negative sides of clipping planes?

Hi everyone,

A little trouble with clipping planes. A while Ago I asked about (naively) using them within jit.gl.sketch to affect jit.gl.gridshapes (to which jkc said this was a misuse...I apologize for this continued misuse, but I can't do all this within jit.gl.sketch). Well, I'm still at it, and I've greatly simplified what I need into something that works and seems semi-elegant, with one glaring exception: when I want the "streaks" of turning the render's erase_color to , for example, "erase_color 0. 0. 0. .1".

When I do that, it works fine if the clipping plane has all positive coefficients. But if I want to clip on the "negative" side of the plane (by turning one of the coefficients negative), I get the pure white-out of no erase_color translucency. See below for simple example.

Is there another way to define which side of a clipping plane the clipping should actually occur on? (and then be able to use all positive coefficients) or am I just missing something with the math, etc?

Thanks for any help...
Dan