forked from golang/exp
/
buffer.go
259 lines (234 loc) · 5.22 KB
/
buffer.go
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// 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 iconvg
import (
"image/color"
"math"
)
// buffer holds an encoded IconVG graphic.
//
// The decodeXxx methods return the decoded value and an integer n, the number
// of bytes that value was encoded in. They return n == 0 if an error occured.
//
// The encodeXxx methods append to the buffer, modifying the slice in place.
type buffer []byte
func (b buffer) decodeNatural() (u uint32, n int) {
if len(b) < 1 {
return 0, 0
}
x := b[0]
if x&0x01 == 0 {
return uint32(x) >> 1, 1
}
if x&0x02 == 0 {
if len(b) >= 2 {
y := uint16(b[0]) | uint16(b[1])<<8
return uint32(y) >> 2, 2
}
return 0, 0
}
if len(b) >= 4 {
y := uint32(b[0]) | uint32(b[1])<<8 | uint32(b[2])<<16 | uint32(b[3])<<24
return y >> 2, 4
}
return 0, 0
}
func (b buffer) decodeReal() (f float32, n int) {
switch u, n := b.decodeNatural(); n {
case 0:
return 0, n
case 1:
return float32(u), n
case 2:
return float32(u), n
default:
return math.Float32frombits(u << 2), n
}
}
func (b buffer) decodeCoordinate() (f float32, n int) {
switch u, n := b.decodeNatural(); n {
case 0:
return 0, n
case 1:
return float32(int32(u) - 64), n
case 2:
return float32(int32(u)-64*128) / 64, n
default:
return math.Float32frombits(u << 2), n
}
}
func (b buffer) decodeZeroToOne() (f float32, n int) {
switch u, n := b.decodeNatural(); n {
case 0:
return 0, n
case 1:
return float32(u) / 120, n
case 2:
return float32(u) / 15120, n
default:
return math.Float32frombits(u << 2), n
}
}
func (b buffer) decodeColor1() (c Color, n int) {
if len(b) < 1 {
return Color{}, 0
}
return decodeColor1(b[0]), 1
}
func (b buffer) decodeColor2() (c Color, n int) {
if len(b) < 2 {
return Color{}, 0
}
return RGBAColor(color.RGBA{
R: 0x11 * (b[0] >> 4),
G: 0x11 * (b[0] & 0x0f),
B: 0x11 * (b[1] >> 4),
A: 0x11 * (b[1] & 0x0f),
}), 2
}
func (b buffer) decodeColor3Direct() (c Color, n int) {
if len(b) < 3 {
return Color{}, 0
}
return RGBAColor(color.RGBA{
R: b[0],
G: b[1],
B: b[2],
A: 0xff,
}), 3
}
func (b buffer) decodeColor4() (c Color, n int) {
if len(b) < 4 {
return Color{}, 0
}
return RGBAColor(color.RGBA{
R: b[0],
G: b[1],
B: b[2],
A: b[3],
}), 4
}
func (b buffer) decodeColor3Indirect() (c Color, n int) {
if len(b) < 3 {
return Color{}, 0
}
return BlendColor(b[0], b[1], b[2]), 3
}
func (b *buffer) encodeNatural(u uint32) {
if u < 1<<7 {
u = (u << 1)
*b = append(*b, uint8(u))
return
}
if u < 1<<14 {
u = (u << 2) | 1
*b = append(*b, uint8(u), uint8(u>>8))
return
}
u = (u << 2) | 3
*b = append(*b, uint8(u), uint8(u>>8), uint8(u>>16), uint8(u>>24))
}
func (b *buffer) encodeReal(f float32) int {
if u := uint32(f); float32(u) == f && u < 1<<14 {
if u < 1<<7 {
u = (u << 1)
*b = append(*b, uint8(u))
return 1
}
u = (u << 2) | 1
*b = append(*b, uint8(u), uint8(u>>8))
return 2
}
b.encode4ByteReal(f)
return 4
}
func (b *buffer) encode4ByteReal(f float32) {
u := math.Float32bits(f)
// Round the fractional bits (the low 23 bits) to the nearest multiple of
// 4, being careful not to overflow into the upper bits.
v := u & 0x007fffff
if v < 0x007ffffe {
v += 2
}
u = (u & 0xff800000) | v
// A 4 byte encoding has the low two bits set.
u |= 0x03
*b = append(*b, uint8(u), uint8(u>>8), uint8(u>>16), uint8(u>>24))
}
func (b *buffer) encodeCoordinate(f float32) int {
if i := int32(f); -64 <= i && i < +64 && float32(i) == f {
u := uint32(i + 64)
u = (u << 1)
*b = append(*b, uint8(u))
return 1
}
if i := int32(f * 64); -128*64 <= i && i < +128*64 && float32(i) == f*64 {
u := uint32(i + 128*64)
u = (u << 2) | 1
*b = append(*b, uint8(u), uint8(u>>8))
return 2
}
b.encode4ByteReal(f)
return 4
}
func (b *buffer) encodeAngle(f float32) int {
// Normalize f to the range [0, 1).
g := float64(f)
g -= math.Floor(g)
return b.encodeZeroToOne(float32(g))
}
func (b *buffer) encodeZeroToOne(f float32) int {
if u := uint32(f * 15120); float32(u) == f*15120 && u < 15120 {
if u%126 == 0 {
u = ((u / 126) << 1)
*b = append(*b, uint8(u))
return 1
}
u = (u << 2) | 1
*b = append(*b, uint8(u), uint8(u>>8))
return 2
}
b.encode4ByteReal(f)
return 4
}
func (b *buffer) encodeColor1(c Color) {
if x, ok := encodeColor1(c); ok {
*b = append(*b, x)
return
}
// Default to opaque black.
*b = append(*b, 0x00)
}
func (b *buffer) encodeColor2(c Color) {
if x, ok := encodeColor2(c); ok {
*b = append(*b, x[0], x[1])
return
}
// Default to opaque black.
*b = append(*b, 0x00, 0x0f)
}
func (b *buffer) encodeColor3Direct(c Color) {
if x, ok := encodeColor3Direct(c); ok {
*b = append(*b, x[0], x[1], x[2])
return
}
// Default to opaque black.
*b = append(*b, 0x00, 0x00, 0x00)
}
func (b *buffer) encodeColor4(c Color) {
if x, ok := encodeColor4(c); ok {
*b = append(*b, x[0], x[1], x[2], x[3])
return
}
// Default to opaque black.
*b = append(*b, 0x00, 0x00, 0x00, 0xff)
}
func (b *buffer) encodeColor3Indirect(c Color) {
if x, ok := encodeColor3Indirect(c); ok {
*b = append(*b, x[0], x[1], x[2])
return
}
// Default to opaque black.
*b = append(*b, 0x00, 0x00, 0x00)
}