Superku

I was able to get c_trace to work properly by building on your and Rei's comments. Here is the final version:
Code:
if (c_trace (player.x, vector(player.x + 128*cos(player.pan), 
    player.y + 128*sin(player.pan), player.z + 0), IGNORE_ME | USE_BOX) > 0)
   {c_move (player, vector(0, 0, 0), nullvector, GLIDE);}
else
   {move_forward();}

Thanks again for your help.