2024-02-19 10:23:06 +08:00
|
|
|
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};
|
|
|
|
}
|
2024-11-02 13:34:09 +08:00
|
|
|
|
|
|
|
export function isImageFile(name) {
|
|
|
|
return /\.(jpe?g|png|gif|webp|svg|heic)$/i.test(name);
|
|
|
|
}
|