Think you mean simple zooming... Here you go:
Code:
function zoom()
{
    if(key_w)
   { 
     camera.arc -=time_step*15;
   }
   if(key_s) 
   {
     camera.arc +=time_step*15;
   }
   camera.arc = clamp(camera.arc,30,80); // play with 30 and 80
}

Call this function inside the player while loop. Hope could help laugh Good luck

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