You need a fixed function accessed through a shader for models. I would create a triangle model with 4 side, 2 being near 0 thick. Use one skin, the skin should be a white/ alpha noise singe image ... I.e. TGA white with the noise in the alpha channel. Last use the mtl_uvspeed / or / action fx_uvspeed from mtlFX.c

I will test moving a sprite skin without the shader as it may be possible with just the u and v members.

You are unable to change the uv members without fx_uvspeed(), You use fx_uvspeed can be called from within another action.. Sprites are fail for me, not sure why... uv memebrs should be usable without this stuff, seems total_ticks needs to be used not time_step;, Any way.

You will not be able to simply do it with a sprite.. That level of selective pixel manipulation of course would need a custom shader. However, A single sided flat triangle model and fx_uvspeed, and the trick for no_clipping will work well. One big note about the uvspeed fixed function, for me at least, it's a fps killer, if the object is not on screen, shut down the uvspeed.

Mal-