Scratch

I've run into this problem a number of times...what is happening is that the motion actions generated from the arrow keys are over-riding the "turn-around and walk away from the wall" command.  The best solution I've been able to come up with is to keep track of the last spot where the player wasn't touching a wall and then send the player back there if a wall is touched.  This gets around the whole "which direction is away from the wall" problem.  If you decide to go with this approach, you will find it easier if you collect all the arrow key scripts into a single loop, so all the motion is being handled in one spot.  Then, use variables to store the last spot where you weren't touching a wall.

I can make you a small demo, if you want.

I've used Paddle2See's idea, which is very robust: You store the last safe location (x1, y1). Then you move in response to user input. Then you test whether you are touching the wall. If you are, you go back to the last safe location. It's not as smooth but it's pretty foolproof.

nvm, i've solved it using your technique

Jens wrote:

It only works flawlessly with perfectly symetrical (circular) sprites, though, or if you never rotate the sprite. With rotatable excentrical sprites I prefer something like:

   (in "player" sprite):

   forever
      repeat until touching "wall"
         move ...
      end
      turn ...
      repeat until not touching "wall"
         move ... (in reverse direction)
      end
   end

This will also make for smoother movement, I guess.

The method I put forth will work with non-symetrical and rotating sprites - if your step size is greater than the largest radius your sprite will describe.  In other words, if you step back far enough, you will not be able to contact the wall regardless of the orientation of the sprite.  If necessary, you can keep track of the last safe position two moves old and go back there when you contact a wall.

Alternatively, you can keep track of the sprite orientation as well as it's position and return the sprite to it's old spot and it's old direction after contact with the wall.  This is probably the simplest approach.

I have tried various versions of the approach you suggest; the Repeat until Not Touching Wall approach, and have not had great success with it.  It is usually possible to fool it somehow by either approaching the wall diagonally, backing into the wall or rotating the sprite into the wall - which results in very strange actions.  The strange actions include quick trips through the wall or very long translations along the wall.

If you have an example of a fool-proof routine that uses your logic, I would love to see it.

Last edited by Paddle2See (2008-02-18 06:30:49)