Feature: Support GIFs

Pronounce it however you like, we still synchronously support 'em.

Author: LaCuneta

package-lock.json

@@ -1,27 +1,33 @@
 {
   "name": "@netlogo/synchrodecoder",
-  "description": "A JavaScript library for synchronously decoding JPEGs and PNGs to binary data",
+  "description": "A JavaScript library for synchronously decoding GIFs, JPEGs, and PNGs to binary data",
   "version": "3.0.0",
   "author": "Center for Connected Learning (https://ccl.northwestern.edu/)",
   "contributors": [
     "Jason Bertsche <jason.bertsche@gmail.com> (https://www.github.com/TheBizzle)"
   ],
   "homepage": "https://ccl.northwestern.edu/netlogo",
-  "keywords": ["image", "png", "jpeg", "synchronous"],
+  "keywords": [
+    "image",
+    "png",
+    "jpeg",
+    "synchronous"
+  ],
   "license": "CC0-1.0",
   "repository": "https://github.com/NetLogo/SynchroDecoder",
   "dependencies": {
-    "upng-js": "2.1.0",
-    "jpeg-js": "0.4.4"
+    "jpeg-js": "0.4.4",
+    "omggif": "^1.0.10",
+    "upng-js": "2.1.0"
   },
   "devDependencies": {
-    "buffer":                       "6.0.3",
-    "grunt":                        "1.6.2",
-    "grunt-contrib-coffee":         "2.1.0",
-    "grunt-contrib-copy":           "1.0.0",
-    "grunt-rollup":                "12.0.0",
-    "grunt-terser":                 "2.0.0",
-    "@rollup/plugin-commonjs":     "29.0.2",
-    "@rollup/plugin-node-resolve": "16.0.3"
+    "@rollup/plugin-commonjs": "29.0.2",
+    "@rollup/plugin-node-resolve": "16.0.3",
+    "buffer": "6.0.3",
+    "grunt": "1.6.2",
+    "grunt-contrib-coffee": "2.1.0",
+    "grunt-contrib-copy": "1.0.0",
+    "grunt-rollup": "12.0.0",
+    "grunt-terser": "2.0.0"
   }
 }

package.json

@@ -1,7 +1,8 @@
 import { Buffer } from 'buffer/index.js'
 
-import PNG  from 'upng-js/UPNG.js'
-import JPEG from 'jpeg-js/index.js'
+import PNG              from 'upng-js/UPNG.js'
+import JPEG             from 'jpeg-js/index.js'
+import { GifReader }    from 'omggif'
 
 dataURIToBytes = (uri) ->
   raw = window.atob(uri.slice(uri.indexOf(",") + 1))
@@ -15,6 +16,7 @@ aIsPrefixOfB = (a, b) ->
 
 pngSignature = [0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A]
 jpgSignature = [0xFF, 0xD8, 0xFF]
+gifSignature = [0x47, 0x49, 0x46, 0x38]
 
 synchroDecoder =
   (b64) ->
@@ -44,6 +46,18 @@ synchroDecoder =
         else
           throw new Error("Converted JPEG bytes have length #{array.length}, but valid JPEG bytes would have length #{image.height * image.width * 4}.")
 
+      else if aIsPrefixOfB(gifSignature, bytes)
+
+        reader    = new GifReader(bytes)
+        pixelData = new Uint8Array(reader.width * reader.height * 4)
+        reader.decodeAndBlitFrameRGBA(0, pixelData)
+        array     = new Uint8ClampedArray(pixelData.buffer)
+
+        if array.length is (reader.height * reader.width * 4)
+          { array, height: reader.height, width: reader.width, didSucceed: true }
+        else
+          throw new Error("Converted GIF bytes have length #{array.length}, but valid GIF bytes would have length #{reader.height * reader.width * 4}.")
+
       else
         throw new Error("Undecodable file type")