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pythonmanim

manim copy and property propagation (rectangle grid_xstep)

I'm starting with manim (Manim Community v0.17.1) and I got behaviors that I can't explain on some very basic example, any help appreciated.

class SquareScene(Scene):
    def construct(self):
        kwargs = {"fill_opacity": 1, "stroke_color": WHITE}

        square1 = Square(5, color=RED, grid_xstep=1, grid_ystep=1, **kwargs)
        square2 = square1.copy().set(color=BLUE, **kwargs).shift(UP + RIGHT)

        self.add(square2, square1)
  • square1 is displayed without a grid, I don't know why
  • square2 does have a grid

EDIT: I managed to solve the problem by setting fill_color=RED instead of color=RED. As I noticed the grid was there but also RED hence not visible.

Still it doesn't explain why the BLUE square grid color was WHITE then..

rectangles

Solution

  • Looking at how Square processes grid_xstep and grid_ystep (see https://github.com/ManimCommunity/manim/blob/9efe81daa3e88e25244affd3700e2d2a8b527635/manim/mobject/geometry/polygram.py#L552-L581), I would actually consider this behavior a bug: the method only passes the color keyword argument to the constructed Line objects.

    The construction of the lines also happens right at the end of the constructor; the color / fill color / stroke color of the parent mobject, the Square, have already been set at that point. Setting them (again) after the mobject has been constructed then also properly handles the color of the grid lines.

    Feel free to open a bug report over at https://github.com/ManimCommunity/manim!