Lots of changes

1 files changed, 27 insertions, 0 deletions

diff --git a/webAO/utils/calculateGifLength.js b/webAO/utils/calculateGifLength.js
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index 0000000..a57264d
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+++ b/webAO/utils/calculateGifLength.js
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+  /**
+	 * Adds up the frame delays to find out how long a GIF is
+	 * I totally didn't steal this
+	 * @param {data} gifFile the GIF data
+	 */
+const calculateGifLength = (gifFile) => {
+    const d = new Uint8Array(gifFile);
+    // Thanks to http://justinsomnia.org/2006/10/gif-animation-duration-calculation/
+    // And http://www.w3.org/Graphics/GIF/spec-gif89a.txt
+    let duration = 0;
+    for (let i = 0; i < d.length; i++) {
+      // Find a Graphic Control Extension hex(21F904__ ____ __00)
+      if (d[i] === 0x21
+				&& d[i + 1] === 0xF9
+				&& d[i + 2] === 0x04
+				&& d[i + 7] === 0x00) {
+        // Swap 5th and 6th bytes to get the delay per frame
+        const delay = (d[i + 5] << 8) | (d[i + 4] & 0xFF);
+
+        // Should be aware browsers have a minimum frame delay
+        // e.g. 6ms for IE, 2ms modern browsers (50fps)
+        duration += delay < 2 ? 10 : delay;
+      }
+    }
+    return duration * 10;
+  }
+  export default calculateGifLength
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