catstodon/app/javascript/mastodon/utils/resize_image.js

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import EXIF from 'exif-js';
const MAX_IMAGE_PIXELS = 1638400; // 1280x1280px
const getImageUrl = inputFile => new Promise((resolve, reject) => {
if (window.URL && URL.createObjectURL) {
try {
resolve(URL.createObjectURL(inputFile));
} catch (error) {
reject(error);
}
return;
}
const reader = new FileReader();
reader.onerror = (...args) => reject(...args);
reader.onload = ({ target }) => resolve(target.result);
reader.readAsDataURL(inputFile);
});
const loadImage = inputFile => new Promise((resolve, reject) => {
getImageUrl(inputFile).then(url => {
const img = new Image();
img.onerror = (...args) => reject(...args);
img.onload = () => resolve(img);
img.src = url;
}).catch(reject);
});
const getOrientation = (img, type = 'image/png') => new Promise(resolve => {
if (type !== 'image/jpeg') {
resolve(1);
return;
}
EXIF.getData(img, () => {
const orientation = EXIF.getTag(img, 'Orientation');
resolve(orientation);
});
});
const processImage = (img, { width, height, orientation, type = 'image/png' }) => new Promise(resolve => {
const canvas = document.createElement('canvas');
if (4 < orientation && orientation < 9) {
canvas.width = height;
canvas.height = width;
} else {
canvas.width = width;
canvas.height = height;
}
const context = canvas.getContext('2d');
switch (orientation) {
case 2: context.transform(-1, 0, 0, 1, width, 0); break;
case 3: context.transform(-1, 0, 0, -1, width, height); break;
case 4: context.transform(1, 0, 0, -1, 0, height); break;
case 5: context.transform(0, 1, 1, 0, 0, 0); break;
case 6: context.transform(0, 1, -1, 0, height, 0); break;
case 7: context.transform(0, -1, -1, 0, height, width); break;
case 8: context.transform(0, -1, 1, 0, 0, width); break;
}
context.drawImage(img, 0, 0, width, height);
canvas.toBlob(resolve, type);
});
const resizeImage = (img, type = 'image/png') => new Promise((resolve, reject) => {
const { width, height } = img;
const newWidth = Math.round(Math.sqrt(MAX_IMAGE_PIXELS * (width / height)));
const newHeight = Math.round(Math.sqrt(MAX_IMAGE_PIXELS * (height / width)));
getOrientation(img, type)
.then(orientation => processImage(img, {
width: newWidth,
height: newHeight,
orientation,
type,
}))
.then(resolve)
.catch(reject);
});
export default inputFile => new Promise((resolve, reject) => {
if (!inputFile.type.match(/image.*/) || inputFile.type === 'image/gif') {
resolve(inputFile);
return;
}
loadImage(inputFile).then(img => {
if (img.width * img.height < MAX_IMAGE_PIXELS) {
resolve(inputFile);
return;
}
resizeImage(img, inputFile.type)
.then(resolve)
.catch(() => resolve(inputFile));
}).catch(reject);
});