test font/back for planes

    Thijs Koerselman
    May 29 2006 | 12:41 pm
    I'm rendering planes (jit.gl.gridshape) in jitter using sketch, and I want to know if I'm looking at the front or the back of a plane. Therefor I guess I need the planes normal vector and the eye vector. Are these available some way using sketch/js?
    I'd like to texture back and front differently, without rendering 2 textures and 2 planes all the time.
    -thijs
    • Wesley Smith
      May 29 2006 | 4:41 pm
      I believe you can do this with a shader and a multitextured plane. You would do something like the following.
      Vertex shader:
      use gl_Normal to compare normal direction with the eye vector and store in a varying variable
      Fragment Shader:
      use that varying variable to pick color either from Tex0 or Tex1 and assign to the fragment color.
      wes
    • Thijs Koerselman
      May 29 2006 | 6:43 pm
      thanks wes. i'll go for the shader.
      best, -thijs