glif.js is a fork of omggif that speeds up gif decoding using WebGL.
For those using bower
$ bower install glif.jsvar gr = new GifReader(byteArray);
var glif = new GLIF(canvas);
gr.decodeAndGLIF(frame_num, glif);byteArrayis aUint8Arraycontaining the data to be decoded.canvasis aHTMLCanvasElementwhere the gif will be displayed.frame_numis the frame to display
Use viewer.js to help animate the gif.
var view = viewer(canvas, data, callback);
var timeoutID = view(false);canvasis aHTMLCanvasElementwhere the gif will be displayed.datais one ofArrayBuffer,Uint8Array, orGifReader(fromomggif).callbackis a function that is called after each frame is drawn. One parameter is passed - thetimeoutIDof thesetTimeout()call.clearTimeout(timeoutId)will stop the animation.
viewer returns a function (view) to draw the next frame of the gif. The function takes one argument, once. If once is true, then only one frame is drawn. The function returns the timeoutID of the first frame.
GIF decoding is slow because LZW decompression must be performed serially. But the next step, mapping palette indices to RGB colors, is easily parallelizable by the GPU.
More specifically, it turns this slow for loop:
for (var i = 0, il = index_stream.length; i < il; ++i) {
var index = index_stream[i];
if (xleft === 0) { // Beginning of new scan line
op += scanstride;
xleft = framewidth;
}
if (index === trans) {
op += 4;
} else {
var r = buf[palette_offset + index * 3];
var g = buf[palette_offset + index * 3 + 1];
var b = buf[palette_offset + index * 3 + 2];
pixels[op++] = r;
pixels[op++] = g;
pixels[op++] = b;
pixels[op++] = 255;
}
--xleft;
}into this fragment shader:
varying highp vec2 vTextureCoord;
uniform sampler2D uIndexStream;
uniform sampler2D uPalette;
uniform bool uTransparency;
uniform mediump float uTransparent;
void main(void) {
mediump float uIndex = texture2D(uIndexStream, vTextureCoord).r;
if (uTransparency && uIndex == uTransparent) {
gl_FragColor = vec4(0.0, 0.0, 0.0, 0.0);
} else {
gl_FragColor = texture2D(uPalette, vec2(uIndex, 0.5));
}
}(c) Dean McNamee <[email protected]>, 2013.
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to
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rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
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furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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