golang-image/vector/vector.go
Nigel Tao 0080ac3d2c vector: add some more tests.
These tests are copied from the github.com/google/font-go prototype.

Change-Id: I4523193bd3453974633cbef0576c1203eb013a7d
Reviewed-on: https://go-review.googlesource.com/29697
Reviewed-by: David Crawshaw <crawshaw@golang.org>
2016-09-25 03:45:43 +00:00

355 lines
10 KiB
Go

// 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 provides a rasterizer for 2-D vector graphics.
package vector // import "golang.org/x/image/vector"
// The rasterizer's design follows
// https://medium.com/@raphlinus/inside-the-fastest-font-renderer-in-the-world-75ae5270c445
//
// Proof of concept code is in
// https://github.com/google/font-go
//
// See also:
// http://nothings.org/gamedev/rasterize/
// http://projects.tuxee.net/cl-vectors/section-the-cl-aa-algorithm
// https://people.gnome.org/~mathieu/libart/internals.html#INTERNALS-SCANLINE
import (
"image"
"image/color"
"image/draw"
"math"
"golang.org/x/image/math/f32"
)
func midPoint(p, q f32.Vec2) f32.Vec2 {
return f32.Vec2{
(p[0] + q[0]) * 0.5,
(p[1] + q[1]) * 0.5,
}
}
func lerp(t float32, p, q f32.Vec2) f32.Vec2 {
return f32.Vec2{
p[0] + t*(q[0]-p[0]),
p[1] + t*(q[1]-p[1]),
}
}
func clamp(i, width int32) uint {
if i < 0 {
return 0
}
if i < width {
return uint(i)
}
return uint(width)
}
// 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},
}
}
// Raster is a 2-D vector graphics rasterizer.
//
// The zero value is usable, in that it is a Rasterizer whose rendered mask
// image has zero width and zero height. Call Reset to change its bounds.
type Rasterizer struct {
// bufXxx are buffers of float32 or uint32 values, holding either the
// individual or cumulative area values.
//
// We don't actually need both values at any given time, and to conserve
// memory, the integration of the individual to the cumulative could modify
// the buffer in place. In other words, we could use a single buffer, say
// of type []uint32, and add some math.Float32bits and math.Float32frombits
// calls to satisfy the compiler's type checking. As of Go 1.7, though,
// there is a performance penalty between:
// bufF32[i] += x
// and
// 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
size image.Point
first f32.Vec2
pen f32.Vec2
// DrawOp is the operator used for the Draw method.
//
// The zero value is draw.Over.
DrawOp draw.Op
// TODO: an exported field equivalent to the mask point in the
// draw.DrawMask function in the stdlib image/draw package?
}
// Reset resets a Rasterizer as if it was just returned by NewRasterizer.
//
// This includes setting z.DrawOp to draw.Over.
func (z *Rasterizer) Reset(w, h int) {
if n := w * h; n > cap(z.bufF32) {
z.bufF32 = make([]float32, n)
} else {
z.bufF32 = z.bufF32[:n]
for i := range z.bufF32 {
z.bufF32[i] = 0
}
}
z.size = image.Point{w, h}
z.first = f32.Vec2{}
z.pen = f32.Vec2{}
z.DrawOp = draw.Over
}
// Size returns the width and height passed to NewRasterizer or Reset.
func (z *Rasterizer) Size() image.Point {
return z.size
}
// Bounds returns the rectangle from (0, 0) to the width and height passed to
// NewRasterizer or Reset.
func (z *Rasterizer) Bounds() image.Rectangle {
return image.Rectangle{Max: z.size}
}
// Pen returns the location of the path-drawing pen: the last argument to the
// most recent XxxTo call.
func (z *Rasterizer) Pen() f32.Vec2 {
return z.pen
}
// ClosePath closes the current path.
func (z *Rasterizer) ClosePath() {
z.LineTo(z.first)
}
// MoveTo starts a new path and moves the pen to a.
//
// The coordinates are allowed to be out of the Rasterizer's bounds.
func (z *Rasterizer) MoveTo(a f32.Vec2) {
z.first = a
z.pen = a
}
// LineTo adds a line segment, from the pen to b, and moves the pen to b.
//
// 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.
z.floatingLineTo(b)
}
// QuadTo adds a quadratic Bézier segment, from the pen via b to c, and moves
// the pen to c.
//
// The coordinates are allowed to be out of the Rasterizer's bounds.
func (z *Rasterizer) QuadTo(b, c f32.Vec2) {
a := z.pen
devsq := devSquared(a, b, c)
if devsq >= 0.333 {
const tol = 3
n := 1 + int(math.Sqrt(math.Sqrt(tol*float64(devsq))))
t, nInv := float32(0), 1/float32(n)
for i := 0; i < n-1; i++ {
t += nInv
ab := lerp(t, a, b)
bc := lerp(t, b, c)
z.LineTo(lerp(t, ab, bc))
}
}
z.LineTo(c)
}
// CubeTo adds a cubic Bézier segment, from the pen via b and c to d, and moves
// the pen to d.
//
// The coordinates are allowed to be out of the Rasterizer's bounds.
func (z *Rasterizer) CubeTo(b, c, d f32.Vec2) {
a := z.pen
devsq := devSquared(a, b, d)
if devsqAlt := devSquared(a, c, d); devsq < devsqAlt {
devsq = devsqAlt
}
if devsq >= 0.333 {
const tol = 3
n := 1 + int(math.Sqrt(math.Sqrt(tol*float64(devsq))))
t, nInv := float32(0), 1/float32(n)
for i := 0; i < n-1; i++ {
t += nInv
ab := lerp(t, a, b)
bc := lerp(t, b, c)
cd := lerp(t, c, d)
abc := lerp(t, ab, bc)
bcd := lerp(t, bc, cd)
z.LineTo(lerp(t, abc, bcd))
}
}
z.LineTo(d)
}
// devSquared returns a measure of how curvy the sequnce a to b to c is. It
// determines how many line segments will approximate a Bézier curve segment.
//
// http://lists.nongnu.org/archive/html/freetype-devel/2016-08/msg00080.html
// gives the rationale for this evenly spaced heuristic instead of a recursive
// de Casteljau approach:
//
// The reason for the subdivision by n is that I expect the "flatness"
// computation to be semi-expensive (it's done once rather than on each
// potential subdivision) and also because you'll often get fewer subdivisions.
// Taking a circular arc as a simplifying assumption (ie a spherical cow),
// where I get n, a recursive approach would get 2^⌈lg n⌉, which, if I haven't
// made any horrible mistakes, is expected to be 33% more in the limit.
func devSquared(a, b, c f32.Vec2) float32 {
devx := a[0] - 2*b[0] + c[0]
devy := a[1] - 2*b[1] + c[1]
return devx*devx + devy*devy
}
// Draw implements the Drawer interface from the standard library's image/draw
// package.
//
// The vector paths previously added via the XxxTo calls become the mask for
// drawing src onto dst.
func (z *Rasterizer) Draw(dst draw.Image, r image.Rectangle, src image.Image, sp image.Point) {
// TODO: adjust r and sp (and mp?) if src.Bounds() doesn't contain
// r.Add(sp.Sub(r.Min)).
if src, ok := src.(*image.Uniform); ok {
_, _, _, srcA := src.RGBA()
switch dst := dst.(type) {
case *image.Alpha:
// Fast path for glyph rendering.
if srcA == 0xffff {
if z.DrawOp == draw.Over {
z.rasterizeDstAlphaSrcOpaqueOpOver(dst, r)
} else {
z.rasterizeDstAlphaSrcOpaqueOpSrc(dst, r)
}
return
}
}
}
if z.DrawOp == draw.Over {
z.rasterizeOpOver(dst, r, src, sp)
} else {
z.rasterizeOpSrc(dst, r, src, sp)
}
}
func (z *Rasterizer) accumulateMask() {
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)
}
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.
floatingAccumulateOpOver(dst.Pix, z.bufF32)
return
}
z.accumulateMask()
pix := dst.Pix[dst.PixOffset(r.Min.X, r.Min.Y):]
for y, y1 := 0, r.Max.Y-r.Min.Y; y < y1; y++ {
for x, x1 := 0, r.Max.X-r.Min.X; x < x1; x++ {
ma := z.bufU32[y*z.size.X+x]
i := y*dst.Stride + x
// This formula is like rasterizeOpOver's, simplified for the
// concrete dst type and opaque src assumption.
a := 0xffff - ma
pix[i] = uint8((uint32(pix[i])*0x101*a/0xffff + ma) >> 8)
}
}
}
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.
floatingAccumulateOpSrc(dst.Pix, z.bufF32)
return
}
z.accumulateMask()
pix := dst.Pix[dst.PixOffset(r.Min.X, r.Min.Y):]
for y, y1 := 0, r.Max.Y-r.Min.Y; y < y1; y++ {
for x, x1 := 0, r.Max.X-r.Min.X; x < x1; x++ {
ma := z.bufU32[y*z.size.X+x]
// This formula is like rasterizeOpSrc's, simplified for the
// concrete dst type and opaque src assumption.
pix[y*dst.Stride+x] = uint8(ma >> 8)
}
}
}
func (z *Rasterizer) rasterizeOpOver(dst draw.Image, r image.Rectangle, src image.Image, sp image.Point) {
z.accumulateMask()
out := color.RGBA64{}
outc := color.Color(&out)
for y, y1 := 0, r.Max.Y-r.Min.Y; y < y1; y++ {
for x, x1 := 0, r.Max.X-r.Min.X; x < x1; x++ {
sr, sg, sb, sa := src.At(sp.X+x, sp.Y+y).RGBA()
ma := z.bufU32[y*z.size.X+x]
// This algorithm comes from the standard library's image/draw
// package.
dr, dg, db, da := dst.At(r.Min.X+x, r.Min.Y+y).RGBA()
a := 0xffff - (sa * ma / 0xffff)
out.R = uint16((dr*a + sr*ma) / 0xffff)
out.G = uint16((dg*a + sg*ma) / 0xffff)
out.B = uint16((db*a + sb*ma) / 0xffff)
out.A = uint16((da*a + sa*ma) / 0xffff)
dst.Set(r.Min.X+x, r.Min.Y+y, outc)
}
}
}
func (z *Rasterizer) rasterizeOpSrc(dst draw.Image, r image.Rectangle, src image.Image, sp image.Point) {
z.accumulateMask()
out := color.RGBA64{}
outc := color.Color(&out)
for y, y1 := 0, r.Max.Y-r.Min.Y; y < y1; y++ {
for x, x1 := 0, r.Max.X-r.Min.X; x < x1; x++ {
sr, sg, sb, sa := src.At(sp.X+x, sp.Y+y).RGBA()
ma := z.bufU32[y*z.size.X+x]
// This algorithm comes from the standard library's image/draw
// package.
out.R = uint16(sr * ma / 0xffff)
out.G = uint16(sg * ma / 0xffff)
out.B = uint16(sb * ma / 0xffff)
out.A = uint16(sa * ma / 0xffff)
dst.Set(r.Min.X+x, r.Min.Y+y, outc)
}
}
}