From 29e976bbb079e089f1391c1e42761e00c936b22c Mon Sep 17 00:00:00 2001
From: Lorenz Diener <ldiener@uni-bremen.de>
Date: Wed, 8 May 2019 18:45:24 +0200
Subject: [PATCH] This is just the javascript code, will port later

---
 blurhash.py | 90 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 90 insertions(+)
 create mode 100644 blurhash.py

diff --git a/blurhash.py b/blurhash.py
new file mode 100644
index 0000000..df950f9
--- /dev/null
+++ b/blurhash.py
@@ -0,0 +1,90 @@
+"""
+import { decode83 } from './base83';
+import { sRGBToLinear, signPow, linearTosRGB } from './utils';
+
+const decodeDC = (value: number) => {
+  const intR = value >> 16;
+  const intG = (value >> 8) & 255;
+  const intB = value & 255;
+  return [sRGBToLinear(intR), sRGBToLinear(intG), sRGBToLinear(intB)];
+};
+
+const decodeAC = (value: number, maximumValue: number) => {
+  const quantR = Math.floor(value / (19 * 19));
+  const quantG = Math.floor(value / 19) % 19;
+  const quantB = value % 19;
+
+  const rgb = [
+    signPow((quantR - 9) / 9, 2.0) * maximumValue,
+    signPow((quantG - 9) / 9, 2.0) * maximumValue,
+    signPow((quantB - 9) / 9, 2.0) * maximumValue,
+  ];
+
+  return rgb;
+};
+
+const decode = (blurhash: string, width: number, height: number, punch?: number) => {
+  punch = punch | 1;
+
+  if (blurhash.length < 6) {
+    console.error('too short blurhash');
+    return null;
+  }
+
+  const sizeFlag = decode83(blurhash[0]);
+  const numY = Math.floor(sizeFlag / 9) + 1;
+  const numX = (sizeFlag % 9) + 1;
+
+  const quantisedMaximumValue = decode83(blurhash[1]);
+  const maximumValue = (quantisedMaximumValue + 1) / 166;
+
+  if (blurhash.length !== 4 + 2 * numX * numY) {
+    console.error('blurhash length mismatch', blurhash.length, 4 + 2 * numX * numY);
+    return null;
+  }
+
+  const colors = new Array(numX * numY);
+  for (let i = 0; i < colors.length; i++) {
+    if (i === 0) {
+      const value = decode83(blurhash.substring(2, 6));
+      colors[i] = decodeDC(value);
+    } else {
+      const value = decode83(blurhash.substring(4 + i * 2, 6 + i * 2));
+      colors[i] = decodeAC(value, maximumValue * punch);
+    }
+  }
+
+  const bytesPerRow = width * 4;
+  const pixels = new Uint8ClampedArray(bytesPerRow * height);
+
+  for (let y = 0; y < height; y++) {
+    for (let x = 0; x < width; x++) {
+      let r = 0;
+      let g = 0;
+      let b = 0;
+
+      for (let j = 0; j < numY; j++) {
+        for (let i = 0; i < numX; i++) {
+          const basis = Math.cos(Math.PI * x * i / width) * Math.cos(Math.PI * y * j / height);
+          let color = colors[i + j * numX];
+          r += color[0] * basis;
+          g += color[1] * basis;
+          b += color[2] * basis;
+        }
+      }
+
+      let intR = linearTosRGB(r);
+      let intG = linearTosRGB(g);
+      let intB = linearTosRGB(b);
+
+      pixels[4 * x + 0 + y * bytesPerRow] = intR;
+      pixels[4 * x + 1 + y * bytesPerRow] = intG;
+      pixels[4 * x + 2 + y * bytesPerRow] = intB;
+      pixels[4 * x + 3 + y * bytesPerRow] = 255; // alpha
+    }
+  }
+  return pixels;
+};
+
+export default decode;
+"""