1 files changed, 164 insertions, 0 deletions
diff --git a/vendor/github.com/buckket/go-blurhash/encode.go b/vendor/github.com/buckket/go-blurhash/encode.go
new file mode 100644
index 000000000..dd1cdec6f
--- /dev/null
+++ b/vendor/github.com/buckket/go-blurhash/encode.go
@@ -0,0 +1,164 @@
+package blurhash
+
+import (
+	"fmt"
+	"github.com/buckket/go-blurhash/base83"
+	"image"
+	"math"
+	"strings"
+)
+
+func init() {
+	initLinearTable(channelToLinear[:])
+}
+
+var channelToLinear [256]float64
+
+func initLinearTable(table []float64) {
+	for i := range table {
+		channelToLinear[i] = sRGBToLinear(i)
+	}
+}
+
+// An InvalidParameterError occurs when an invalid argument is passed to either the Decode or Encode function.
+type InvalidParameterError struct {
+	Value     int
+	Parameter string
+}
+
+func (e InvalidParameterError) Error() string {
+	return fmt.Sprintf("blurhash: %sComponents (%d) must be element of [1-9]", e.Parameter, e.Value)
+}
+
+// An EncodingError represents an error that occurred during the encoding of the given value.
+// This most likely means that your input image is invalid and can not be processed.
+type EncodingError string
+
+func (e EncodingError) Error() string {
+	return fmt.Sprintf("blurhash: %s", string(e))
+}
+
+// Encode calculates the Blurhash for an image using the given x and y component counts.
+// The x and y components have to be between 1 and 9 respectively.
+// The image must be of image.Image type.
+func Encode(xComponents int, yComponents int, rgba image.Image) (string, error) {
+	if xComponents < 1 || xComponents > 9 {
+		return "", InvalidParameterError{xComponents, "x"}
+	}
+	if yComponents < 1 || yComponents > 9 {
+		return "", InvalidParameterError{yComponents, "y"}
+	}
+
+	var blurhash strings.Builder
+	blurhash.Grow(4 + 2*xComponents*yComponents)
+
+	// Size Flag
+	str, err := base83.Encode((xComponents-1)+(yComponents-1)*9, 1)
+	if err != nil {
+		return "", EncodingError("could not encode size flag")
+	}
+	blurhash.WriteString(str)
+
+	factors := make([]float64, yComponents*xComponents*3)
+	multiplyBasisFunction(rgba, factors, xComponents, yComponents)
+
+	var maximumValue float64
+	var quantisedMaximumValue int
+	var acCount = xComponents*yComponents - 1
+	if acCount > 0 {
+		var actualMaximumValue float64
+		for i := 0; i < acCount*3; i++ {
+			actualMaximumValue = math.Max(math.Abs(factors[i+3]), actualMaximumValue)
+		}
+		quantisedMaximumValue = int(math.Max(0, math.Min(82, math.Floor(actualMaximumValue*166-0.5))))
+		maximumValue = (float64(quantisedMaximumValue) + 1) / 166
+	} else {
+		maximumValue = 1
+	}
+
+	// Quantised max AC component
+	str, err = base83.Encode(quantisedMaximumValue, 1)
+	if err != nil {
+		return "", EncodingError("could not encode quantised max AC component")
+	}
+	blurhash.WriteString(str)
+
+	// DC value
+	str, err = base83.Encode(encodeDC(factors[0], factors[1], factors[2]), 4)
+	if err != nil {
+		return "", EncodingError("could not encode DC value")
+	}
+	blurhash.WriteString(str)
+
+	// AC values
+	for i := 0; i < acCount; i++ {
+		str, err = base83.Encode(encodeAC(factors[3+(i*3+0)], factors[3+(i*3+1)], factors[3+(i*3+2)], maximumValue), 2)
+		if err != nil {
+			return "", EncodingError("could not encode AC value")
+		}
+		blurhash.WriteString(str)
+	}
+
+	if blurhash.Len() != 4+2*xComponents*yComponents {
+		return "", EncodingError("hash does not match expected size")
+	}
+
+	return blurhash.String(), nil
+}
+
+func multiplyBasisFunction(rgba image.Image, factors []float64, xComponents int, yComponents int) {
+	height := rgba.Bounds().Max.Y
+	width := rgba.Bounds().Max.X
+
+	xvalues := make([][]float64, xComponents)
+	for xComponent := 0; xComponent < xComponents; xComponent++ {
+		xvalues[xComponent] = make([]float64, width)
+		for x := 0; x < width; x++ {
+			xvalues[xComponent][x] = math.Cos(math.Pi * float64(xComponent) * float64(x) / float64(width))
+		}
+	}
+
+	yvalues := make([][]float64, yComponents)
+	for yComponent := 0; yComponent < yComponents; yComponent++ {
+		yvalues[yComponent] = make([]float64, height)
+		for y := 0; y < height; y++ {
+			yvalues[yComponent][y] = math.Cos(math.Pi * float64(yComponent) * float64(y) / float64(height))
+		}
+	}
+
+	for y := 0; y < height; y++ {
+		for x := 0; x < width; x++ {
+			rt, gt, bt, _ := rgba.At(x, y).RGBA()
+			lr := channelToLinear[rt>>8]
+			lg := channelToLinear[gt>>8]
+			lb := channelToLinear[bt>>8]
+
+			for yc := 0; yc < yComponents; yc++ {
+				for xc := 0; xc < xComponents; xc++ {
+
+					scale := 1 / float64(width*height)
+
+					if xc != 0 || yc != 0 {
+						scale = 2 / float64(width*height)
+					}
+
+					basis := xvalues[xc][x] * yvalues[yc][y]
+					factors[0+xc*3+yc*3*xComponents] += lr * basis * scale
+					factors[1+xc*3+yc*3*xComponents] += lg * basis * scale
+					factors[2+xc*3+yc*3*xComponents] += lb * basis * scale
+				}
+			}
+		}
+	}
+}
+
+func encodeDC(r, g, b float64) int {
+	return (linearTosRGB(r) << 16) + (linearTosRGB(g) << 8) + linearTosRGB(b)
+}
+
+func encodeAC(r, g, b, maximumValue float64) int {
+	quant := func(f float64) int {
+		return int(math.Max(0, math.Min(18, math.Floor(signPow(f/maximumValue, 0.5)*9+9.5))))
+	}
+	return quant(r)*19*19 + quant(g)*19 + quant(b)
+}