Moving point with a color-gradient trail

Keywords: animation · PointPath · trail · gradient

A point orbits in a circle while a PointPath with pop_colors=False draws its trailing path. The trail uses a fixed red-to-orange gradient so that the head is bright and the tail fades to dark red.

Run

uv run python py/examples/viz/animation/point_path_trail.py

Source

viz/animation/point_path_trail.py

Code

# SPDX-License-Identifier: Apache-2.0
# Copyright 2021 Christian Perwass

"""point_path_trail.py — Moving point with a color-gradient trail.

A point orbits in a circle while a ``PointPath`` with ``pop_colors=False``
draws its trailing path.  The trail uses a fixed red-to-orange gradient
so that the head is bright and the tail fades to dark red.

Run with:  uv run python py/examples/viz/animation/point_path_trail.py

Keywords: animation, PointPath, trail, gradient
"""

import math

from pytanga.geometry import Point
from pytanga.viz import (
    LabelStyle,
    PointPath,
    PointPathStyle,
    PointStyle,
    Visualizer,
    gradient_colors,
)

# ── Setup ──────────────────────────────────────────────────
viz = Visualizer(title="Tanga — PointPath Trail Demo")
viz.show()

TRAIL_LENGTH = 150

# Create a 150-color gradient: dark red at the tail → bright orange at the head
trail_gradient = gradient_colors("#440000", "#ffaa00", TRAIL_LENGTH)

# PointPath with anchored colors (pop_colors=False):
# points shift through a fixed color gradient — the tail is always dark,
# the head is always bright
trail = PointPath(
    max_points=TRAIL_LENGTH, pop_colors=False, default_colors=trail_gradient
)

# Pre-fill the trail with the origin so it draws immediately
# (otherwise it needs 2+ points to render)
for _ in range(TRAIL_LENGTH):
    trail.add((0, 0, 0))

trail_ref = viz.new(trail, style=PointPathStyle(line_thickness=2))

# The moving object itself
point_ref = viz.new(
    Point(3, 0, 0),
    color="#ffaa00",
    label="object",
    style=PointStyle(size=0.12),
    label_style=LabelStyle(align=(0, 0)),
)

viz.flush()

# ── Animation loop ─────────────────────────────────────────
print("Animating circular orbit with gradient trail until Ctrl+C...")
angle = 0.0
for _ in viz.animate(fps=60):
    angle += 0.04  # radians per frame
    x = 3 * math.cos(angle)
    y = 3 * math.sin(angle)
    z = math.sin(angle * 0.5) * 0.5  # slight vertical oscillation

    # Move the object
    point_ref.entity = Point(x, y, z)

    # Extend the trail
    trail.add((x, y, z))
    trail_ref.entity = trail

    viz.flush()

print("Animation stopped.")