  13.1µs ± 0%  -19.33%  (p=0.000 n=10+10)
GlyphAlpha128Over-8       59.8µs ± 0%  47.2µs ± 0%  -21.11%    (p=0.000 n=9+9)
GlyphAlpha128Src-8        41.3µs ± 1%  33.0µs ± 0%  -20.26%   (p=0.000 n=9+10)
GlyphAlpha256Over-8        197µs ± 0%   158µs ± 0%  -19.44%   (p=0.000 n=9+10)
GlyphAlpha256Src-8         124µs ± 0%    98µs ± 0%  -21.17%    (p=0.000 n=9+9)

GlyphAlphaLoose16Over-8   4.73µs ± 0%  3.97µs ± 1%  -16.06%  (p=0.000 n=10+10)
GlyphAlphaLoose16Src-8    4.41µs ± 0%  3.64µs ± 1%  -17.50%  (p=0.000 n=10+10)
GlyphAlphaLoose32Over-8   9.62µs ± 0%  8.47µs ± 0%  -11.95%  (p=0.000 n=10+10)
GlyphAlphaLoose32Src-8    8.25µs ± 0%  7.19µs ± 0%  -12.88%    (p=0.000 n=9+9)
GlyphAlphaLoose64Over-8   25.6µs ± 0%  22.2µs ± 0%  -13.01%    (p=0.000 n=9+9)
GlyphAlphaLoose64Src-8    20.2µs ± 0%  17.2µs ± 1%  -14.98%  (p=0.000 n=10+10)
GlyphAlphaLoose128Over-8  83.4µs ± 1%  68.2µs ± 0%  -18.27%  (p=0.000 n=10+10)
GlyphAlphaLoose128Src-8   59.8µs ± 0%  47.4µs ± 0%  -20.77%   (p=0.000 n=10+9)
GlyphAlphaLoose256Over-8   273µs ± 1%   239µs ± 0%  -12.52%   (p=0.000 n=10+9)
GlyphAlphaLoose256Src-8    187µs ± 0%   155µs ± 1%  -16.91%   (p=0.000 n=9+10)

GlyphRGBA16Over-8         5.99µs ± 0%  5.24µs ± 1%  -12.60%   (p=0.000 n=9+10)
GlyphRGBA16Src-8          5.48µs ± 0%  4.68µs ± 0%  -14.68%   (p=0.000 n=9+10)
GlyphRGBA32Over-8         14.6µs ± 0%  13.5µs ± 0%   -7.60%    (p=0.000 n=9+9)
GlyphRGBA32Src-8          12.6µs ± 0%  11.4µs ± 0%   -9.62%    (p=0.000 n=9+9)
GlyphRGBA64Over-8         44.8µs ± 0%  42.2µs ± 0%   -5.69%    (p=0.000 n=9+9)
GlyphRGBA64Src-8          36.6µs ± 1%  33.5µs ± 1%   -8.55%    (p=0.000 n=9+9)
GlyphRGBA128Over-8         162µs ± 0%   148µs ± 1%   -8.85%   (p=0.000 n=10+9)
GlyphRGBA128Src-8          129µs ± 1%   114µs ± 0%  -11.61%   (p=0.000 n=9+10)
GlyphRGBA256Over-8         588µs ± 0%   573µs ± 0%   -2.53%   (p=0.000 n=9+10)
GlyphRGBA256Src-8          455µs ± 0%   426µs ± 1%   -6.51%   (p=0.000 n=9+10)

GlyphNRGBA16Over-8        27.0µs ± 4%  26.3µs ± 2%   -2.65%   (p=0.001 n=9+10)
GlyphNRGBA16Src-8         19.4µs ± 3%  18.6µs ± 1%   -4.35%   (p=0.000 n=9+10)
GlyphNRGBA32Over-8        97.4µs ± 3%  96.8µs ± 2%     ~      (p=0.447 n=9+10)
GlyphNRGBA32Src-8         66.6µs ± 3%  64.5µs ± 1%   -3.21%   (p=0.000 n=10+9)
GlyphNRGBA64Over-8         372µs ± 3%   368µs ± 1%     ~     (p=0.105 n=10+10)
GlyphNRGBA64Src-8          235µs ± 1%   234µs ± 1%     ~       (p=0.130 n=8+8)
GlyphNRGBA128Over-8       1.45ms ± 2%  1.48ms ± 3%   +2.06%    (p=0.014 n=9+9)
GlyphNRGBA128Src-8         926µs ± 3%   937µs ± 1%     ~      (p=0.113 n=10+9)
GlyphNRGBA256Over-8       5.76ms ± 2%  5.90ms ± 3%   +2.29%   (p=0.001 n=9+10)
GlyphNRGBA256Src-8        3.59ms ± 1%  3.86ms ± 1%   +7.46%   (p=0.000 n=9+10)

Change-Id: I72f25193b5be4e57af09e9eea4eee50545a34cbf
Reviewed-on: https://go-review.googlesource.com/29972
Reviewed-by: David Crawshaw <crawshaw@golang.org>
This commit is contained in:
Nigel Tao 2016-09-28 19:29:02 +10:00
parent 8a20735b0e
commit 992afa5d48
2 changed files with 325 additions and 26 deletions

252
vector/raster_fixed.go Normal file
View File

@ -0,0 +1,252 @@
// Copyright 2016 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package vector
// This file contains a fixed point math implementation of the vector
// graphics rasterizer.
import (
"golang.org/x/image/math/f32"
)
const (
// ϕ is the number of binary digits after the fixed point.
//
// For example, if ϕ == 10 (and int1ϕ is based on the int32 type) then we
// are using 22.10 fixed point math.
//
// When changing this number, also change the assembly code (search for ϕ
// in the .s files).
ϕ = 10
one int1ϕ = 1 << ϕ
oneAndAHalf int1ϕ = 1<<ϕ + 1<<(ϕ-1)
oneMinusIota int1ϕ = 1<<ϕ - 1 // Used for rounding up.
)
// int1ϕ is a signed fixed-point number with 1*ϕ binary digits after the fixed
// point.
type int1ϕ int32
// int2ϕ is a signed fixed-point number with 2*ϕ binary digits after the fixed
// point.
//
// The Rasterizer's bufU32 field, nominally of type []uint32 (since that slice
// is also used by other code), can be thought of as a []int2ϕ during the
// fixedLineTo method. Lines of code that are actually like:
// buf[i] += uint32(etc) // buf has type []uint32.
// can be thought of as
// buf[i] += int2ϕ(etc) // buf has type []int2ϕ.
type int2ϕ int32
func fixedMax(x, y int1ϕ) int1ϕ {
if x > y {
return x
}
return y
}
func fixedMin(x, y int1ϕ) int1ϕ {
if x < y {
return x
}
return y
}
func fixedFloor(x int1ϕ) int32 { return int32(x >> ϕ) }
func fixedCeil(x int1ϕ) int32 { return int32((x + oneMinusIota) >> ϕ) }
func (z *Rasterizer) fixedLineTo(b f32.Vec2) {
a := z.pen
z.pen = b
dir := int1ϕ(1)
if a[1] > b[1] {
dir, a, b = -1, b, a
}
// Horizontal line segments yield no change in coverage. Almost horizontal
// segments would yield some change, in ideal math, but the computation
// further below, involving 1 / (b[1] - a[1]), is unstable in fixed point
// math, so we treat the segment as if it was perfectly horizontal.
if b[1]-a[1] <= 0.000001 {
return
}
dxdy := (b[0] - a[0]) / (b[1] - a[1])
ay := int1ϕ(a[1] * float32(one))
by := int1ϕ(b[1] * float32(one))
x := int1ϕ(a[0] * float32(one))
y := fixedFloor(ay)
yMax := fixedCeil(by)
if yMax > int32(z.size.Y) {
yMax = int32(z.size.Y)
}
width := int32(z.size.X)
for ; y < yMax; y++ {
dy := fixedMin(int1ϕ(y+1)<<ϕ, by) - fixedMax(int1ϕ(y)<<ϕ, ay)
xNext := x + int1ϕ(float32(dy)*dxdy)
if y < 0 {
x = xNext
continue
}
buf := z.bufU32[y*width:]
d := dy * dir
x0, x1 := x, xNext
if x > xNext {
x0, x1 = x1, x0
}
x0i := fixedFloor(x0)
x0Floor := int1ϕ(x0i) << ϕ
x1i := fixedCeil(x1)
x1Ceil := int1ϕ(x1i) << ϕ
if x1i <= x0i+1 {
xmf := (x+xNext)>>1 - x0Floor
if i := clamp(x0i+0, width); i < uint(len(buf)) {
buf[i] += uint32(d * (one - xmf))
}
if i := clamp(x0i+1, width); i < uint(len(buf)) {
buf[i] += uint32(d * xmf)
}
} else {
oneOverS := x1 - x0
twoOverS := 2 * oneOverS
x0f := x0 - x0Floor
oneMinusX0f := one - x0f
oneMinusX0fSquared := oneMinusX0f * oneMinusX0f
x1f := x1 - x1Ceil + one
x1fSquared := x1f * x1f
// These next two variables are unused, as rounding errors are
// minimized when we delay the division by oneOverS for as long as
// possible. These lines of code (and the "In ideal math" comments
// below) are commented out instead of deleted in order to aid the
// comparison with the floating point version of the rasterizer.
//
// a0 := ((oneMinusX0f * oneMinusX0f) >> 1) / oneOverS
// am := ((x1f * x1f) >> 1) / oneOverS
if i := clamp(x0i, width); i < uint(len(buf)) {
// In ideal math: buf[i] += uint32(d * a0)
D := oneMinusX0fSquared
D *= d
D /= twoOverS
buf[i] += uint32(D)
}
if x1i == x0i+2 {
if i := clamp(x0i+1, width); i < uint(len(buf)) {
// In ideal math: buf[i] += uint32(d * (one - a0 - am))
D := twoOverS<<ϕ - oneMinusX0fSquared - x1fSquared
D *= d
D /= twoOverS
buf[i] += uint32(D)
}
} else {
// This is commented out for the same reason as a0 and am.
//
// a1 := ((oneAndAHalf - x0f) << ϕ) / oneOverS
if i := clamp(x0i+1, width); i < uint(len(buf)) {
// In ideal math: buf[i] += uint32(d * (a1 - a0))
//
// Convert to int64 to avoid overflow. Without that,
// TestRasterizePolygon fails.
D := int64((oneAndAHalf-x0f)<<(ϕ+1) - oneMinusX0fSquared)
D *= int64(d)
D /= int64(twoOverS)
buf[i] += uint32(D)
}
dTimesS := uint32((d << (2 * ϕ)) / oneOverS)
for xi := x0i + 2; xi < x1i-1; xi++ {
if i := clamp(xi, width); i < uint(len(buf)) {
buf[i] += dTimesS
}
}
// This is commented out for the same reason as a0 and am.
//
// a2 := a1 + (int1ϕ(x1i-x0i-3)<<(2*ϕ))/oneOverS
if i := clamp(x1i-1, width); i < uint(len(buf)) {
// In ideal math: buf[i] += uint32(d * (one - a2 - am))
//
// Convert to int64 to avoid overflow. Without that,
// TestRasterizePolygon fails.
D := int64(twoOverS << ϕ)
D -= int64((oneAndAHalf - x0f) << (ϕ + 1))
D -= int64((x1i - x0i - 3) << (2*ϕ + 1))
D -= int64(x1fSquared)
D *= int64(d)
D /= int64(twoOverS)
buf[i] += uint32(D)
}
}
if i := clamp(x1i, width); i < uint(len(buf)) {
// In ideal math: buf[i] += uint32(d * am)
D := x1fSquared
D *= d
D /= twoOverS
buf[i] += uint32(D)
}
}
x = xNext
}
}
func fixedAccumulateOpSrc(dst []uint8, src []uint32) {
acc := int2ϕ(0)
for i, v := range src {
acc += int2ϕ(v)
a := acc
if a < 0 {
a = -a
}
a >>= 2*ϕ - 8
if a > 0xff {
a = 0xff
}
dst[i] = uint8(a)
}
}
func fixedAccumulateOpOver(dst []uint8, src []uint32) {
acc := int2ϕ(0)
for i, v := range src {
acc += int2ϕ(v)
a := acc
if a < 0 {
a = -a
}
a >>= 2*ϕ - 16
if a > 0xffff {
a = 0xffff
}
// This algorithm comes from the standard library's image/draw package.
dstA := uint32(dst[i]) * 0x101
maskA := uint32(a)
outA := dstA*(0xffff-maskA)/0xffff + maskA
dst[i] = uint8(outA >> 8)
}
}
func fixedAccumulateMask(buf []uint32) {
acc := int2ϕ(0)
for i, v := range buf {
acc += int2ϕ(v)
a := acc
if a < 0 {
a = -a
}
a >>= 2*ϕ - 16
if a > 0xffff {
a = 0xffff
}
buf[i] = uint32(a)
}
}

View File

@ -25,6 +25,26 @@ import (
"golang.org/x/image/math/f32"
)
// floatingPointMathThreshold is the width or hight above which the rasterizer
// chooses to used floating point math instead of fixed point math.
//
// Both implementations of line segmentation rasterization (see raster_fixed.go
// and raster_floating.go) implement the same algorithm (in ideal, infinite
// precision math) but they perform differently in practice. The fixed point
// math version is roughtly 1.25x faster (on GOARCH=amd64) on the benchmarks,
// but at sufficiently large scales, the computations will overflow and hence
// show rendering artifacts. The floating point math version has more
// consistent quality over larger scales, but it is significantly slower.
//
// This constant determines when to use the faster implementation and when to
// use the better quality implementation.
//
// The rationale for this particular value is that TestRasterizePolygon in
// vector_test.go checks the rendering quality of polygon edges at various
// angles, inscribed in a circle of diameter 2048. It may be that a higher
// value would still produce acceptable quality, but 2048 seems to work.
const floatingPointMathThreshold = 2048
func midPoint(p, q f32.Vec2) f32.Vec2 {
return f32.Vec2{
(p[0] + q[0]) * 0.5,
@ -52,10 +72,9 @@ func clamp(i, width int32) uint {
// NewRasterizer returns a new Rasterizer whose rendered mask image is bounded
// by the given width and height.
func NewRasterizer(w, h int) *Rasterizer {
return &Rasterizer{
bufF32: make([]float32, w*h),
size: image.Point{w, h},
}
z := &Rasterizer{}
z.Reset(w, h)
return z
}
// Raster is a 2-D vector graphics rasterizer.
@ -77,11 +96,11 @@ type Rasterizer struct {
// bufU32[i] = math.Float32bits(x + math.Float32frombits(bufU32[i]))
//
// See golang.org/issue/17220 for some discussion.
//
// TODO: use bufU32 in the fixed point math implementation.
bufF32 []float32
bufU32 []uint32
useFloatingPointMath bool
size image.Point
first f32.Vec2
pen f32.Vec2
@ -99,6 +118,15 @@ type Rasterizer struct {
//
// This includes setting z.DrawOp to draw.Over.
func (z *Rasterizer) Reset(w, h int) {
z.size = image.Point{w, h}
z.first = f32.Vec2{}
z.pen = f32.Vec2{}
z.DrawOp = draw.Over
z.useFloatingPointMath = w > floatingPointMathThreshold || h > floatingPointMathThreshold
// Make z.bufF32 or z.bufU32 large enough to hold w*h samples.
if z.useFloatingPointMath {
if n := w * h; n > cap(z.bufF32) {
z.bufF32 = make([]float32, n)
} else {
@ -107,10 +135,16 @@ func (z *Rasterizer) Reset(w, h int) {
z.bufF32[i] = 0
}
}
z.size = image.Point{w, h}
z.first = f32.Vec2{}
z.pen = f32.Vec2{}
z.DrawOp = draw.Over
} else {
if n := w * h; n > cap(z.bufU32) {
z.bufU32 = make([]uint32, n)
} else {
z.bufU32 = z.bufU32[:n]
for i := range z.bufU32 {
z.bufU32[i] = 0
}
}
}
}
// Size returns the width and height passed to NewRasterizer or Reset.
@ -147,8 +181,11 @@ func (z *Rasterizer) MoveTo(a f32.Vec2) {
//
// The coordinates are allowed to be out of the Rasterizer's bounds.
func (z *Rasterizer) LineTo(b f32.Vec2) {
// TODO: add a fixed point math implementation.
if z.useFloatingPointMath {
z.floatingLineTo(b)
} else {
z.fixedLineTo(b)
}
}
// QuadTo adds a quadratic Bézier segment, from the pen via b to c, and moves
@ -258,22 +295,29 @@ func (z *Rasterizer) Draw(dst draw.Image, r image.Rectangle, src image.Image, sp
}
func (z *Rasterizer) accumulateMask() {
if z.useFloatingPointMath {
if n := z.size.X * z.size.Y; n > cap(z.bufU32) {
z.bufU32 = make([]uint32, n)
} else {
z.bufU32 = z.bufU32[:n]
}
floatingAccumulateMask(z.bufU32, z.bufF32)
} else {
fixedAccumulateMask(z.bufU32)
}
}
func (z *Rasterizer) rasterizeDstAlphaSrcOpaqueOpOver(dst *image.Alpha, r image.Rectangle) {
// TODO: add SIMD implementations.
// TODO: add a fixed point math implementation.
// TODO: non-zero vs even-odd winding?
if r == dst.Bounds() && r == z.Bounds() {
// We bypass the z.accumulateMask step and convert straight from
// z.bufF32 to dst.Pix.
// z.bufF32 or z.bufU32 to dst.Pix.
if z.useFloatingPointMath {
floatingAccumulateOpOver(dst.Pix, z.bufF32)
} else {
fixedAccumulateOpOver(dst.Pix, z.bufU32)
}
return
}
@ -294,12 +338,15 @@ func (z *Rasterizer) rasterizeDstAlphaSrcOpaqueOpOver(dst *image.Alpha, r image.
func (z *Rasterizer) rasterizeDstAlphaSrcOpaqueOpSrc(dst *image.Alpha, r image.Rectangle) {
// TODO: add SIMD implementations.
// TODO: add a fixed point math implementation.
// TODO: non-zero vs even-odd winding?
if r == dst.Bounds() && r == z.Bounds() {
// We bypass the z.accumulateMask step and convert straight from
// z.bufF32 to dst.Pix.
// z.bufF32 or z.bufU32 to dst.Pix.
if z.useFloatingPointMath {
floatingAccumulateOpSrc(dst.Pix, z.bufF32)
} else {
fixedAccumulateOpSrc(dst.Pix, z.bufU32)
}
return
}