Volume on non-uniform grid does not appear

Plotting a 3D volume with a non-uniform grid yields a blank canvas with only the axes and the side bar.

Non-uniform means that the x, y, and z parameters are not simply obtained from a call to mgrid. For my application, they correspond to an affine transformation of such a regular grid, exactly like in https://community.plotly.com/t/3d-volume-plotting-with-non-orthogonal-grid/51662. There is also a StackOverflow answer pointing to this problem: https://stackoverflow.com/questions/66141821/plotting-a-3d-volume-plot-in-r-using-discrete-3d-points#answers.

This is either a bug or simply a documentation mistake, since the reference explicitly states that the coordinates should come from a "uniform or non-uniform 3-D grid" (see https://plotly.com/javascript/reference/volume/#volume).

Reproducer: https://codepen.io/Liozou/pen/OJaQMzK. On the left, the expected behavior, working on a uniform grid. On the right, the issue, on an affine-transformed grid. Black dots are used to visualize the grid itself.

从链接的 CodePen 复现示例开始，在 volume trace 中比较 uniform-grid 和 affine-transformed 两种情况。阅读 volume 参考文档，尤其是其中的坐标要求，然后跟踪 volume rendering 的入口点，以确定 non-uniform grid 产生空白 canvas 的原因。当 affine-transformed volume 能够渲染，同时现有的 uniform-grid 行为保持不变时，即表示完成。