808 lines
31 KiB
JavaScript
808 lines
31 KiB
JavaScript
// (c) Dean McNamee <dean@gmail.com>, 2013.
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//
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// https://github.com/deanm/omggif
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//
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// Permission is hereby granted, free of charge, to any person obtaining a copy
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// of this software and associated documentation files (the "Software"), to
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// deal in the Software without restriction, including without limitation the
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// rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
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// sell copies of the Software, and to permit persons to whom the Software is
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// furnished to do so, subject to the following conditions:
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//
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// The above copyright notice and this permission notice shall be included in
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// all copies or substantial portions of the Software.
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//
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// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
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// IN THE SOFTWARE.
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//
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// omggif is a JavaScript implementation of a GIF 89a encoder and decoder,
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// including animation and compression. It does not rely on any specific
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// underlying system, so should run in the browser, Node, or Plask.
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"use strict";
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function GifWriter(buf, width, height, gopts) {
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var p = 0;
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var gopts = gopts === undefined ? { } : gopts;
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var loop_count = gopts.loop === undefined ? null : gopts.loop;
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var global_palette = gopts.palette === undefined ? null : gopts.palette;
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if (width <= 0 || height <= 0 || width > 65535 || height > 65535)
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throw new Error("Width/Height invalid.");
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function check_palette_and_num_colors(palette) {
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var num_colors = palette.length;
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if (num_colors < 2 || num_colors > 256 || num_colors & (num_colors-1)) {
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throw new Error(
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"Invalid code/color length, must be power of 2 and 2 .. 256.");
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}
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return num_colors;
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}
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// - Header.
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buf[p++] = 0x47; buf[p++] = 0x49; buf[p++] = 0x46; // GIF
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buf[p++] = 0x38; buf[p++] = 0x39; buf[p++] = 0x61; // 89a
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// Handling of Global Color Table (palette) and background index.
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var gp_num_colors_pow2 = 0;
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var background = 0;
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if (global_palette !== null) {
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var gp_num_colors = check_palette_and_num_colors(global_palette);
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while (gp_num_colors >>= 1) ++gp_num_colors_pow2;
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gp_num_colors = 1 << gp_num_colors_pow2;
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--gp_num_colors_pow2;
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if (gopts.background !== undefined) {
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background = gopts.background;
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if (background >= gp_num_colors)
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throw new Error("Background index out of range.");
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// The GIF spec states that a background index of 0 should be ignored, so
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// this is probably a mistake and you really want to set it to another
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// slot in the palette. But actually in the end most browsers, etc end
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// up ignoring this almost completely (including for dispose background).
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if (background === 0)
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throw new Error("Background index explicitly passed as 0.");
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}
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}
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// - Logical Screen Descriptor.
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// NOTE(deanm): w/h apparently ignored by implementations, but set anyway.
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buf[p++] = width & 0xff; buf[p++] = width >> 8 & 0xff;
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buf[p++] = height & 0xff; buf[p++] = height >> 8 & 0xff;
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// NOTE: Indicates 0-bpp original color resolution (unused?).
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buf[p++] = (global_palette !== null ? 0x80 : 0) | // Global Color Table Flag.
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gp_num_colors_pow2; // NOTE: No sort flag (unused?).
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buf[p++] = background; // Background Color Index.
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buf[p++] = 0; // Pixel aspect ratio (unused?).
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// - Global Color Table
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if (global_palette !== null) {
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for (var i = 0, il = global_palette.length; i < il; ++i) {
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var rgb = global_palette[i];
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buf[p++] = rgb >> 16 & 0xff;
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buf[p++] = rgb >> 8 & 0xff;
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buf[p++] = rgb & 0xff;
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}
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}
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if (loop_count !== null) { // Netscape block for looping.
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if (loop_count < 0 || loop_count > 65535)
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throw new Error("Loop count invalid.")
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// Extension code, label, and length.
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buf[p++] = 0x21; buf[p++] = 0xff; buf[p++] = 0x0b;
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// NETSCAPE2.0
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buf[p++] = 0x4e; buf[p++] = 0x45; buf[p++] = 0x54; buf[p++] = 0x53;
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buf[p++] = 0x43; buf[p++] = 0x41; buf[p++] = 0x50; buf[p++] = 0x45;
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buf[p++] = 0x32; buf[p++] = 0x2e; buf[p++] = 0x30;
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// Sub-block
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buf[p++] = 0x03; buf[p++] = 0x01;
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buf[p++] = loop_count & 0xff; buf[p++] = loop_count >> 8 & 0xff;
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buf[p++] = 0x00; // Terminator.
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}
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var ended = false;
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this.addFrame = function(x, y, w, h, indexed_pixels, opts) {
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if (ended === true) { --p; ended = false; } // Un-end.
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opts = opts === undefined ? { } : opts;
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// TODO(deanm): Bounds check x, y. Do they need to be within the virtual
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// canvas width/height, I imagine?
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if (x < 0 || y < 0 || x > 65535 || y > 65535)
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throw new Error("x/y invalid.")
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if (w <= 0 || h <= 0 || w > 65535 || h > 65535)
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throw new Error("Width/Height invalid.")
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if (indexed_pixels.length < w * h)
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throw new Error("Not enough pixels for the frame size.");
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var using_local_palette = true;
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var palette = opts.palette;
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if (palette === undefined || palette === null) {
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using_local_palette = false;
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palette = global_palette;
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}
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if (palette === undefined || palette === null)
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throw new Error("Must supply either a local or global palette.");
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var num_colors = check_palette_and_num_colors(palette);
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// Compute the min_code_size (power of 2), destroying num_colors.
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var min_code_size = 0;
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while (num_colors >>= 1) ++min_code_size;
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num_colors = 1 << min_code_size; // Now we can easily get it back.
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var delay = opts.delay === undefined ? 0 : opts.delay;
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// From the spec:
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// 0 - No disposal specified. The decoder is
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// not required to take any action.
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// 1 - Do not dispose. The graphic is to be left
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// in place.
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// 2 - Restore to background color. The area used by the
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// graphic must be restored to the background color.
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// 3 - Restore to previous. The decoder is required to
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// restore the area overwritten by the graphic with
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// what was there prior to rendering the graphic.
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// 4-7 - To be defined.
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// NOTE(deanm): Dispose background doesn't really work, apparently most
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// browsers ignore the background palette index and clear to transparency.
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var disposal = opts.disposal === undefined ? 0 : opts.disposal;
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if (disposal < 0 || disposal > 3) // 4-7 is reserved.
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throw new Error("Disposal out of range.");
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var use_transparency = false;
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var transparent_index = 0;
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if (opts.transparent !== undefined && opts.transparent !== null) {
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use_transparency = true;
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transparent_index = opts.transparent;
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if (transparent_index < 0 || transparent_index >= num_colors)
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throw new Error("Transparent color index.");
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}
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if (disposal !== 0 || use_transparency || delay !== 0) {
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// - Graphics Control Extension
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buf[p++] = 0x21; buf[p++] = 0xf9; // Extension / Label.
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buf[p++] = 4; // Byte size.
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buf[p++] = disposal << 2 | (use_transparency === true ? 1 : 0);
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buf[p++] = delay & 0xff; buf[p++] = delay >> 8 & 0xff;
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buf[p++] = transparent_index; // Transparent color index.
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buf[p++] = 0; // Block Terminator.
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}
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// - Image Descriptor
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buf[p++] = 0x2c; // Image Seperator.
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buf[p++] = x & 0xff; buf[p++] = x >> 8 & 0xff; // Left.
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buf[p++] = y & 0xff; buf[p++] = y >> 8 & 0xff; // Top.
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buf[p++] = w & 0xff; buf[p++] = w >> 8 & 0xff;
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buf[p++] = h & 0xff; buf[p++] = h >> 8 & 0xff;
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// NOTE: No sort flag (unused?).
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// TODO(deanm): Support interlace.
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buf[p++] = using_local_palette === true ? (0x80 | (min_code_size-1)) : 0;
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// - Local Color Table
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if (using_local_palette === true) {
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for (var i = 0, il = palette.length; i < il; ++i) {
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var rgb = palette[i];
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buf[p++] = rgb >> 16 & 0xff;
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buf[p++] = rgb >> 8 & 0xff;
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buf[p++] = rgb & 0xff;
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}
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}
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p = GifWriterOutputLZWCodeStream(
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buf, p, min_code_size < 2 ? 2 : min_code_size, indexed_pixels);
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return p;
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};
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this.end = function() {
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if (ended === false) {
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buf[p++] = 0x3b; // Trailer.
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ended = true;
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}
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return p;
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};
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this.getOutputBuffer = function() { return buf; };
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this.setOutputBuffer = function(v) { buf = v; };
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this.getOutputBufferPosition = function() { return p; };
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this.setOutputBufferPosition = function(v) { p = v; };
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}
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// Main compression routine, palette indexes -> LZW code stream.
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// |index_stream| must have at least one entry.
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function GifWriterOutputLZWCodeStream(buf, p, min_code_size, index_stream) {
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buf[p++] = min_code_size;
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var cur_subblock = p++; // Pointing at the length field.
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var clear_code = 1 << min_code_size;
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var code_mask = clear_code - 1;
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var eoi_code = clear_code + 1;
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var next_code = eoi_code + 1;
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var cur_code_size = min_code_size + 1; // Number of bits per code.
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var cur_shift = 0;
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// We have at most 12-bit codes, so we should have to hold a max of 19
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// bits here (and then we would write out).
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var cur = 0;
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function emit_bytes_to_buffer(bit_block_size) {
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while (cur_shift >= bit_block_size) {
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buf[p++] = cur & 0xff;
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cur >>= 8; cur_shift -= 8;
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if (p === cur_subblock + 256) { // Finished a subblock.
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buf[cur_subblock] = 255;
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cur_subblock = p++;
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}
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}
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}
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function emit_code(c) {
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cur |= c << cur_shift;
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cur_shift += cur_code_size;
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emit_bytes_to_buffer(8);
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}
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// I am not an expert on the topic, and I don't want to write a thesis.
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// However, it is good to outline here the basic algorithm and the few data
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// structures and optimizations here that make this implementation fast.
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// The basic idea behind LZW is to build a table of previously seen runs
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// addressed by a short id (herein called output code). All data is
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// referenced by a code, which represents one or more values from the
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// original input stream. All input bytes can be referenced as the same
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// value as an output code. So if you didn't want any compression, you
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// could more or less just output the original bytes as codes (there are
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// some details to this, but it is the idea). In order to achieve
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// compression, values greater then the input range (codes can be up to
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// 12-bit while input only 8-bit) represent a sequence of previously seen
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// inputs. The decompressor is able to build the same mapping while
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// decoding, so there is always a shared common knowledge between the
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// encoding and decoder, which is also important for "timing" aspects like
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// how to handle variable bit width code encoding.
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//
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// One obvious but very important consequence of the table system is there
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// is always a unique id (at most 12-bits) to map the runs. 'A' might be
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// 4, then 'AA' might be 10, 'AAA' 11, 'AAAA' 12, etc. This relationship
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// can be used for an effecient lookup strategy for the code mapping. We
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// need to know if a run has been seen before, and be able to map that run
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// to the output code. Since we start with known unique ids (input bytes),
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// and then from those build more unique ids (table entries), we can
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// continue this chain (almost like a linked list) to always have small
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// integer values that represent the current byte chains in the encoder.
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// This means instead of tracking the input bytes (AAAABCD) to know our
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// current state, we can track the table entry for AAAABC (it is guaranteed
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// to exist by the nature of the algorithm) and the next character D.
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// Therefor the tuple of (table_entry, byte) is guaranteed to also be
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// unique. This allows us to create a simple lookup key for mapping input
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// sequences to codes (table indices) without having to store or search
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// any of the code sequences. So if 'AAAA' has a table entry of 12, the
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// tuple of ('AAAA', K) for any input byte K will be unique, and can be our
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// key. This leads to a integer value at most 20-bits, which can always
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// fit in an SMI value and be used as a fast sparse array / object key.
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// Output code for the current contents of the index buffer.
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var ib_code = index_stream[0] & code_mask; // Load first input index.
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var code_table = { }; // Key'd on our 20-bit "tuple".
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emit_code(clear_code); // Spec says first code should be a clear code.
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// First index already loaded, process the rest of the stream.
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for (var i = 1, il = index_stream.length; i < il; ++i) {
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var k = index_stream[i] & code_mask;
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var cur_key = ib_code << 8 | k; // (prev, k) unique tuple.
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var cur_code = code_table[cur_key]; // buffer + k.
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// Check if we have to create a new code table entry.
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if (cur_code === undefined) { // We don't have buffer + k.
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// Emit index buffer (without k).
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// This is an inline version of emit_code, because this is the core
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// writing routine of the compressor (and V8 cannot inline emit_code
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// because it is a closure here in a different context). Additionally
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// we can call emit_byte_to_buffer less often, because we can have
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// 30-bits (from our 31-bit signed SMI), and we know our codes will only
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// be 12-bits, so can safely have 18-bits there without overflow.
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// emit_code(ib_code);
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cur |= ib_code << cur_shift;
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cur_shift += cur_code_size;
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while (cur_shift >= 8) {
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buf[p++] = cur & 0xff;
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cur >>= 8; cur_shift -= 8;
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if (p === cur_subblock + 256) { // Finished a subblock.
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buf[cur_subblock] = 255;
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cur_subblock = p++;
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}
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}
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if (next_code === 4096) { // Table full, need a clear.
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emit_code(clear_code);
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next_code = eoi_code + 1;
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cur_code_size = min_code_size + 1;
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code_table = { };
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} else { // Table not full, insert a new entry.
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// Increase our variable bit code sizes if necessary. This is a bit
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// tricky as it is based on "timing" between the encoding and
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// decoder. From the encoders perspective this should happen after
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// we've already emitted the index buffer and are about to create the
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// first table entry that would overflow our current code bit size.
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if (next_code >= (1 << cur_code_size)) ++cur_code_size;
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code_table[cur_key] = next_code++; // Insert into code table.
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}
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ib_code = k; // Index buffer to single input k.
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} else {
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ib_code = cur_code; // Index buffer to sequence in code table.
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}
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}
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emit_code(ib_code); // There will still be something in the index buffer.
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emit_code(eoi_code); // End Of Information.
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// Flush / finalize the sub-blocks stream to the buffer.
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emit_bytes_to_buffer(1);
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// Finish the sub-blocks, writing out any unfinished lengths and
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// terminating with a sub-block of length 0. If we have already started
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// but not yet used a sub-block it can just become the terminator.
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if (cur_subblock + 1 === p) { // Started but unused.
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buf[cur_subblock] = 0;
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} else { // Started and used, write length and additional terminator block.
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buf[cur_subblock] = p - cur_subblock - 1;
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buf[p++] = 0;
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}
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return p;
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}
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function GifReader(buf) {
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var p = 0;
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// - Header (GIF87a or GIF89a).
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if (buf[p++] !== 0x47 || buf[p++] !== 0x49 || buf[p++] !== 0x46 ||
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buf[p++] !== 0x38 || (buf[p++]+1 & 0xfd) !== 0x38 || buf[p++] !== 0x61) {
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throw new Error("Invalid GIF 87a/89a header.");
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}
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// - Logical Screen Descriptor.
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var width = buf[p++] | buf[p++] << 8;
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var height = buf[p++] | buf[p++] << 8;
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var pf0 = buf[p++]; // <Packed Fields>.
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var global_palette_flag = pf0 >> 7;
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var num_global_colors_pow2 = pf0 & 0x7;
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var num_global_colors = 1 << (num_global_colors_pow2 + 1);
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var background = buf[p++];
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buf[p++]; // Pixel aspect ratio (unused?).
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var global_palette_offset = null;
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var global_palette_size = null;
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if (global_palette_flag) {
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global_palette_offset = p;
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global_palette_size = num_global_colors;
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p += num_global_colors * 3; // Seek past palette.
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}
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var no_eof = true;
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var frames = [ ];
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var delay = 0;
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var transparent_index = null;
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var disposal = 0; // 0 - No disposal specified.
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var loop_count = null;
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this.width = width;
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this.height = height;
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while (no_eof && p < buf.length) {
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switch (buf[p++]) {
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case 0x21: // Graphics Control Extension Block
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switch (buf[p++]) {
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case 0xff: // Application specific block
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// Try if it's a Netscape block (with animation loop counter).
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if (buf[p ] !== 0x0b || // 21 FF already read, check block size.
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// NETSCAPE2.0
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buf[p+1 ] == 0x4e && buf[p+2 ] == 0x45 && buf[p+3 ] == 0x54 &&
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buf[p+4 ] == 0x53 && buf[p+5 ] == 0x43 && buf[p+6 ] == 0x41 &&
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buf[p+7 ] == 0x50 && buf[p+8 ] == 0x45 && buf[p+9 ] == 0x32 &&
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buf[p+10] == 0x2e && buf[p+11] == 0x30 &&
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// Sub-block
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buf[p+12] == 0x03 && buf[p+13] == 0x01 && buf[p+16] == 0) {
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p += 14;
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loop_count = buf[p++] | buf[p++] << 8;
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p++; // Skip terminator.
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} else { // We don't know what it is, just try to get past it.
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p += 12;
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while (true) { // Seek through subblocks.
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var block_size = buf[p++];
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// Bad block size (ex: undefined from an out of bounds read).
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if (!(block_size >= 0)) throw Error("Invalid block size");
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if (block_size === 0) break; // 0 size is terminator
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p += block_size;
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}
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}
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break;
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|
|
case 0xf9: // Graphics Control Extension
|
|
if (buf[p++] !== 0x4 || buf[p+4] !== 0)
|
|
throw new Error("Invalid graphics extension block.");
|
|
var pf1 = buf[p++];
|
|
delay = buf[p++] | buf[p++] << 8;
|
|
transparent_index = buf[p++];
|
|
if ((pf1 & 1) === 0) transparent_index = null;
|
|
disposal = pf1 >> 2 & 0x7;
|
|
p++; // Skip terminator.
|
|
break;
|
|
|
|
case 0xfe: // Comment Extension.
|
|
while (true) { // Seek through subblocks.
|
|
var block_size = buf[p++];
|
|
// Bad block size (ex: undefined from an out of bounds read).
|
|
if (!(block_size >= 0)) throw Error("Invalid block size");
|
|
if (block_size === 0) break; // 0 size is terminator
|
|
// console.log(buf.slice(p, p+block_size).toString('ascii'));
|
|
p += block_size;
|
|
}
|
|
break;
|
|
|
|
default:
|
|
throw new Error(
|
|
"Unknown graphic control label: 0x" + buf[p-1].toString(16));
|
|
}
|
|
break;
|
|
|
|
case 0x2c: // Image Descriptor.
|
|
var x = buf[p++] | buf[p++] << 8;
|
|
var y = buf[p++] | buf[p++] << 8;
|
|
var w = buf[p++] | buf[p++] << 8;
|
|
var h = buf[p++] | buf[p++] << 8;
|
|
var pf2 = buf[p++];
|
|
var local_palette_flag = pf2 >> 7;
|
|
var interlace_flag = pf2 >> 6 & 1;
|
|
var num_local_colors_pow2 = pf2 & 0x7;
|
|
var num_local_colors = 1 << (num_local_colors_pow2 + 1);
|
|
var palette_offset = global_palette_offset;
|
|
var palette_size = global_palette_size;
|
|
var has_local_palette = false;
|
|
if (local_palette_flag) {
|
|
var has_local_palette = true;
|
|
palette_offset = p; // Override with local palette.
|
|
palette_size = num_local_colors;
|
|
p += num_local_colors * 3; // Seek past palette.
|
|
}
|
|
|
|
var data_offset = p;
|
|
|
|
p++; // codesize
|
|
while (true) {
|
|
var block_size = buf[p++];
|
|
// Bad block size (ex: undefined from an out of bounds read).
|
|
if (!(block_size >= 0)) throw Error("Invalid block size");
|
|
if (block_size === 0) break; // 0 size is terminator
|
|
p += block_size;
|
|
}
|
|
|
|
frames.push({x: x, y: y, width: w, height: h,
|
|
has_local_palette: has_local_palette,
|
|
palette_offset: palette_offset,
|
|
palette_size: palette_size,
|
|
data_offset: data_offset,
|
|
data_length: p - data_offset,
|
|
transparent_index: transparent_index,
|
|
interlaced: !!interlace_flag,
|
|
delay: delay,
|
|
disposal: disposal});
|
|
break;
|
|
|
|
case 0x3b: // Trailer Marker (end of file).
|
|
no_eof = false;
|
|
break;
|
|
|
|
default:
|
|
throw new Error("Unknown gif block: 0x" + buf[p-1].toString(16));
|
|
break;
|
|
}
|
|
}
|
|
|
|
this.numFrames = function() {
|
|
return frames.length;
|
|
};
|
|
|
|
this.loopCount = function() {
|
|
return loop_count;
|
|
};
|
|
|
|
this.frameInfo = function(frame_num) {
|
|
if (frame_num < 0 || frame_num >= frames.length)
|
|
throw new Error("Frame index out of range.");
|
|
return frames[frame_num];
|
|
}
|
|
|
|
this.decodeAndBlitFrameBGRA = function(frame_num, pixels) {
|
|
var frame = this.frameInfo(frame_num);
|
|
var num_pixels = frame.width * frame.height;
|
|
var index_stream = new Uint8Array(num_pixels); // At most 8-bit indices.
|
|
GifReaderLZWOutputIndexStream(
|
|
buf, frame.data_offset, index_stream, num_pixels);
|
|
var palette_offset = frame.palette_offset;
|
|
|
|
// NOTE(deanm): It seems to be much faster to compare index to 256 than
|
|
// to === null. Not sure why, but CompareStub_EQ_STRICT shows up high in
|
|
// the profile, not sure if it's related to using a Uint8Array.
|
|
var trans = frame.transparent_index;
|
|
if (trans === null) trans = 256;
|
|
|
|
// We are possibly just blitting to a portion of the entire frame.
|
|
// That is a subrect within the framerect, so the additional pixels
|
|
// must be skipped over after we finished a scanline.
|
|
var framewidth = frame.width;
|
|
var framestride = width - framewidth;
|
|
var xleft = framewidth; // Number of subrect pixels left in scanline.
|
|
|
|
// Output indicies of the top left and bottom right corners of the subrect.
|
|
var opbeg = ((frame.y * width) + frame.x) * 4;
|
|
var opend = ((frame.y + frame.height) * width + frame.x) * 4;
|
|
var op = opbeg;
|
|
|
|
var scanstride = framestride * 4;
|
|
|
|
// Use scanstride to skip past the rows when interlacing. This is skipping
|
|
// 7 rows for the first two passes, then 3 then 1.
|
|
if (frame.interlaced === true) {
|
|
scanstride += width * 4 * 7; // Pass 1.
|
|
}
|
|
|
|
var interlaceskip = 8; // Tracking the row interval in the current pass.
|
|
|
|
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 (op >= opend) { // Catch the wrap to switch passes when interlacing.
|
|
scanstride = framestride * 4 + width * 4 * (interlaceskip-1);
|
|
// interlaceskip / 2 * 4 is interlaceskip << 1.
|
|
op = opbeg + (framewidth + framestride) * (interlaceskip << 1);
|
|
interlaceskip >>= 1;
|
|
}
|
|
}
|
|
|
|
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++] = b;
|
|
pixels[op++] = g;
|
|
pixels[op++] = r;
|
|
pixels[op++] = 255;
|
|
}
|
|
--xleft;
|
|
}
|
|
};
|
|
|
|
// I will go to copy and paste hell one day...
|
|
this.decodeAndBlitFrameRGBA = function(frame_num, pixels) {
|
|
var frame = this.frameInfo(frame_num);
|
|
var num_pixels = frame.width * frame.height;
|
|
var index_stream = new Uint8Array(num_pixels); // At most 8-bit indices.
|
|
GifReaderLZWOutputIndexStream(
|
|
buf, frame.data_offset, index_stream, num_pixels);
|
|
var palette_offset = frame.palette_offset;
|
|
|
|
// NOTE(deanm): It seems to be much faster to compare index to 256 than
|
|
// to === null. Not sure why, but CompareStub_EQ_STRICT shows up high in
|
|
// the profile, not sure if it's related to using a Uint8Array.
|
|
var trans = frame.transparent_index;
|
|
if (trans === null) trans = 256;
|
|
|
|
// We are possibly just blitting to a portion of the entire frame.
|
|
// That is a subrect within the framerect, so the additional pixels
|
|
// must be skipped over after we finished a scanline.
|
|
var framewidth = frame.width;
|
|
var framestride = width - framewidth;
|
|
var xleft = framewidth; // Number of subrect pixels left in scanline.
|
|
|
|
// Output indicies of the top left and bottom right corners of the subrect.
|
|
var opbeg = ((frame.y * width) + frame.x) * 4;
|
|
var opend = ((frame.y + frame.height) * width + frame.x) * 4;
|
|
var op = opbeg;
|
|
|
|
var scanstride = framestride * 4;
|
|
|
|
// Use scanstride to skip past the rows when interlacing. This is skipping
|
|
// 7 rows for the first two passes, then 3 then 1.
|
|
if (frame.interlaced === true) {
|
|
scanstride += width * 4 * 7; // Pass 1.
|
|
}
|
|
|
|
var interlaceskip = 8; // Tracking the row interval in the current pass.
|
|
|
|
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 (op >= opend) { // Catch the wrap to switch passes when interlacing.
|
|
scanstride = framestride * 4 + width * 4 * (interlaceskip-1);
|
|
// interlaceskip / 2 * 4 is interlaceskip << 1.
|
|
op = opbeg + (framewidth + framestride) * (interlaceskip << 1);
|
|
interlaceskip >>= 1;
|
|
}
|
|
}
|
|
|
|
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;
|
|
}
|
|
};
|
|
}
|
|
|
|
function GifReaderLZWOutputIndexStream(code_stream, p, output, output_length) {
|
|
var min_code_size = code_stream[p++];
|
|
|
|
var clear_code = 1 << min_code_size;
|
|
var eoi_code = clear_code + 1;
|
|
var next_code = eoi_code + 1;
|
|
|
|
var cur_code_size = min_code_size + 1; // Number of bits per code.
|
|
// NOTE: This shares the same name as the encoder, but has a different
|
|
// meaning here. Here this masks each code coming from the code stream.
|
|
var code_mask = (1 << cur_code_size) - 1;
|
|
var cur_shift = 0;
|
|
var cur = 0;
|
|
|
|
var op = 0; // Output pointer.
|
|
|
|
var subblock_size = code_stream[p++];
|
|
|
|
// TODO(deanm): Would using a TypedArray be any faster? At least it would
|
|
// solve the fast mode / backing store uncertainty.
|
|
// var code_table = Array(4096);
|
|
var code_table = new Int32Array(4096); // Can be signed, we only use 20 bits.
|
|
|
|
var prev_code = null; // Track code-1.
|
|
|
|
while (true) {
|
|
// Read up to two bytes, making sure we always 12-bits for max sized code.
|
|
while (cur_shift < 16) {
|
|
if (subblock_size === 0) break; // No more data to be read.
|
|
|
|
cur |= code_stream[p++] << cur_shift;
|
|
cur_shift += 8;
|
|
|
|
if (subblock_size === 1) { // Never let it get to 0 to hold logic above.
|
|
subblock_size = code_stream[p++]; // Next subblock.
|
|
} else {
|
|
--subblock_size;
|
|
}
|
|
}
|
|
|
|
// TODO(deanm): We should never really get here, we should have received
|
|
// and EOI.
|
|
if (cur_shift < cur_code_size)
|
|
break;
|
|
|
|
var code = cur & code_mask;
|
|
cur >>= cur_code_size;
|
|
cur_shift -= cur_code_size;
|
|
|
|
// TODO(deanm): Maybe should check that the first code was a clear code,
|
|
// at least this is what you're supposed to do. But actually our encoder
|
|
// now doesn't emit a clear code first anyway.
|
|
if (code === clear_code) {
|
|
// We don't actually have to clear the table. This could be a good idea
|
|
// for greater error checking, but we don't really do any anyway. We
|
|
// will just track it with next_code and overwrite old entries.
|
|
|
|
next_code = eoi_code + 1;
|
|
cur_code_size = min_code_size + 1;
|
|
code_mask = (1 << cur_code_size) - 1;
|
|
|
|
// Don't update prev_code ?
|
|
prev_code = null;
|
|
continue;
|
|
} else if (code === eoi_code) {
|
|
break;
|
|
}
|
|
|
|
// We have a similar situation as the decoder, where we want to store
|
|
// variable length entries (code table entries), but we want to do in a
|
|
// faster manner than an array of arrays. The code below stores sort of a
|
|
// linked list within the code table, and then "chases" through it to
|
|
// construct the dictionary entries. When a new entry is created, just the
|
|
// last byte is stored, and the rest (prefix) of the entry is only
|
|
// referenced by its table entry. Then the code chases through the
|
|
// prefixes until it reaches a single byte code. We have to chase twice,
|
|
// first to compute the length, and then to actually copy the data to the
|
|
// output (backwards, since we know the length). The alternative would be
|
|
// storing something in an intermediate stack, but that doesn't make any
|
|
// more sense. I implemented an approach where it also stored the length
|
|
// in the code table, although it's a bit tricky because you run out of
|
|
// bits (12 + 12 + 8), but I didn't measure much improvements (the table
|
|
// entries are generally not the long). Even when I created benchmarks for
|
|
// very long table entries the complexity did not seem worth it.
|
|
// The code table stores the prefix entry in 12 bits and then the suffix
|
|
// byte in 8 bits, so each entry is 20 bits.
|
|
|
|
var chase_code = code < next_code ? code : prev_code;
|
|
|
|
// Chase what we will output, either {CODE} or {CODE-1}.
|
|
var chase_length = 0;
|
|
var chase = chase_code;
|
|
while (chase > clear_code) {
|
|
chase = code_table[chase] >> 8;
|
|
++chase_length;
|
|
}
|
|
|
|
var k = chase;
|
|
|
|
var op_end = op + chase_length + (chase_code !== code ? 1 : 0);
|
|
if (op_end > output_length) {
|
|
console.log("Warning, gif stream longer than expected.");
|
|
return;
|
|
}
|
|
|
|
// Already have the first byte from the chase, might as well write it fast.
|
|
output[op++] = k;
|
|
|
|
op += chase_length;
|
|
var b = op; // Track pointer, writing backwards.
|
|
|
|
if (chase_code !== code) // The case of emitting {CODE-1} + k.
|
|
output[op++] = k;
|
|
|
|
chase = chase_code;
|
|
while (chase_length--) {
|
|
chase = code_table[chase];
|
|
output[--b] = chase & 0xff; // Write backwards.
|
|
chase >>= 8; // Pull down to the prefix code.
|
|
}
|
|
|
|
if (prev_code !== null && next_code < 4096) {
|
|
code_table[next_code++] = prev_code << 8 | k;
|
|
// TODO(deanm): Figure out this clearing vs code growth logic better. I
|
|
// have an feeling that it should just happen somewhere else, for now it
|
|
// is awkward between when we grow past the max and then hit a clear code.
|
|
// For now just check if we hit the max 12-bits (then a clear code should
|
|
// follow, also of course encoded in 12-bits).
|
|
if (next_code >= code_mask+1 && cur_code_size < 12) {
|
|
++cur_code_size;
|
|
code_mask = code_mask << 1 | 1;
|
|
}
|
|
}
|
|
|
|
prev_code = code;
|
|
}
|
|
|
|
if (op !== output_length) {
|
|
console.log("Warning, gif stream shorter than expected.");
|
|
}
|
|
|
|
return output;
|
|
}
|
|
|
|
// CommonJS.
|
|
try { exports.GifWriter = GifWriter; exports.GifReader = GifReader } catch(e) {}
|