BILLBOARD - a tree with 2 polygons

I have made a simple tree by mapping a rgba texture on 2 crossed polygons… but those 2 polygons aren’t transparent: they’ve got the colour of the material I use :stuck_out_tongue:
how can I do to see only texels where there is the tree ?
isn’t it by using

  glAlphaFunc(GL_GREATER, 0);

just before drawing polygons ?
Is it something else to do or do I forget something important ?

I guess this NeHe Tutorial 8 explains it very well… :slight_smile: