Hiren Kangad
e43f8eff07
Sharp-based service that produces thumb (256px), medium (1024px), and full (pass-through) tiers from an uploaded image buffer. Skips upscaling when the source is smaller than a tier's width.
67 lines
2.1 KiB
JavaScript
67 lines
2.1 KiB
JavaScript
const sharp = require('sharp');
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/**
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* LOD tier configuration.
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* Each tier defines the max width and WebP quality for that level of detail.
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* The 'full' tier is a pass-through (no resize, original format).
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*/
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const LOD_TIERS = {
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thumb: { maxWidth: 256, quality: 70 },
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medium: { maxWidth: 1024, quality: 80 },
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full: { maxWidth: null, quality: null },
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};
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/**
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* Generate 3-tier LOD images from an uploaded buffer.
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*
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* @param {Buffer} buffer - Original image buffer
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* @param {string} originalExt - Original file extension (e.g. '.png', '.jpg')
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* @returns {Promise<{
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* thumb: { buffer: Buffer, ext: string, width: number, height: number },
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* medium: { buffer: Buffer, ext: string, width: number, height: number },
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* full: { buffer: Buffer, ext: string, width: number, height: number }
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* }>}
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*/
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async function generateLOD(buffer, originalExt) {
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const metadata = await sharp(buffer).metadata();
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const origWidth = metadata.width;
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const origHeight = metadata.height;
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// Full tier — pass-through, no transformation
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const full = {
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buffer,
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ext: originalExt,
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width: origWidth,
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height: origHeight,
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};
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// Generate a resized WebP tier, or reuse original if image is already smaller
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async function makeTier(tierKey) {
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const { maxWidth, quality } = LOD_TIERS[tierKey];
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if (origWidth <= maxWidth) {
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// Image is smaller than tier width — convert to WebP but don't upscale
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const result = sharp(buffer).webp({ quality });
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const outBuf = await result.toBuffer();
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return { buffer: outBuf, ext: '.webp', width: origWidth, height: origHeight };
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}
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// Resize down (width-based, preserve aspect ratio)
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const result = sharp(buffer)
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.resize({ width: maxWidth, withoutEnlargement: true })
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.webp({ quality });
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const outBuf = await result.toBuffer();
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const outMeta = await sharp(outBuf).metadata();
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return { buffer: outBuf, ext: '.webp', width: outMeta.width, height: outMeta.height };
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}
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const [thumb, medium] = await Promise.all([
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makeTier('thumb'),
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makeTier('medium'),
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]);
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return { thumb, medium, full };
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}
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module.exports = { generateLOD, LOD_TIERS };
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