use web assembly and web worker for data decoder

apps/assets/coffee/decoder.1.coffee

@@ -0,0 +1,84 @@
+#zlib library
+importScripts('pako.min.js')
+# jpeg library
+importScripts('jpeg-decoder.js')
+resolution = undefined
+pixelValue = (value, depth) ->
+    pixel =
+        r: 255
+        g: 255
+        b: 255
+        a: 255
+    #console.log("len is" + arr.length)
+    if depth is 24 or depth is 32
+        pixel.r = value & 0xFF
+        pixel.g = (value >> 8) & 0xFF
+        pixel.b = (value >> 16) & 0xFF
+    else if depth is 16
+        pixel.r = (value & 0x1F) * (255 / 31)
+        pixel.g = ((value >> 5) & 0x3F) * (255 / 63)
+        pixel.b = ((value >> 11) & 0x1F) * (255 / 31)
+    #console.log pixel
+    return pixel
+
+getImageData = (d) ->
+    return d.pixels if resolution.depth is 32
+    step = resolution.depth / 8
+    npixels = d.pixels.length / step
+    data = new Uint8ClampedArray d.w * d.h * 4
+    for i in [0..npixels - 1]
+        value = 0
+        value = value | d.pixels[i * step + j] << (j * 8) for j in [0..step - 1]
+        pixel = pixelValue value, resolution.depth
+        data[i * 4] = pixel.r
+        data[i * 4 + 1] = pixel.g
+        data[i * 4 + 2] = pixel.b
+        data[i * 4 + 3] = pixel.a
+    return data
+
+decodeRaw = (d) ->
+    d.pixels = getImageData d
+    return d
+
+decodeJPEG = (d) ->
+    raw = decode d.pixels, { useTArray: true, colorTransform: true }
+    d.pixels = raw.data
+    return d
+    ###
+    blob = new Blob [d.pixels], { type: "image/jpeg" }
+    reader = new FileReader()
+    reader.onloadend = () ->
+        d.pixels = reader.result
+        postMessage d
+    reader.readAsDataURL blob
+    ###
+
+update = (msg) ->
+    d = {}
+    data = new Uint8Array msg
+    d.x = data[1] | (data[2]<<8)
+    d.y = data[3] | (data[4]<<8)
+    d.w = data[5] | (data[6]<<8)
+    d.h = data[7] | (data[8]<<8)
+    d.flag = data[9]
+    d.pixels = data.subarray 10
+    # the zlib is slower than expected
+    switch d.flag
+        when 0x0 # raw data
+            raw = decodeRaw d
+        when 0x1 # jpeg data
+            raw = decodeJPEG(d)
+        when 0x2 # raw compress in zlib format
+            d.pixels =  pako.inflate(d.pixels)
+            raw = decodeRaw d
+        when 0x3 # jpeg compress in zlib format
+            d.pixels = pako.inflate(d.pixels)
+            raw = decodeJPEG(d)
+    return unless raw
+    raw.pixels = raw.pixels.buffer
+    # fill the rectangle
+    postMessage raw, [raw.pixels]
+
+onmessage = (e) ->
+    return resolution = e.data if e.data.depth
+    update e.data