110 lines
2.8 KiB
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)}
|
||
|
|
}
|