Rendering part of a plane

[Imagyx]

Hi.
I'm using the 4 functions from
http://www.iquilezles.org/www/articles/distfunctions/distfunctions.htm

When using "Intersection" with ""Sphere - signed - exact" and "Plane - signed - exact" I get  only the part of the sphere intersecting the plane.
But it doesn't work with "Box - signed - exact". I get nothing out of it.
Why ?
Box and Plane are visible and definitively intersecting, when rendering both.
And the sphere with the same 'radius' as the cube works... 

Thank you for any hint 

[claude]

works for me 

see attached...

[Imagyx]

Isn't this part of a box, therefore 3-dimensional ? I just want a part of the plane, which is 2-dim...
Maybe I misunderstood something, because after doing some tests, it seems that with
intersecting box and plane I get one of the two parts of the box, which is cut by the plane.
And these tests also revealed, that it's the same with a sphere, I just didn't see it before by chance.
Example picture here:

[claude]

in the distance estimation,  the "plane" is really a half-space, which is solid on one side.

the problem with truly 2D things in 3D distance-estimation is that they have 0 thickness, which means rendering algorithms can error by going straight through them or require adjusting fudge factors to make everything thicker.

maybe you really want a double-sided plane with a small thickness, which could be made by intersecting two opposing parallel half-spaces that are close together (but not coincident).

[Imagyx]

Thank you very much, claude  
Thickness is indeed needed for the DE to work and
your suggestion to intersect two half-spaces works for me.
I can make the Plane much thinner than it is in the video (see below)
and project an image onto the plane which is why I even needed a plane and not a simple box where the image would be wrapped around.
Have a nice weekend. With this I definitely have mine