[Bug]: GIF frames become skewed when using PillowWriter in matplotlib 3.11.1 #32186

from matplotlib import animation
from matplotlib import pyplot as plt

fig, ax = plt.subplots(figsize=(8.2, 7), dpi=100)
line, = ax.plot([], [])

def update(frame):
    line.set_data([0, 1], [0, frame])
    return line,

ani = animation.FuncAnimation(fig, update, frames=1, blit=False)

ani.save("test.gif", writer=animation.PillowWriter(fps=1), dpi=100)

plt.close(fig)

from io import BytesIO

import matplotlib

class DebugPillowWriter(animation.PillowWriter):
    def grab_frame(self, **savefig_kwargs):
        buffer = BytesIO()

        self.fig.savefig(
            buffer,
            format="rgba",
            dpi=self.dpi,
            **savefig_kwargs,
        )

        width, height = self.frame_size

        raw_size = buffer.getbuffer().nbytes
        expected_size = width * height * 4

        print("Matplotlib:", matplotlib.__version__)
        print("canvas size:", self.fig.canvas.get_width_height())
        print("frame size:", self.frame_size)
        print("raw size:", raw_size)
        print("expected size:", expected_size)

        return super().grab_frame(**savefig_kwargs)