Feat/line graph smoothing#1312
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Adds a litmus example demonstrating how smooth line rendering overshoots the actual data range on steep slopes (steps, spikes, zeros, uneven x spacing), making values appear incorrect. Dashed MarkerLines mark the data min/max so any curve crossing them is an overshoot artifact.
Adds monotone cubic interpolation (Fritsch-Carlson, same algorithm
as d3 curveMonotoneX) as an alternative smoothing mode. Unlike the
default bezier smoothing, the monotone curve never overshoots the
vertical range of the data, so flat segments stay flat and steep
transitions cannot produce phantom values.
smooth={true} keeps the existing bezier behavior and smoothingRatio
continues to apply to it; smooth=monotone ignores the ratio.
Works for both line and area rendering.
The smoothing-overshoot litmus now renders two identical charts
side by side with a smoothing mode selector on each for direct
comparison.
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LineGraph: monotone smoothing mode (
smooth="monotone")Bezier smoothing (
smooth={true}) overshoots the data range on steep slopes —curves dip below zero on non-negative series or bulge past the actual maximum,
making values appear that don't exist in the data.
This PR adds
smooth="monotone": monotone cubic interpolation (Fritsch–Carlson,same algorithm as d3's
curveMonotoneX). Tangents are clamped at local extrema,so the curve is guaranteed to stay within the vertical bounds of the data. Works
for both line and area rendering.
smooth={true}is unchanged;smoothingRatioapplies to bezier only.features/charts/line-graph/SmoothingOvershoot.js) compares bothmodes side by side on datasets engineered to trigger overshoot.
[dataMin, dataMax]on alllitmus datasets and edge cases (two-point spans, duplicate x).