From 500caaeda74dd9c660279036293f4b2997cf0b03 Mon Sep 17 00:00:00 2001 From: Dimitri Sokolyuk Date: Sat, 9 Sep 2017 09:42:37 +0200 Subject: Add vendor --- .../golang.org/x/image/vector/raster_floating.go | 220 +++++++++++++++++++++ 1 file changed, 220 insertions(+) create mode 100644 vendor/golang.org/x/image/vector/raster_floating.go (limited to 'vendor/golang.org/x/image/vector/raster_floating.go') diff --git a/vendor/golang.org/x/image/vector/raster_floating.go b/vendor/golang.org/x/image/vector/raster_floating.go new file mode 100644 index 0000000..fd11db1 --- /dev/null +++ b/vendor/golang.org/x/image/vector/raster_floating.go @@ -0,0 +1,220 @@ +// 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 floating point math implementation of the vector +// graphics rasterizer. + +import ( + "math" +) + +func floatingMax(x, y float32) float32 { + if x > y { + return x + } + return y +} + +func floatingMin(x, y float32) float32 { + if x < y { + return x + } + return y +} + +func floatingFloor(x float32) int32 { return int32(math.Floor(float64(x))) } +func floatingCeil(x float32) int32 { return int32(math.Ceil(float64(x))) } + +func (z *Rasterizer) floatingLineTo(bx, by float32) { + ax, ay := z.penX, z.penY + z.penX, z.penY = bx, by + dir := float32(1) + if ay > by { + dir, ax, ay, bx, by = -1, bx, by, ax, ay + } + // 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 / (by - ay), is unstable in floating point + // math, so we treat the segment as if it was perfectly horizontal. + if by-ay <= 0.000001 { + return + } + dxdy := (bx - ax) / (by - ay) + + x := ax + y := floatingFloor(ay) + yMax := floatingCeil(by) + if yMax > int32(z.size.Y) { + yMax = int32(z.size.Y) + } + width := int32(z.size.X) + + for ; y < yMax; y++ { + dy := floatingMin(float32(y+1), by) - floatingMax(float32(y), ay) + + // The "float32" in expressions like "float32(foo*bar)" here and below + // look redundant, since foo and bar already have type float32, but are + // explicit in order to disable the compiler's Fused Multiply Add (FMA) + // instruction selection, which can improve performance but can result + // in different rounding errors in floating point computations. + // + // This package aims to have bit-exact identical results across all + // GOARCHes, and across pure Go code and assembly, so it disables FMA. + // + // See the discussion at + // https://groups.google.com/d/topic/golang-dev/Sti0bl2xUXQ/discussion + xNext := x + float32(dy*dxdy) + if y < 0 { + x = xNext + continue + } + buf := z.bufF32[y*width:] + d := float32(dy * dir) + x0, x1 := x, xNext + if x > xNext { + x0, x1 = x1, x0 + } + x0i := floatingFloor(x0) + x0Floor := float32(x0i) + x1i := floatingCeil(x1) + x1Ceil := float32(x1i) + + if x1i <= x0i+1 { + xmf := float32(0.5*(x+xNext)) - x0Floor + if i := clamp(x0i+0, width); i < uint(len(buf)) { + buf[i] += d - float32(d*xmf) + } + if i := clamp(x0i+1, width); i < uint(len(buf)) { + buf[i] += float32(d * xmf) + } + } else { + s := 1 / (x1 - x0) + x0f := x0 - x0Floor + oneMinusX0f := 1 - x0f + a0 := float32(0.5 * s * oneMinusX0f * oneMinusX0f) + x1f := x1 - x1Ceil + 1 + am := float32(0.5 * s * x1f * x1f) + + if i := clamp(x0i, width); i < uint(len(buf)) { + buf[i] += float32(d * a0) + } + + if x1i == x0i+2 { + if i := clamp(x0i+1, width); i < uint(len(buf)) { + buf[i] += float32(d * (1 - a0 - am)) + } + } else { + a1 := float32(s * (1.5 - x0f)) + if i := clamp(x0i+1, width); i < uint(len(buf)) { + buf[i] += float32(d * (a1 - a0)) + } + dTimesS := float32(d * s) + for xi := x0i + 2; xi < x1i-1; xi++ { + if i := clamp(xi, width); i < uint(len(buf)) { + buf[i] += dTimesS + } + } + a2 := a1 + float32(s*float32(x1i-x0i-3)) + if i := clamp(x1i-1, width); i < uint(len(buf)) { + buf[i] += float32(d * (1 - a2 - am)) + } + } + + if i := clamp(x1i, width); i < uint(len(buf)) { + buf[i] += float32(d * am) + } + } + + x = xNext + } +} + +const ( + // almost256 scales a floating point value in the range [0, 1] to a uint8 + // value in the range [0x00, 0xff]. + // + // 255 is too small. Floating point math accumulates rounding errors, so a + // fully covered src value that would in ideal math be float32(1) might be + // float32(1-ε), and uint8(255 * (1-ε)) would be 0xfe instead of 0xff. The + // uint8 conversion rounds to zero, not to nearest. + // + // 256 is too big. If we multiplied by 256, below, then a fully covered src + // value of float32(1) would translate to uint8(256 * 1), which can be 0x00 + // instead of the maximal value 0xff. + // + // math.Float32bits(almost256) is 0x437fffff. + almost256 = 255.99998 + + // almost65536 scales a floating point value in the range [0, 1] to a + // uint16 value in the range [0x0000, 0xffff]. + // + // math.Float32bits(almost65536) is 0x477fffff. + almost65536 = almost256 * 256 +) + +func floatingAccumulateOpOver(dst []uint8, src []float32) { + // Sanity check that len(dst) >= len(src). + if len(dst) < len(src) { + return + } + + acc := float32(0) + for i, v := range src { + acc += v + a := acc + if a < 0 { + a = -a + } + if a > 1 { + a = 1 + } + // This algorithm comes from the standard library's image/draw package. + dstA := uint32(dst[i]) * 0x101 + maskA := uint32(almost65536 * a) + outA := dstA*(0xffff-maskA)/0xffff + maskA + dst[i] = uint8(outA >> 8) + } +} + +func floatingAccumulateOpSrc(dst []uint8, src []float32) { + // Sanity check that len(dst) >= len(src). + if len(dst) < len(src) { + return + } + + acc := float32(0) + for i, v := range src { + acc += v + a := acc + if a < 0 { + a = -a + } + if a > 1 { + a = 1 + } + dst[i] = uint8(almost256 * a) + } +} + +func floatingAccumulateMask(dst []uint32, src []float32) { + // Sanity check that len(dst) >= len(src). + if len(dst) < len(src) { + return + } + + acc := float32(0) + for i, v := range src { + acc += v + a := acc + if a < 0 { + a = -a + } + if a > 1 { + a = 1 + } + dst[i] = uint32(almost65536 * a) + } +} -- cgit v1.2.3