GoToSocial/vendor/github.com/buckket/go-blurhash/decode.go

110 lines
2.8 KiB
Go

package blurhash
import (
"fmt"
"github.com/buckket/go-blurhash/base83"
"image"
"image/color"
"math"
)
// An InvalidHashError occurs when the given hash is either too short or the length does not match its size flag.
type InvalidHashError string
func (e InvalidHashError) Error() string {
return fmt.Sprintf("blurhash: %s", string(e))
}
// Components decodes and returns the number of x and y components in the given BlurHash.
func Components(hash string) (xComponents, yComponents int, err error) {
if len(hash) < 6 {
return 0, 0, InvalidHashError("hash is invalid (too short)")
}
sizeFlag, err := base83.Decode(string(hash[0]))
if err != nil {
return 0, 0, err
}
yComponents = (sizeFlag / 9) + 1
xComponents = (sizeFlag % 9) + 1
if len(hash) != 4+2*xComponents*yComponents {
return 0, 0, InvalidHashError("hash is invalid (length mismatch)")
}
return xComponents, yComponents, nil
}
// Decode generates an image of the given BlurHash with a size of width and height.
// Punch is a multiplier that adjusts the contrast of the resulting image.
func Decode(hash string, width, height, punch int) (image.Image, error) {
xComp, yComp, err := Components(hash)
if err != nil {
return nil, err
}
quantisedMaximumValue, err := base83.Decode(string(hash[1]))
if err != nil {
return nil, err
}
maximumValue := (float64(quantisedMaximumValue) + 1) / 166
if punch == 0 {
punch = 1
}
colors := make([][3]float64, xComp*yComp)
for i := range colors {
if i == 0 {
value, err := base83.Decode(hash[2:6])
if err != nil {
return nil, err
}
colors[i] = decodeDC(value)
} else {
value, err := base83.Decode(hash[4+i*2 : 6+i*2])
if err != nil {
return nil, err
}
colors[i] = decodeAC(value, maximumValue*float64(punch))
}
}
img := image.NewNRGBA(image.Rect(0, 0, width, height))
for y := 0; y < height; y++ {
for x := 0; x < width; x++ {
var r, g, b float64
for j := 0; j < yComp; j++ {
for i := 0; i < xComp; i++ {
basis := math.Cos(math.Pi*float64(x)*float64(i)/float64(width)) *
math.Cos(math.Pi*float64(y)*float64(j)/float64(height))
pcolor := colors[i+j*xComp]
r += pcolor[0] * basis
g += pcolor[1] * basis
b += pcolor[2] * basis
}
}
img.SetNRGBA(x, y, color.NRGBA{R: uint8(linearTosRGB(r)), G: uint8(linearTosRGB(g)), B: uint8(linearTosRGB(b)), A: 255})
}
}
return img, nil
}
func decodeDC(value int) [3]float64 {
return [3]float64{sRGBToLinear(value >> 16), sRGBToLinear(value >> 8 & 255), sRGBToLinear(value & 255)}
}
func decodeAC(value int, maximumValue float64) [3]float64 {
quantR := math.Floor(float64(value) / (19 * 19))
quantG := math.Mod(math.Floor(float64(value)/19), 19)
quantB := math.Mod(float64(value), 19)
sp := func(quant float64) float64 {
return signPow((quant-9)/9, 2.0) * maximumValue
}
return [3]float64{sp(quantR), sp(quantG), sp(quantB)}
}