From 6f4874fa20d4fa156dd762d5dacefd8a2e656bf0 Mon Sep 17 00:00:00 2001 From: "caleb.mabry.15@cnu.edu" Date: Tue, 8 Mar 2022 23:07:09 -0500 Subject: Lots of changes --- webAO/utils/calculateGifLength.js | 27 +++++++++++++++++++++++++++ 1 file changed, 27 insertions(+) create mode 100644 webAO/utils/calculateGifLength.js (limited to 'webAO/utils/calculateGifLength.js') diff --git a/webAO/utils/calculateGifLength.js b/webAO/utils/calculateGifLength.js new file mode 100644 index 0000000..a57264d --- /dev/null +++ b/webAO/utils/calculateGifLength.js @@ -0,0 +1,27 @@ + /** + * 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 \ No newline at end of file -- cgit