46 lines
1.7 KiB
Markdown
46 lines
1.7 KiB
Markdown
---
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title: Extract Thumbnail Image from Affinity Photo and Affinity Design
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---
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Nextcloud doesn't have a support for thumbnail generation from Affinity Photo and Affinity Design. So I had to do it myself.
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# Digging Binary
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Glancing at `.afphoto` and `.afdesign` in Finder, I noticed that it has a QuickLook support and an ability to show the thumbnail image. So these files should have thumbnail image somewhere inside its binary.
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I wrote a simple script to seek for thumbnail image from a binary and save it as `.png` file.
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```js af.js
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const fs = require("fs");
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// png spec: https://www.w3.org/TR/PNG/
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const PNG_SIG = Buffer.from([137, 80, 78, 71, 13, 10, 26, 10]);
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const IEND_SIG = Buffer.from([73, 69, 78, 68]);
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function extractThumbnail(buf) {
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const start = buf.indexOf(PNG_SIG);
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const end = buf.indexOf(IEND_SIG, start) + IEND_SIG.length * 2; // IEND + CRC
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return buf.subarray(start, end);
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}
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function generateThumbnail(input, output) {
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const buf = fs.readFileSync(input);
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const thumbBuf = extractThumbnail(buf);
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fs.writeFileSync(output, thumbBuf);
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}
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generateThumbnail(process.argv[2], process.argv[3] || "output.png");
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```
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That's right. This script just scrapes a binary file and extracts the portion of which starts with `PNG` signature and ends with `IEND`.
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Now I can generate a thumbnail image from arbitrary `.afphoto` and `.afdesign` file. Let's move on delving into Nextcloud source code.
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# Tweaking Nextcloud
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I have a little experience in tweaking Nextcloud source code before, where I implemented thumbnail generator for PDFs, so it should be easier this time, hopefully.
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Anyway, long story short, I got Nextcloud generates thumbnail images for Affinity files by implementing PreviewGenerator class.
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