Also look at the LuaMetaFun manual chapter 8. In fact the whole manual is worth a read. I'm sure you find much of use in it.
Best Wishes
Keith 

On Thu, 5 Oct 2023, 20:52 Henning Hraban Ramm, <texml@fiee.net> wrote:
Am 05.10.23 um 21:50 schrieb Fabrice Couvreur:
> Hi,
> I would like to obtain, if possible, a gray gradient like in the image.
> My code uses Metapost but maybe this is possible with Metafun.

Have a look into the Metafun manual, chapter 8.1 “shading”.

Hraban

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