Line

Qualified name: algan.mobs.shapes\_2d.Line

class Line(start=tensor([-1., -0., -0.]), end=tensor([1., 0., 0.]), buff=0, path_arc=0, *args, **kwargs)

Bases: BezierCircuitCubic

A straight or circular-arc line segment, drawn as a cubic bezier circuit.

A Line has no interior, so its stroke stays centred on the path rather than being drawn inside an outline the way a filled shape’s border is.

A straight line’s control points are collinear, which has two consequences worth relying on. Its local frame’s first basis row points from the line’s centre toward get_start() – that is a guarantee, not an accident of how the frame is derived. And its second row is synthesized perpendicular to the path rather than measured from it, so the texture grid defaults to grid_width samples along the line and a single row across it. Color along the line with set_color_by_function(), which parametrizes it by t running from the start to the end.

Parameters:

• start – The endpoints, shape (*, 3) in world units, or a Mob to attach to. Given a Mob, the line stops at its boundary in the direction of travel rather than at its center, so it never disappears underneath it. Default to LEFT and RIGHT.

• end – The endpoints, shape (*, 3) in world units, or a Mob to attach to. Given a Mob, the line stops at its boundary in the direction of travel rather than at its center, so it never disappears underneath it. Default to LEFT and RIGHT.

• buff – Gap left at each end, in world units, so a line between two labelled points does not touch them. Defaults to 0 (no gap).

• path_arc – Angle of the circular arc bulging the line away from straight, in radians – a Manim-parity argument, which is why it contradicts Algan’s usual degrees. Positive and negative values bulge opposite ways. Defaults to 0 (a straight segment).

• *args – Passed to BezierCircuitCubic – notably color, stroke_width and grid_width.

• **kwargs – Passed to BezierCircuitCubic – notably color, stroke_width and grid_width.

Examples

A straight line and an arc between the same two points:

Example: Example1Line

from algan import *

Line(LEFT, RIGHT, color=BLUE).spawn()
Line(LEFT, RIGHT, path_arc=1.0, color=YELLOW).spawn()

Scene.save_video()

Methods

get_end
get_length
get_start
get_unit_vector
get_vector
put_start_and_end_on
set_color_by_function	Color the line by a function of t, its progress from start to end.

Attributes

animation_manager	This mob's scene-owned animation manager.
basis	The Mob's orientation and scale, as a flattened 3x3 matrix of shape (*, 9).
casts_shadows	Whether this Mob's geometry blocks light on its way from a light source to another surface -- whether it casts a shadow.
children	The Mobs attached below this one, in attachment order.
closed_shell	Whether this Mob's triangles form a CLOSED shell -- every camera ray that enters the geometry crosses a second time on its way out.
draws_descendants	Whether get_render_primitives returns geometry belonging to this Mob's DESCENDANTS as well as its own.
forward	Get the direction the Mob is facing.
lifespan	This mob's [spawn, despawn) interval on its Scene timeline (a Lifespan).
location	The Mob's position in world space, shape (*, 3).
normalized_basis	The Mob's orientation with scale divided out, shape (*, 9).
parents	The Mobs this one is attached to, in attachment order.
receives_shadows	Whether this Mob's surfaces are darkened by shadows cast onto them.
right	Get the Mob's own rightward direction.
scale_coefficient	The Mob's scale along its own right, up and forward axes, shape (*, 3).
stroke_color	The color of the circuit's border stroke.
two_sided	Whether this Mob's geometry should be lit from whichever side the ray arrives on.
up	Get the Mob's own upward direction.
x	The Mob's x coordinate in world units, shape (*, 1).
xy	The Mob's x and y coordinates in world units, shape (*, 2).
y	The Mob's y coordinate in world units, shape (*, 1).
z	The Mob's z coordinate in world units, shape (*, 1).
z_index	Which of two exactly coplanar circuits draws in front (higher wins).

set_color_by_function(function)

Color the line by a function of t, its progress from start to end.

The same as BezierCircuitCubic.set_color_by_function, except that a line is one-dimensional: instead of (u, v) coordinates over a 2-D frame, the function is handed a single t running from 0 at get_start() to 1 at get_end(). A gradient along a line, or a value plotted onto one, is written directly in those terms.

A line is unfilled, so this colors its stroke. The resolution is the line’s texture grid, which is one flat color unless you asked for more: build it with grid_width (Line(LEFT, RIGHT, grid_width=64)). The height defaults to a single row across the line, so grid_width alone is the number of color samples along it.

Animation

Recorded as an animation over the current context’s runtime (1 second by default), so the colors cross-fade smoothly. Wrap the call in Off() to apply it instantly.

Parameters:

function – Callable taking a t tensor of shape [..., 1], in [0, 1], and returning colors of shape [..., 3] (RGB), [..., 4] (RGBA) or [..., 5] (RGB, glow, alpha – Algan’s internal channel order). Channels are in [0, 1]; a missing alpha defaults to 1 and a missing glow to 0. Must be vectorized – it is called once on the whole grid, not per texel.

Returns:

This line, so calls can be chained.

Return type:

Line

Raises:

ValueError – If the line has a single-texel texture grid, or if function returns the wrong number of colors.

Examples

Example: Example1LineSetColorByFunction

from algan import *
import torch

line = Line(LEFT * 3, RIGHT * 3, stroke_width=20, grid_width=64)
line.set_color_by_function(
    lambda t: torch.cat((t, torch.zeros_like(t), 1 - t), -1)
)
line.spawn()

Scene.save_video()