66 lines
2.2 KiB
JavaScript
66 lines
2.2 KiB
JavaScript
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/*jslint browser: true, devel: true, bitwise: false, debug: true, eqeq: false, es5: true, evil: false, forin: false, newcap: false, nomen: true, plusplus: true, regexp: false, unparam: false, sloppy: true, stupid: false, sub: false, todo: true, vars: true, white: true */
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module.exports = {
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parseSections: function(stream, iterator) {
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var len, markerType;
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stream.setBigEndian(true);
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//stop reading the stream at the SOS (Start of Stream) marker,
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//because its length is not stored in the header so we can't
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//know where to jump to. The only marker after that is just EOI (End Of Image) anyway
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while(stream.remainingLength() > 0 && markerType !== 0xDA) {
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if(stream.nextUInt8() !== 0xFF) {
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throw new Error('Invalid JPEG section offset');
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}
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markerType = stream.nextUInt8();
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//don't read size from markers that have no datas
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if((markerType >= 0xD0 && markerType <= 0xD9) || markerType === 0xDA) {
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len = 0;
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} else {
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len = stream.nextUInt16() - 2;
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}
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iterator(markerType, stream.branch(0, len));
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stream.skip(len);
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}
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},
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//stream should be located after SOF section size and in big endian mode, like passed to parseSections iterator
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getSizeFromSOFSection: function(stream) {
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stream.skip(1);
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return {
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height: stream.nextUInt16(),
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width: stream.nextUInt16()
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};
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},
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getSectionName: function(markerType) {
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var name, index;
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switch(markerType) {
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case 0xD8: name = 'SOI'; break;
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case 0xC4: name = 'DHT'; break;
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case 0xDB: name = 'DQT'; break;
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case 0xDD: name = 'DRI'; break;
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case 0xDA: name = 'SOS'; break;
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case 0xFE: name = 'COM'; break;
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case 0xD9: name = 'EOI'; break;
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default:
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if(markerType >= 0xE0 && markerType <= 0xEF) {
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name = 'APP';
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index = markerType - 0xE0;
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}
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else if(markerType >= 0xC0 && markerType <= 0xCF && markerType !== 0xC4 && markerType !== 0xC8 && markerType !== 0xCC) {
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name = 'SOF';
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index = markerType - 0xC0;
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}
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else if(markerType >= 0xD0 && markerType <= 0xD7) {
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name = 'RST';
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index = markerType - 0xD0;
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}
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break;
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}
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var nameStruct = {
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name: name
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};
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if(typeof index === 'number') {
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nameStruct.index = index;
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}
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return nameStruct;
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}
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};
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