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Fix linearLikeSteps with exponential scaling for perceptually linear zoom progression #256

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Fix linearLikeSteps with exponential scaling for perceptually linear zoom progression #256

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619b4ef
Initial plan
Copilot Dec 17, 2025
f08b4e6
Fix linearLikeSteps algorithm with proper logarithmic scaling
Copilot Dec 17, 2025
98a6f4e
Adjust exponential base to 4.0 for better zoom distribution
Copilot Dec 17, 2025
8b17708
Address code review: improve documentation and comments
Copilot Dec 17, 2025
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14 changes: 11 additions & 3 deletions src/main/kotlin/dev/isxander/zoomify/zoom/ZoomHelper.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -53,9 +53,17 @@ class ZoomHelper(
scrollTiers.toDouble() / Zoomify.maxScrollTiers
else 0.0
if (linearLikeSteps()) {
val curvature = 0.3
val exp = 1 / (1 - curvature)
targetZoom = 2 * (targetZoom.pow(exp) / (targetZoom.pow(exp) + (2 - targetZoom).pow(exp)))
// Use exponential scaling to make each zoom step feel equally significant
// Maps linear input (0 to 1) to exponential output
// This ensures each scroll step represents a constant multiplicative change in zoom
if (targetZoom > 0.0) {
// Base of 4.0 chosen empirically:
// - Provides good balance between early and late zoom steps
// - At 50% scroll: ~33% of max zoom (reasonable middle ground)
// - Creates perceptually linear zoom progression
val base = 4.0
targetZoom = (base.pow(targetZoom) - 1.0) / (base - 1.0)
}
}

prevScrollInterpolation = scrollInterpolation
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