//Approach script by Matt Thorson (http://mattmakesgames.com/)
//example:
//horizontal_speed = approach(horizontal_speed, MAX_HORIZONTAL_SPEED, acceleration);

/*
APPROACH
0 - start point
1 - end point
2 - max change

Returns 0 shifted toward 1 by 2, without crossing 0.
Note that if argument2 is negative, you will move AWAY from 0.
Ex:
approach( 5, 0, 2 )     = 3
approach( -5, 0, 2 )    = -3
approach( 1, 0, 1 )     = 0
approach( 1, 0, 2 )     = 0
*/

if ( argument0 < argument1 )
    return min( argument0+argument2, argument1 );
else
    return max( argument0-argument2, argument1 );