# P3D Formula : opposite of screenX and screenY is ...?

**URL:** <https://discourse.processing.org/t/p3d-formula-opposite-of-screenx-and-screeny-is/10121>\
**Category:** Processing\
**Created:** [April 9, 2019, 10:17am UTC](https://discourse.processing.org/t/p3d-formula-opposite-of-screenx-and-screeny-is/10121 "2019-04-09T10:17:07Z")\
**Posts on this page:** 1\
**Showing post:** 3

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**Author:** ![Chrisir](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.processing.org/chrisir/32/45_2.png) [@Chrisir](https://discourse.processing.org/u/Chrisir)\
**Post date:** [April 12, 2019, 9:18pm UTC](https://discourse.processing.org/t/p3d-formula-opposite-of-screenx-and-screeny-is/10121/3 "2019-04-12T21:18:36Z")

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I was coming from this discussion

> [@Pro-Question: place a point in 3D with mouse](https://discourse.processing.org/t/pro-question-place-a-point-in-3d-with-mouse/6664/9):
>
> Ok, thanks a ton I have to look into it

I was hoping to get the opposite to screenX and screenY: think of a 3D drawing program: when I have a mouseX and mouseY and a z-value (and a previous 3D position from the previous drawing) and I wish to calculate the x,y,z position, how would I do it?

Chrisir

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