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gajurgensen
gajurgensen wrote ...

2013/5/10

Need Help Handling Collisions

gajurgensen gajurgensen

2013/5/10

#
So what I am trying to do is prevent a moving object from colliding into other objects. To do this, I am trying to move it a little bit at a time. If there is a collision, it moves back. It loops through this until it either moves the whole distance it needs to in one act, or if a collision is detected and it needs to move back slightly. It sounds good in theory, but when I try to implement the idea into my code it doesn't work as expected. I have tried coding it several times and each time it has failed. This is my current code (which kind of works but far from what I was hoping for):
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private void move(){
        double stepX = 0, stepY = 0; //represents the amount that will be moved at a time, starts at 0
        if(Math.abs(xSpeed) > Math.abs(ySpeed)){ //check if xSpeed is greater than ySpeed (in terms of absolute value)
            if(xSpeed > 0)
                stepX = 1;
            else
                stepX = -1;
            stepY = stepX*(ySpeed/xSpeed); //multiplying by stepX insures that stepY is not altered by whether or not xSpeed is positive or negative
             
            for(int i = 0; Math.abs(i) <= Math.abs(xSpeed); i += stepX){
                if(getOneIntersectingObject(Actor.class)!=null){
                    setRealLocation(getRealX() - stepX, getRealY() - stepY);
                    setXSpeed(i);
                    setYSpeed((i/stepX)*stepY);
                    return;
                }
                else
                    setRealLocation(getRealX() + stepX, getRealY() + stepY);
            }
        }
        else{ //same as above but modified for if (the absolute value of) ySpeed is bigger
            if(ySpeed > 0)
                stepY = 1;
            else
                stepY = -1;
            stepX = stepY*(xSpeed/ySpeed);
             
            for(int i = 0; Math.abs(i) <= Math.abs(ySpeed); i += stepY){
                if(getOneIntersectingObject(Actor.class)!=null){
                    setRealLocation(getRealX() - stepX, getRealY() - stepY);
                    setXSpeed((i/stepY)*stepX);
                    setYSpeed(i);
                    return;
                }
                else
                    setRealLocation(getRealX() + stepX, getRealY() + stepY);
            }
        }
    }
Can anyone identify where my code is going wrong? Or perhaps it should be abandoned and I should try it from a different angle. Any advice is appreciated, thanks in advance.
danpost danpost

2013/5/10

#
Try saving the initial location of the object before the move in local fields and use a 'while' loop that sets the object to its initial location and moves the object a distance a little more than the last time through the loop, then checks for collision; if collision, break from the loop. After the loop check for collision one more time; and if collision move back to initial location and move slightly less than the last distance moved.
gajurgensen gajurgensen

2013/5/10

#
I just realized I forgot to add something to my original post. I use methods like 'setRealLocation()' and 'getRealX()' because my game scrolls, and I use 'realX' and 'realY' as my real coordinates in the game and regular x and y just as the position on the screen. Not really relevant to my problem, just to understanding the code.
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