lightposition for surface plots doesn't work

The parameter lightposition for surface plots expects an x, y, z vector. This vector is not explained in the documentation, does not make sense in any way, and playing with it only produces aggravation. It appears to be completely broken. This parameter should be defined in spherical coordinates and explained clearly in the documentation.

Not only does trying different values for x, y, z not make sense, I had a surface plot defined over the domains in x and y (my coordinates) of 0 to 6. I then realized that the domain should be -3 to 3; when I made this change, the lighting changed radically and I can't figure out how to get back the original lighting without reverting to the incorrect domains.

(1) lightposition needs to be fixed.

(2) lightposition needs to be in spherical coordinates.

(3) lightposition needs to be properly documented.

(4) lightposition needs to have at least an option which has a definition in "head" space so that the lighting doesn't change when merely the domain of the data is changed.

首先定位 surface-plot 的 lightposition 入口点及其文档；issue 未指定文件或测试。复现 x 和 y 域从 0–6 变为 -3–3 时的光照变化，然后定义所需的坐标行为。当该参数的行为一致、支持所请求的定位语义并且有清晰的文档说明时，即可视为完成。