Generalize pytest-mpl to support non-Matplotlib visual output

I am currently trying to use the Solara testing framework to try and do unit/regression testing of the rendering of Jupyter widgets, and I was wishing that I could just re-use all the pytest-mpl infrastructure to do figure hashes, galleries, etc. In a discussion with @Cadair we realised that it is possible, although a little ugly right now:

import ipywidgets as widgets
import matplotlib.pyplot as plt
import playwright.sync_api
import pytest
from IPython.display import display
from PIL import Image


@pytest.mark.mpl_image_compare(savefig_kwargs={"dpi": 100})
def test_scatter_solara(
    tmp_path,
    solara_test,
    page_session: playwright.sync_api.Page,
    assert_solara_snapshot,
):

    from glue_jupyter import jglue
    from IPython.display import display

    app = jglue()
    app.add_data(a={"x": [1, 2, 3], "y": [2, 3, 4]})
    scatter = app.scatter2d(show=False)
    display(scatter._layout)

    button_sel = page_session.locator("text=No selection")
    button_sel.wait_for()
    screenshot = page_session.screenshot()

    with open(tmp_path / "screenshot.png", "wb") as f:
        f.write(screenshot)

    image = Image.open(tmp_path / "screenshot.png")
    size_x, size_y = image.size

    fig = plt.figure(figsize=(size_x / 100, size_y / 100))
    ax = fig.add_axes([0, 0, 1, 1])
    ax.imshow(image)
    plt.axis("off")

    return fig

Basically one can in principle take any image output and show it in a Matplotlib figure. However this is a bit hacky, and what would be a lot nicer would be if we could generalize this plugin to allow for alternatives to what actually generates the images, with Matplotlib being just one (and given the plugin name the default) option.

To keep this simple, we could also simply allow the returned value from tests to be a PIL Image instance as this would already allow any arbitrary image generation in the tests.

Does anyone have any thoughts on this? Any reason to not at least allow PIL returns?

从现有的 pytest.mark.mpl_image_compare 入口点和 issue 中的示例测试开始，然后跟踪返回的 Matplotlib 图形如何转换为哈希和图库。定义受支持的不使用 Matplotlib 的返回路径，包括 PIL.Image，并验证图像比较、哈希和图库在没有 Matplotlib 包装器的情况下仍能正常工作。