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Code Issues Releases Wiki Activity

PngParser: Handle gAMA chunk

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This commit is contained in:
Jeff Schiller 2024-01-16 08:19:58 -08:00
parent b359f92251
commit 1d0abcaee8
3 changed files with 41 additions and 1 deletions
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32
image/parsers/png.js
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@ -14,12 +14,14 @@ import { ByteStream } from '../../io/bytestream.js';
// https://en.wikipedia.org/wiki/PNG#File_format
// https://www.w3.org/TR/2003/REC-PNG-20031110
// let DEBUG = true;
let DEBUG = false;
const SIG = new Uint8Array([0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A]);
/** @enum {string} */
export const PngParseEventType = {
IHDR: 'image_header',
gAMA: 'image_gamma',
PLTE: 'palette',
IDAT: 'image_data',
};
@ -59,6 +61,15 @@ export class PngImageHeaderEvent extends Event {
}
}
export class PngImageGammaEvent extends Event {
/** @param {number} */
constructor(gamma) {
super(PngParseEventType.gAMA);
/** @type {number} */
this.gamma = gamma;
}
}
/**
* @typedef PngColor
* @property {number} red
@ -132,6 +143,16 @@ export class PngParser extends EventTarget {
return this;
}
/**
* Type-safe way to bind a listener for a PngImageGammaEvent.
* @param {function(PngImageGammaEvent): void} listener
* @returns {PngParser} for chaining
*/
onGamma(listener) {
super.addEventListener(PngParseEventType.gAMA, listener);
return this;
}
/**
* Type-safe way to bind a listener for a PngPaletteEvent.
* @param {function(PngPaletteEvent): void} listener
@ -204,6 +225,12 @@ export class PngParser extends EventTarget {
this.dispatchEvent(new PngImageHeaderEvent(header));
break;
// https://www.w3.org/TR/2003/REC-PNG-20031110/#11gAMA
case 'gAMA':
if (length !== 4) throw `Bad length for gAMA: ${length}`;
this.dispatchEvent(new PngImageGammaEvent(chStream.readNumber(4)));
break;
// https://www.w3.org/TR/2003/REC-PNG-20031110/#11PLTE
case 'PLTE':
if (this.colorType === undefined) throw `PLTE before IHDR`;
@ -282,8 +309,11 @@ async function main() {
parser.onImageHeader(evt => {
// console.dir(evt.imageHeader);
});
parser.onGamma(evt => {
// console.dir(evt.imageGamma);
});
parser.onPalette(evt => {
console.dir(evt.palette);
// console.dir(evt.palette);
});
parser.onImageData(evt => {
// console.dir(evt);