'use strict';
// based on developers.google.com/speed/webp/docs/riff_container
function isWebP (buffer) {
var riffHeader = 'RIFF' === buffer.toString('ascii', 0, 4); var webpHeader = 'WEBP' === buffer.toString('ascii', 8, 12); var vp8Header = 'VP8' === buffer.toString('ascii', 12, 15); return (riffHeader && webpHeader && vp8Header);
}
function calculate (buffer) {
var chunkHeader = buffer.toString('ascii', 12, 16); buffer = buffer.slice(20, 30); // Lossless webp stream signature if (chunkHeader === 'VP8 ' && buffer[0] !== 0x2f) { return calculateLossy(buffer); } // Lossy webp stream signature var signature = buffer.toString('hex', 3, 6); if (chunkHeader === 'VP8L' && signature !== '9d012a') { return calculateLossless(buffer); } return false;
}
function calculateLossless (buffer) {
return { 'width': 1 + (((buffer[2] & 0x3F) << 8) | buffer[1]), 'height': 1 + (((buffer[4] & 0xF) << 10) | (buffer[3] << 2) | ((buffer[2] & 0xC0) >> 6)) };
}
function calculateLossy (buffer) {
// `& 0x3fff` returns the last 14 bits // TO-DO: include webp scaling in the calculations return { 'width': buffer.readInt16LE(6) & 0x3fff, 'height': buffer.readInt16LE(8) & 0x3fff };
}
module.exports = {
'detect': isWebP, 'calculate': calculate
};