1D Point Widget

A free-moving (x, y) control point on a 1-D panel, with an optional crosshair. Unlike the vertical / horizontal line widgets it moves in both directions, so it is handy as a draggable data cursor or a control handle for an interactive fit. Add it with add_point_widget().

import numpy as np
import anyplotlib as apl

x = np.linspace(0, 4 * np.pi, 400)
y = np.sin(x) * np.exp(-x / 12)

fig, ax = apl.subplots(1, 1, figsize=(560, 340))
plot = ax.plot(y, axes=[x], color="#4fc3f7")

point = plot.add_point_widget(x=3.0, y=0.5, color="#ff1744",
                              show_crosshair=True)

fig

Snap the point onto the curve

A pointer_move handler fires while the point is dragged. Here we read point.x, look up the nearest sample, and push the point back onto the curve with set() — a one-line “snap to data” cursor.

@point.add_event_handler("pointer_move")
def _snap(event):
    i = int(np.clip(np.searchsorted(x, point.x), 0, len(x) - 1))
    point.set(y=float(y[i]))


fig.set_help("Drag the point — it snaps onto the curve as you move it.")

fig  # Interactive

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