Flight Levels


         It's time to put on the flight goggles and get to business.
         You are a crack pilot and have been called to battle the
         forces of evil that are plaguing the planet. Double click on
         the program, and when the tower gives you approval, press "P"
         to play.
              You will quickly see a scrolling scene below your
         aircraft. The faster moving clouds are at a higher flight
         level than the slower moving ones. This is your cue to the
         correct enemy level.
              Pushing the joystick once either up or down will change
         your altitude (unless you can't go anymore). Left and right
         on the joystick will change your position on the screen. You
         can't move forward or backward, but progressively through the
         game, the forward postion is increased. This allows less and
         less reaction time to enemy that might appear.
              You will see at once an enemy craft. To shoot it down
         out of the sky, you must be at the same flight level. Fire
         your guns as soon as possible, a collision will prove deadly.
         Fortunately, you have five lives to work with.
              The game is won by flying long enough to outlive the
         enemy. The game is lost by using up all of your lives. If you
         let more than 14 enemy go by without shooting them, then you
         will lose a life. A bar at the bottom keeps track of how many
         have slipped past.
              The program was written is Laser C. Most of the graphics
         routines were written with in-line 68000 assembly. The
         airplanes were created in four colors so that only two bit
         planes had to be put onto the screen. The brown background is
         only one bit plane of data. All of the bad guys are on even
         word boundaries to avoid any bit shifting. This greatly
         increases the speed and reduces the time necessary to put
         them to the screen. All of the clouds, although on even
         boundaries, are masked to provide a transparent look.
              The screen is completely re-drawn every time that the
         objects move. This is faster than restoring a number of
         smaller areas and then redrawing them. No double buffering
         was used, but a delay loop sychronized the redraw with the
         vertical blank to avoid flicker.
              Hope you enjoy this program as much as I enjoyed writing
         it. It may be fodder for a commercial program, so you
         aspiring programmers take note.