Downscale pasted PNG images based on metadata (#29123)

Some images like MacOS screenshots contain
[pHYs](http://www.libpng.org/pub/png/book/chapter11.html#png.ch11.div.8)
data which we can use to downscale uploaded images so they render in the
same dppx ratio in which they were taken.

Before:

<img width="584" alt="image"
src="https://github.com/go-gitea/gitea/assets/115237/50979e3a-5d5a-40dc-a0a4-36eb6e28f14a">

After:

<img width="329" alt="image"
src="https://github.com/go-gitea/gitea/assets/115237/0690902a-f2fe-4c6b-97b3-6fdd67c21bad">

(cherry picked from commit 5e72526da4e915791f03af056890e16821bde052)
This commit is contained in:
silverwind 2024-02-19 03:23:06 +01:00 committed by Earl Warren
parent bb911b2d5f
commit b3f2447bc4
No known key found for this signature in database
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3 changed files with 93 additions and 3 deletions

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@ -1,5 +1,7 @@
import $ from 'jquery';
import {htmlEscape} from 'escape-goat';
import {POST} from '../../modules/fetch.js';
import {imageInfo} from '../../utils/image.js';
async function uploadFile(file, uploadUrl) {
const formData = new FormData();
@ -109,10 +111,22 @@ const uploadClipboardImage = async (editor, dropzone, e) => {
const placeholder = `![${name}](uploading ...)`;
editor.insertPlaceholder(placeholder);
const data = await uploadFile(img, uploadUrl);
editor.replacePlaceholder(placeholder, `![${name}](/attachments/${data.uuid})`);
const $input = $(`<input name="files" type="hidden">`).attr('id', data.uuid).val(data.uuid);
const {uuid} = await uploadFile(img, uploadUrl);
const {width, dppx} = await imageInfo(img);
const url = `/attachments/${uuid}`;
let text;
if (width > 0 && dppx > 1) {
// Scale down images from HiDPI monitors. This uses the <img> tag because it's the only
// method to change image size in Markdown that is supported by all implementations.
text = `<img width="${Math.round(width / dppx)}" alt="${htmlEscape(name)}" src="${htmlEscape(url)}">`;
} else {
text = `![${name}](${url})`;
}
editor.replacePlaceholder(placeholder, text);
const $input = $(`<input name="files" type="hidden">`).attr('id', uuid).val(uuid);
$files.append($input);
}
};

47
web_src/js/utils/image.js Normal file
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@ -0,0 +1,47 @@
export async function pngChunks(blob) {
const uint8arr = new Uint8Array(await blob.arrayBuffer());
const chunks = [];
if (uint8arr.length < 12) return chunks;
const view = new DataView(uint8arr.buffer);
if (view.getBigUint64(0) !== 9894494448401390090n) return chunks;
const decoder = new TextDecoder();
let index = 8;
while (index < uint8arr.length) {
const len = view.getUint32(index);
chunks.push({
name: decoder.decode(uint8arr.slice(index + 4, index + 8)),
data: uint8arr.slice(index + 8, index + 8 + len),
});
index += len + 12;
}
return chunks;
}
// decode a image and try to obtain width and dppx. If will never throw but instead
// return default values.
export async function imageInfo(blob) {
let width = 0; // 0 means no width could be determined
let dppx = 1; // 1 dot per pixel for non-HiDPI screens
if (blob.type === 'image/png') { // only png is supported currently
try {
for (const {name, data} of await pngChunks(blob)) {
const view = new DataView(data.buffer);
if (name === 'IHDR' && data?.length) {
// extract width from mandatory IHDR chunk
width = view.getUint32(0);
} else if (name === 'pHYs' && data?.length) {
// extract dppx from optional pHYs chunk, assuming pixels are square
const unit = view.getUint8(8);
if (unit === 1) {
dppx = Math.round(view.getUint32(0) / 39.3701) / 72; // meter to inch to dppx
}
}
}
} catch {}
}
return {width, dppx};
}

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@ -0,0 +1,29 @@
import {pngChunks, imageInfo} from './image.js';
const pngNoPhys = 'data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAAAAAA6fptVAAAADUlEQVQIHQECAP3/AAAAAgABzePRKwAAAABJRU5ErkJggg==';
const pngPhys = 'data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAIAAAACCAIAAAD91JpzAAAACXBIWXMAABYlAAAWJQFJUiTwAAAAEElEQVQI12OQNZcAIgYIBQAL8gGxdzzM0A==';
const pngEmpty = 'data:image/png;base64,';
async function dataUriToBlob(datauri) {
return await (await globalThis.fetch(datauri)).blob();
}
test('pngChunks', async () => {
expect(await pngChunks(await dataUriToBlob(pngNoPhys))).toEqual([
{name: 'IHDR', data: new Uint8Array([0, 0, 0, 1, 0, 0, 0, 1, 8, 0, 0, 0, 0])},
{name: 'IDAT', data: new Uint8Array([8, 29, 1, 2, 0, 253, 255, 0, 0, 0, 2, 0, 1])},
{name: 'IEND', data: new Uint8Array([])},
]);
expect(await pngChunks(await dataUriToBlob(pngPhys))).toEqual([
{name: 'IHDR', data: new Uint8Array([0, 0, 0, 2, 0, 0, 0, 2, 8, 2, 0, 0, 0])},
{name: 'pHYs', data: new Uint8Array([0, 0, 22, 37, 0, 0, 22, 37, 1])},
{name: 'IDAT', data: new Uint8Array([8, 215, 99, 144, 53, 151, 0, 34, 6, 8, 5, 0, 11, 242, 1, 177])},
]);
expect(await pngChunks(await dataUriToBlob(pngEmpty))).toEqual([]);
});
test('imageInfo', async () => {
expect(await imageInfo(await dataUriToBlob(pngNoPhys))).toEqual({width: 1, dppx: 1});
expect(await imageInfo(await dataUriToBlob(pngPhys))).toEqual({width: 2, dppx: 2});
expect(await imageInfo(await dataUriToBlob(pngEmpty))).toEqual({width: 0, dppx: 1});
});