fix: 动作详情GIF动图播放 + 收藏按钮避让胶囊

miniprogram/components/gif-player/gif-player.js

@@ -0,0 +1,83 @@
+// gif-player：微信 <image> 组件不播放 GIF 动画（只渲染首帧），
+// 这里用 Canvas 2D + 纯 JS 解码器(omggif)逐帧绘制，实现真正的动图播放。
+const { GifReader } = require('../../utils/vendor/omggif.js');
+
+Component({
+  properties: {
+    // GIF 地址（通常是 ex.gifUrl，原始 180px 动图）
+    src: { type: String, value: '' }
+  },
+  data: {
+    failed: false
+  },
+  lifetimes: {
+    attached() {
+      this._aborted = false;
+      this._timer = null;
+      if (this.data.src) this._load();
+    },
+    detached() {
+      this._aborted = true;
+      if (this._timer) { clearTimeout(this._timer); this._timer = null; }
+    }
+  },
+  methods: {
+    _load() {
+      const src = this.data.src;
+      if (!src) return;
+      wx.request({
+        url: src,
+        responseType: 'arraybuffer',
+        success: (res) => {
+          if (this._aborted) return;
+          try {
+            this._play(res.data);
+          } catch (e) {
+            console.error('[gif-player] decode fail', e);
+            this.setData({ failed: true });
+          }
+        },
+        fail: () => {
+          if (!this._aborted) this.setData({ failed: true });
+        }
+      });
+    },
+    _play(buffer) {
+      const bytes = buffer instanceof ArrayBuffer ? new Uint8Array(buffer) : new Uint8Array(buffer);
+      const reader = new GifReader(bytes);
+      const numFrames = reader.numFrames();
+      if (!numFrames) { this.setData({ failed: true }); return; }
+      const w = reader.width;
+      const h = reader.height;
+      const q = wx.createSelectorQuery().in(this);
+      q.select('#gifCanvas').fields({ node: true, size: true }).exec((rs) => {
+        if (this._aborted || !rs || !rs[0] || !rs[0].node) return;
+        const canvas = rs[0].node;
+        const ctx = canvas.getContext('2d');
+        // 画布内部分辨率=GIF 原始分辨率；CSS 负责缩放到容器
+        canvas.width = w;
+        canvas.height = h;
+        const rgba = new Uint8ClampedArray(w * h * 4);
+        let frame = 0;
+        const render = () => {
+          if (this._aborted) return;
+          try {
+            // decodeAndBlitFrameRGBA 会按 GIF 的 disposal 规则在 rgba 上累积绘制
+            reader.decodeAndBlitFrameRGBA(frame, rgba);
+            const img = ctx.createImageData(w, h);
+            img.data.set(rgba);
+            ctx.putImageData(img, 0, 0);
+          } catch (e) {
+            console.error('[gif-player] frame fail', e);
+            return;
+          }
+          const info = reader.frameInfo(frame);
+          const delay = info && info.delay ? info.delay : 100;
+          frame = (frame + 1) % numFrames;
+          this._timer = setTimeout(render, Math.max(16, delay));
+        };
+        render();
+      });
+    }
+  }
+});

miniprogram/components/gif-player/gif-player.json

@@ -0,0 +1,4 @@
+{
+  "component": true,
+  "usingComponents": {}
+}

miniprogram/components/gif-player/gif-player.wxml

@@ -0,0 +1,3 @@
+<view class="gif-player">
+  <canvas type="2d" id="gifCanvas" class="canvas"></canvas>
+</view>

miniprogram/components/gif-player/gif-player.wxss

@@ -0,0 +1,2 @@
+.gif-player { width: 100%; height: 100%; }
+.canvas { width: 100%; height: 100%; display: block; }

miniprogram/pages/detail/detail.js

@@ -7,10 +7,13 @@ const auth = require('../../utils/auth');
 Page({
   data: {
     statusBarHeight: 20,
+    favRight: 8,
+    favTop: 20,
     id: '',
     planId: '',
     exercise: null,
     heroSrc: '',
+    heroGif: '',
     heroError: false,
     related: [],
     loading: true,
@@ -20,7 +23,18 @@ Page({
   onLoad(query) {
     const id = query.id || '';
     const planId = query.planId || '';
-    this.setData({ statusBarHeight: app.globalData.statusBarHeight || 20, id, planId });
+    // 收藏按钮需避让微信右上角胶囊按钮(···◯)：用胶囊实际位置算出安全右/上边距
+    let favRight = 8;
+    let favTop = (app.globalData.statusBarHeight || 20) + 6;
+    try {
+      const menu = wx.getMenuButtonBoundingClientRect();
+      const win = (wx.getWindowInfo && wx.getWindowInfo()) || wx.getSystemInfoSync();
+      if (menu && win) {
+        favRight = Math.max(8, win.windowWidth - menu.left + 8);
+        favTop = menu.top + Math.max(0, (menu.height - 36) / 2);
+      }
+    } catch (e) {}
+    this.setData({ statusBarHeight: app.globalData.statusBarHeight || 20, favRight, favTop, id, planId });
     // 防御：id 缺失直接显示空态，避免请求 /api/exercises/ 导致错乱或 404
     if (!id) {
       this.setData({ loading: false });
@@ -37,9 +51,10 @@ Page({
   load() {
     this.setData({ loading: true });
     svc.getExercise(this.data.id).then((ex) => {
-      // 详情大图优先用超分 JPG(720px 清晰)；失败再降级到 GIF / 占位
+      // 海报用超分 JPG(720px 清晰)；动图用原始 GIF，由 gif-player 组件逐帧播放
       const heroSrc = ex && (ex.image || ex.gifUrl) ? (ex.image || ex.gifUrl) : '';
-      this.setData({ exercise: ex, heroSrc, heroError: false, loading: false });
+      const heroGif = ex && ex.gifUrl ? ex.gifUrl : '';
+      this.setData({ exercise: ex, heroSrc, heroGif, heroError: false, loading: false });
       if (ex && ex.target) {
         svc.listExercises({ target: ex.target, pageSize: 6 }).then((res) => {
           const related = ((res && res.items) || [])

miniprogram/pages/detail/detail.json

@@ -2,6 +2,7 @@
   "navigationStyle": "custom",
   "usingComponents": {
     "navbar": "/components/navbar/index",
-    "exercise-card": "/components/exercise-card/index"
+    "exercise-card": "/components/exercise-card/index",
+    "gif-player": "/components/gif-player/gif-player"
   }
 }

miniprogram/pages/detail/detail.wxml

@@ -1,7 +1,7 @@
 <view class="page" wx:if="{{exercise}}">
   <navbar title="{{exercise.displayName || exercise.name}}" show-back />
 
-  <view class="favbtn" style="top: {{statusBarHeight + 12}}px;" bindtap="onToggleFav">
+  <view class="favbtn" style="top: {{favTop}}px; right: {{favRight}}px;" bindtap="onToggleFav">
     <text>{{favorited ? '♥' : '♡'}}</text>
   </view>
 
@@ -14,6 +14,8 @@
       lazy-load="true"
       binderror="onHeroError" />
     <view wx:else class="hero__ph">🏋️</view>
+    <!-- 上层叠一个动图播放器：Canvas 逐帧播放 GIF（微信 image 不播 GIF） -->
+    <gif-player wx:if="{{heroGif}}" class="hero__gif" src="{{heroGif}}" />
   </view>
 
   <view class="body section">

miniprogram/pages/detail/detail.wxss

@@ -1,7 +1,8 @@
 .page { min-height: 100vh; background: var(--bg-grad); padding-bottom: 180rpx; }
-.hero { width: 100%; height: 520rpx; background: var(--surface-2); }
+.hero { width: 100%; height: 520rpx; background: var(--surface-2); position: relative; }
 .hero__img { width: 100%; height: 100%; display: block; }
 .hero__ph { width: 100%; height: 100%; display: flex; align-items: center; justify-content: center; font-size: 120rpx; }
+.hero__gif { position: absolute; left: 0; top: 0; width: 100%; height: 100%; }
 
 .name { font-size: 48rpx; font-weight: 700; color: var(--text); letter-spacing: 1rpx; }
 

miniprogram/utils/vendor/omggif.js

@@ -0,0 +1,807 @@
+// (c) Dean McNamee <dean@gmail.com>, 2013.
+//
+// https://github.com/deanm/omggif
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to
+// deal in the Software without restriction, including without limitation the
+// rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+// sell copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+// IN THE SOFTWARE.
+//
+// omggif is a JavaScript implementation of a GIF 89a encoder and decoder,
+// including animation and compression.  It does not rely on any specific
+// underlying system, so should run in the browser, Node, or Plask.
+
+"use strict";
+
+function GifWriter(buf, width, height, gopts) {
+  var p = 0;
+
+  var gopts = gopts === undefined ? { } : gopts;
+  var loop_count = gopts.loop === undefined ? null : gopts.loop;
+  var global_palette = gopts.palette === undefined ? null : gopts.palette;
+
+  if (width <= 0 || height <= 0 || width > 65535 || height > 65535)
+    throw new Error("Width/Height invalid.");
+
+  function check_palette_and_num_colors(palette) {
+    var num_colors = palette.length;
+    if (num_colors < 2 || num_colors > 256 ||  num_colors & (num_colors-1)) {
+      throw new Error(
+          "Invalid code/color length, must be power of 2 and 2 .. 256.");
+    }
+    return num_colors;
+  }
+
+  // - Header.
+  buf[p++] = 0x47; buf[p++] = 0x49; buf[p++] = 0x46;  // GIF
+  buf[p++] = 0x38; buf[p++] = 0x39; buf[p++] = 0x61;  // 89a
+
+  // Handling of Global Color Table (palette) and background index.
+  var gp_num_colors_pow2 = 0;
+  var background = 0;
+  if (global_palette !== null) {
+    var gp_num_colors = check_palette_and_num_colors(global_palette);
+    while (gp_num_colors >>= 1) ++gp_num_colors_pow2;
+    gp_num_colors = 1 << gp_num_colors_pow2;
+    --gp_num_colors_pow2;
+    if (gopts.background !== undefined) {
+      background = gopts.background;
+      if (background >= gp_num_colors)
+        throw new Error("Background index out of range.");
+      // The GIF spec states that a background index of 0 should be ignored, so
+      // this is probably a mistake and you really want to set it to another
+      // slot in the palette.  But actually in the end most browsers, etc end
+      // up ignoring this almost completely (including for dispose background).
+      if (background === 0)
+        throw new Error("Background index explicitly passed as 0.");
+    }
+  }
+
+  // - Logical Screen Descriptor.
+  // NOTE(deanm): w/h apparently ignored by implementations, but set anyway.
+  buf[p++] = width & 0xff; buf[p++] = width >> 8 & 0xff;
+  buf[p++] = height & 0xff; buf[p++] = height >> 8 & 0xff;
+  // NOTE: Indicates 0-bpp original color resolution (unused?).
+  buf[p++] = (global_palette !== null ? 0x80 : 0) |  // Global Color Table Flag.
+             gp_num_colors_pow2;  // NOTE: No sort flag (unused?).
+  buf[p++] = background;  // Background Color Index.
+  buf[p++] = 0;  // Pixel aspect ratio (unused?).
+
+  // - Global Color Table
+  if (global_palette !== null) {
+    for (var i = 0, il = global_palette.length; i < il; ++i) {
+      var rgb = global_palette[i];
+      buf[p++] = rgb >> 16 & 0xff;
+      buf[p++] = rgb >> 8 & 0xff;
+      buf[p++] = rgb & 0xff;
+    }
+  }
+
+  if (loop_count !== null) {  // Netscape block for looping.
+    if (loop_count < 0 || loop_count > 65535)
+      throw new Error("Loop count invalid.")
+    // Extension code, label, and length.
+    buf[p++] = 0x21; buf[p++] = 0xff; buf[p++] = 0x0b;
+    // NETSCAPE2.0
+    buf[p++] = 0x4e; buf[p++] = 0x45; buf[p++] = 0x54; buf[p++] = 0x53;
+    buf[p++] = 0x43; buf[p++] = 0x41; buf[p++] = 0x50; buf[p++] = 0x45;
+    buf[p++] = 0x32; buf[p++] = 0x2e; buf[p++] = 0x30;
+    // Sub-block
+    buf[p++] = 0x03; buf[p++] = 0x01;
+    buf[p++] = loop_count & 0xff; buf[p++] = loop_count >> 8 & 0xff;
+    buf[p++] = 0x00;  // Terminator.
+  }
+
+
+  var ended = false;
+
+  this.addFrame = function(x, y, w, h, indexed_pixels, opts) {
+    if (ended === true) { --p; ended = false; }  // Un-end.
+
+    opts = opts === undefined ? { } : opts;
+
+    // TODO(deanm): Bounds check x, y.  Do they need to be within the virtual
+    // canvas width/height, I imagine?
+    if (x < 0 || y < 0 || x > 65535 || y > 65535)
+      throw new Error("x/y invalid.")
+
+    if (w <= 0 || h <= 0 || w > 65535 || h > 65535)
+      throw new Error("Width/Height invalid.")
+
+    if (indexed_pixels.length < w * h)
+      throw new Error("Not enough pixels for the frame size.");
+
+    var using_local_palette = true;
+    var palette = opts.palette;
+    if (palette === undefined || palette === null) {
+      using_local_palette = false;
+      palette = global_palette;
+    }
+
+    if (palette === undefined || palette === null)
+      throw new Error("Must supply either a local or global palette.");
+
+    var num_colors = check_palette_and_num_colors(palette);
+
+    // Compute the min_code_size (power of 2), destroying num_colors.
+    var min_code_size = 0;
+    while (num_colors >>= 1) ++min_code_size;
+    num_colors = 1 << min_code_size;  // Now we can easily get it back.
+
+    var delay = opts.delay === undefined ? 0 : opts.delay;
+
+    // From the spec:
+    //     0 -   No disposal specified. The decoder is
+    //           not required to take any action.
+    //     1 -   Do not dispose. The graphic is to be left
+    //           in place.
+    //     2 -   Restore to background color. The area used by the
+    //           graphic must be restored to the background color.
+    //     3 -   Restore to previous. The decoder is required to
+    //           restore the area overwritten by the graphic with
+    //           what was there prior to rendering the graphic.
+    //  4-7 -    To be defined.
+    // NOTE(deanm): Dispose background doesn't really work, apparently most
+    // browsers ignore the background palette index and clear to transparency.
+    var disposal = opts.disposal === undefined ? 0 : opts.disposal;
+    if (disposal < 0 || disposal > 3)  // 4-7 is reserved.
+      throw new Error("Disposal out of range.");
+
+    var use_transparency = false;
+    var transparent_index = 0;
+    if (opts.transparent !== undefined && opts.transparent !== null) {
+      use_transparency = true;
+      transparent_index = opts.transparent;
+      if (transparent_index < 0 || transparent_index >= num_colors)
+        throw new Error("Transparent color index.");
+    }
+
+    if (disposal !== 0 || use_transparency || delay !== 0) {
+      // - Graphics Control Extension
+      buf[p++] = 0x21; buf[p++] = 0xf9;  // Extension / Label.
+      buf[p++] = 4;  // Byte size.
+
+      buf[p++] = disposal << 2 | (use_transparency === true ? 1 : 0);
+      buf[p++] = delay & 0xff; buf[p++] = delay >> 8 & 0xff;
+      buf[p++] = transparent_index;  // Transparent color index.
+      buf[p++] = 0;  // Block Terminator.
+    }
+
+    // - Image Descriptor
+    buf[p++] = 0x2c;  // Image Seperator.
+    buf[p++] = x & 0xff; buf[p++] = x >> 8 & 0xff;  // Left.
+    buf[p++] = y & 0xff; buf[p++] = y >> 8 & 0xff;  // Top.
+    buf[p++] = w & 0xff; buf[p++] = w >> 8 & 0xff;
+    buf[p++] = h & 0xff; buf[p++] = h >> 8 & 0xff;
+    // NOTE: No sort flag (unused?).
+    // TODO(deanm): Support interlace.
+    buf[p++] = using_local_palette === true ? (0x80 | (min_code_size-1)) : 0;
+
+    // - Local Color Table
+    if (using_local_palette === true) {
+      for (var i = 0, il = palette.length; i < il; ++i) {
+        var rgb = palette[i];
+        buf[p++] = rgb >> 16 & 0xff;
+        buf[p++] = rgb >> 8 & 0xff;
+        buf[p++] = rgb & 0xff;
+      }
+    }
+
+    p = GifWriterOutputLZWCodeStream(
+            buf, p, min_code_size < 2 ? 2 : min_code_size, indexed_pixels);
+
+    return p;
+  };
+
+  this.end = function() {
+    if (ended === false) {
+      buf[p++] = 0x3b;  // Trailer.
+      ended = true;
+    }
+    return p;
+  };
+
+  this.getOutputBuffer = function() { return buf; };
+  this.setOutputBuffer = function(v) { buf = v; };
+  this.getOutputBufferPosition = function() { return p; };
+  this.setOutputBufferPosition = function(v) { p = v; };
+}
+
+// Main compression routine, palette indexes -> LZW code stream.
+// |index_stream| must have at least one entry.
+function GifWriterOutputLZWCodeStream(buf, p, min_code_size, index_stream) {
+  buf[p++] = min_code_size;
+  var cur_subblock = p++;  // Pointing at the length field.
+
+  var clear_code = 1 << min_code_size;
+  var code_mask = clear_code - 1;
+  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.
+  var cur_shift = 0;
+  // We have at most 12-bit codes, so we should have to hold a max of 19
+  // bits here (and then we would write out).
+  var cur = 0;
+
+  function emit_bytes_to_buffer(bit_block_size) {
+    while (cur_shift >= bit_block_size) {
+      buf[p++] = cur & 0xff;
+      cur >>= 8; cur_shift -= 8;
+      if (p === cur_subblock + 256) {  // Finished a subblock.
+        buf[cur_subblock] = 255;
+        cur_subblock = p++;
+      }
+    }
+  }
+
+  function emit_code(c) {
+    cur |= c << cur_shift;
+    cur_shift += cur_code_size;
+    emit_bytes_to_buffer(8);
+  }
+
+  // I am not an expert on the topic, and I don't want to write a thesis.
+  // However, it is good to outline here the basic algorithm and the few data
+  // structures and optimizations here that make this implementation fast.
+  // The basic idea behind LZW is to build a table of previously seen runs
+  // addressed by a short id (herein called output code).  All data is
+  // referenced by a code, which represents one or more values from the
+  // original input stream.  All input bytes can be referenced as the same
+  // value as an output code.  So if you didn't want any compression, you
+  // could more or less just output the original bytes as codes (there are
+  // some details to this, but it is the idea).  In order to achieve
+  // compression, values greater then the input range (codes can be up to
+  // 12-bit while input only 8-bit) represent a sequence of previously seen
+  // inputs.  The decompressor is able to build the same mapping while
+  // decoding, so there is always a shared common knowledge between the
+  // encoding and decoder, which is also important for "timing" aspects like
+  // how to handle variable bit width code encoding.
+  //
+  // One obvious but very important consequence of the table system is there
+  // is always a unique id (at most 12-bits) to map the runs.  'A' might be
+  // 4, then 'AA' might be 10, 'AAA' 11, 'AAAA' 12, etc.  This relationship
+  // can be used for an effecient lookup strategy for the code mapping.  We
+  // need to know if a run has been seen before, and be able to map that run
+  // to the output code.  Since we start with known unique ids (input bytes),
+  // and then from those build more unique ids (table entries), we can
+  // continue this chain (almost like a linked list) to always have small
+  // integer values that represent the current byte chains in the encoder.
+  // This means instead of tracking the input bytes (AAAABCD) to know our
+  // current state, we can track the table entry for AAAABC (it is guaranteed
+  // to exist by the nature of the algorithm) and the next character D.
+  // Therefor the tuple of (table_entry, byte) is guaranteed to also be
+  // unique.  This allows us to create a simple lookup key for mapping input
+  // sequences to codes (table indices) without having to store or search
+  // any of the code sequences.  So if 'AAAA' has a table entry of 12, the
+  // tuple of ('AAAA', K) for any input byte K will be unique, and can be our
+  // key.  This leads to a integer value at most 20-bits, which can always
+  // fit in an SMI value and be used as a fast sparse array / object key.
+
+  // Output code for the current contents of the index buffer.
+  var ib_code = index_stream[0] & code_mask;  // Load first input index.
+  var code_table = { };  // Key'd on our 20-bit "tuple".
+
+  emit_code(clear_code);  // Spec says first code should be a clear code.
+
+  // First index already loaded, process the rest of the stream.
+  for (var i = 1, il = index_stream.length; i < il; ++i) {
+    var k = index_stream[i] & code_mask;
+    var cur_key = ib_code << 8 | k;  // (prev, k) unique tuple.
+    var cur_code = code_table[cur_key];  // buffer + k.
+
+    // Check if we have to create a new code table entry.
+    if (cur_code === undefined) {  // We don't have buffer + k.
+      // Emit index buffer (without k).
+      // This is an inline version of emit_code, because this is the core
+      // writing routine of the compressor (and V8 cannot inline emit_code
+      // because it is a closure here in a different context).  Additionally
+      // we can call emit_byte_to_buffer less often, because we can have
+      // 30-bits (from our 31-bit signed SMI), and we know our codes will only
+      // be 12-bits, so can safely have 18-bits there without overflow.
+      // emit_code(ib_code);
+      cur |= ib_code << cur_shift;
+      cur_shift += cur_code_size;
+      while (cur_shift >= 8) {
+        buf[p++] = cur & 0xff;
+        cur >>= 8; cur_shift -= 8;
+        if (p === cur_subblock + 256) {  // Finished a subblock.
+          buf[cur_subblock] = 255;
+          cur_subblock = p++;
+        }
+      }
+
+      if (next_code === 4096) {  // Table full, need a clear.
+        emit_code(clear_code);
+        next_code = eoi_code + 1;
+        cur_code_size = min_code_size + 1;
+        code_table = { };
+      } else {  // Table not full, insert a new entry.
+        // Increase our variable bit code sizes if necessary.  This is a bit
+        // tricky as it is based on "timing" between the encoding and
+        // decoder.  From the encoders perspective this should happen after
+        // we've already emitted the index buffer and are about to create the
+        // first table entry that would overflow our current code bit size.
+        if (next_code >= (1 << cur_code_size)) ++cur_code_size;
+        code_table[cur_key] = next_code++;  // Insert into code table.
+      }
+
+      ib_code = k;  // Index buffer to single input k.
+    } else {
+      ib_code = cur_code;  // Index buffer to sequence in code table.
+    }
+  }
+
+  emit_code(ib_code);  // There will still be something in the index buffer.
+  emit_code(eoi_code);  // End Of Information.
+
+  // Flush / finalize the sub-blocks stream to the buffer.
+  emit_bytes_to_buffer(1);
+
+  // Finish the sub-blocks, writing out any unfinished lengths and
+  // terminating with a sub-block of length 0.  If we have already started
+  // but not yet used a sub-block it can just become the terminator.
+  if (cur_subblock + 1 === p) {  // Started but unused.
+    buf[cur_subblock] = 0;
+  } else {  // Started and used, write length and additional terminator block.
+    buf[cur_subblock] = p - cur_subblock - 1;
+    buf[p++] = 0;
+  }
+  return p;
+}
+
+function GifReader(buf) {
+  var p = 0;
+
+  // - Header (GIF87a or GIF89a).
+  if (buf[p++] !== 0x47 ||            buf[p++] !== 0x49 || buf[p++] !== 0x46 ||
+      buf[p++] !== 0x38 || (buf[p++]+1 & 0xfd) !== 0x38 || buf[p++] !== 0x61) {
+    throw new Error("Invalid GIF 87a/89a header.");
+  }
+
+  // - Logical Screen Descriptor.
+  var width = buf[p++] | buf[p++] << 8;
+  var height = buf[p++] | buf[p++] << 8;
+  var pf0 = buf[p++];  // <Packed Fields>.
+  var global_palette_flag = pf0 >> 7;
+  var num_global_colors_pow2 = pf0 & 0x7;
+  var num_global_colors = 1 << (num_global_colors_pow2 + 1);
+  var background = buf[p++];
+  buf[p++];  // Pixel aspect ratio (unused?).
+
+  var global_palette_offset = null;
+  var global_palette_size   = null;
+
+  if (global_palette_flag) {
+    global_palette_offset = p;
+    global_palette_size = num_global_colors;
+    p += num_global_colors * 3;  // Seek past palette.
+  }
+
+  var no_eof = true;
+
+  var frames = [ ];
+
+  var delay = 0;
+  var transparent_index = null;
+  var disposal = 0;  // 0 - No disposal specified.
+  var loop_count = null;
+
+  this.width = width;
+  this.height = height;
+
+  while (no_eof && p < buf.length) {
+    switch (buf[p++]) {
+      case 0x21:  // Graphics Control Extension Block
+        switch (buf[p++]) {
+          case 0xff:  // Application specific block
+            // Try if it's a Netscape block (with animation loop counter).
+            if (buf[p   ] !== 0x0b ||  // 21 FF already read, check block size.
+                // NETSCAPE2.0
+                buf[p+1 ] == 0x4e && buf[p+2 ] == 0x45 && buf[p+3 ] == 0x54 &&
+                buf[p+4 ] == 0x53 && buf[p+5 ] == 0x43 && buf[p+6 ] == 0x41 &&
+                buf[p+7 ] == 0x50 && buf[p+8 ] == 0x45 && buf[p+9 ] == 0x32 &&
+                buf[p+10] == 0x2e && buf[p+11] == 0x30 &&
+                // Sub-block
+                buf[p+12] == 0x03 && buf[p+13] == 0x01 && buf[p+16] == 0) {
+              p += 14;
+              loop_count = buf[p++] | buf[p++] << 8;
+              p++;  // Skip terminator.
+            } else {  // We don't know what it is, just try to get past it.
+              p += 12;
+              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
+                p += block_size;
+              }
+            }
+            break;
+
+          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) {}