dispoffset doesn't work with gr_spritebillboarding
There's a piece of code responsible for making dispoffsets work in opengl.
// if it has a dispoffset, push it a little towards the camera
if (spr->dispoffset) {
float co = -gl_viewcos*(0.05f*spr->dispoffset);
float si = -gl_viewsin*(0.05f*spr->dispoffset);
baseWallVerts[0].z = baseWallVerts[3].z = baseWallVerts[0].z+si;
baseWallVerts[1].z = baseWallVerts[2].z = baseWallVerts[1].z+si;
baseWallVerts[0].x = baseWallVerts[3].x = baseWallVerts[0].x+co;
baseWallVerts[1].x = baseWallVerts[2].x = baseWallVerts[1].x+co;
}
As you can see this doesn't have anything to do with the y-axis, which would work if it weren't for billboards.