Flipping does not work as expected for ImageMobject

[UncraftedName]

Description of bug / unexpected behavior

Attempting to flip a ImageMobject across an axis does not seem to behave correctly. Flipping across the UP axis acts the same as a 180° rotation, while flipping across the RIGHT axis does nothing.

How to reproduce the issue

class Main(Scene):
    def construct(self):
        imgs = [ImageMobject("thinking.png").scale(0.1) for i in range(4)]
        self.add(Group(
            imgs[0],
            imgs[1].flip(),
            imgs[2].rotate(PI, UP),
            imgs[3].apply_matrix([[-1, 0], [0, 1]])
        ).arrange(RIGHT))

Additional media files

Images/GIFs

Additional comments

The only way I have figured out to flip images across a single axis so far is to edit the pixel array like so:

img.pixel_array = np.fliplr(img.pixel_array)  # for horizontal
img.pixel_array = np.flipud(img.pixel_array)  # for vertical

[behackl]

Just looked into this a bit. The proper way of fixing this would be to adapt the implementation in Camera.display_image_mobject -- basically, ImageMobjects are placed by specifying the coordinates of the upper left, upper right, and lower left corner (in ImageMobject.points). Manim is able to handle the case where the lower left corner is higher than the upper right corner (i.e., a flip along the horizontal axis), but curiously not when the upper right corner is left of the upper left corner (vertical flip).

[hennels]

I believe the problem mentioned by @behackl also occurs frequently in ThreeDScenes and leads to a rather comical effect. When an image is part of a ThreeDScene the flipping happens naturally during rotations causing the image to distort and flip wildly.

class ImageIn3D(ThreeDScene):
    def construct(self):
        image = ImageMobject(
            np.uint8(np.random.randint(256, size=(256, 256)))
        )
        image.rotate_about_origin(PI/4, axis=np.array([0., 1., 0.]), axes=[])
        image.shift(3*RIGHT)
        self.set_camera_orientation(phi=PI/3, theta=PI/4)
        self.add(Cube(fill_opacity=1.0))
        self.add(image)
        self.begin_ambient_camera_rotation(rate=PI/2)
        self.wait(4)
        self.stop_ambient_camera_rotation()

[hennels]

I believe this issue was fixed for the OpenGL renderer with #2534 as seen below. The distortion shown above and the flipping issue mentioned earlier seem to work now when OpenGL is used. The issues still exist with Cairo.