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fix: smoother atlas zoom — proportional to deltaY instead of fixed 10% step
Trackpads send many small-delta wheel events, so the fixed 0.9/1.1 factor
made zooming feel jumpy. Now uses Math.pow(0.998, dy) for smooth scaling.
Mouse wheel (deltaMode=1) still feels snappy via line-to-pixel conversion.
Mobile pinch zoom was already proportional — unchanged.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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site/atlas.js
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site/atlas.js
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canvas.addEventListener('wheel', function(e) {
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e.preventDefault();
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var factor = e.deltaY > 0 ? 0.9 : 1.1;
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// scale zoom proportionally to deltaY — gentle for trackpad, snappy for mouse wheel
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// deltaMode 1 = lines (mouse wheel): multiply by 40 to approximate pixels
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var dy = e.deltaMode === 1 ? e.deltaY * 40 : e.deltaY;
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var factor = Math.pow(0.998, dy); // ~0.93 per 35px mouse tick, smooth for trackpad
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var newZoom = Math.max(view.minZoom, Math.min(view.maxZoom, view.zoom * factor));
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cacheTransform();
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var d = screenToData(e.clientX, e.clientY);