How to draw STRAIGHT lines in manim?

Question

I want to create a video with manim, which includes some straight lines.

Manim's class Line is actually line segments. Changing the buff attribute to an negative value doesn't work. I tried to calculate the intersect of the line with the screen border, but it's too complicated. Then I expand the line like this:

def expand_line(line: Line, ratio=100) -> None:
    ends = line.get_start_and_end()
    delta = ends[1] - ends[0]
    line.put_start_and_end_on(ends[0] - ratio * delta, ends[1] + ratio * delta)

It works well; but the animations like Create goes too fast.

Are there any classes or other better ways to draw straight lines?

Answer 1

I tried to calculate the intersect of the line with the screen border, but it's too complicated.

You had the right idea here. Here's my solution:

class Test(Scene):
    def extend_line(self, line: Sequence[np.ndarray], **kwargs):
        sr_points = ScreenRectangle(height=config.frame_height).get_vertices()
        inters = []
        for i in adjacent_pairs(sr_points):
            inters += [line_intersection(i, line)]
        inters.sort(key=np.linalg.norm)  # we want the nearest intersections
        return Line(*inters[:2], **kwargs)

    def construct(self):
        a = self.extend_line([LEFT * 2, UP])
        self.wait()
        self.play(Create(a))