触摸后连续运动？

Question

Found plenty of questions that were similar, but nothing that answers my own problem. It's probably something really bloody simple, but it's late and I can't fathom it. I've got an android game I'm working on, where you touch the screen and it 'fires' a sprite in that direction. I've got most of the code working, however, after the sprite fires and moves off, it gets to the touch point and then just wiggles. I would like it to carry on along that angle and eventually bounce around...

Here's my code (well the bits that matter):

List<TouchEvent> touchEvents = game.getInput().getTouchEvents();
        int len = touchEvents.size();

        for(int i = 0; i < len; i++) {
            TouchEvent event = touchEvents.get(i);                        
            if(event.type == TouchEvent.TOUCH_UP) {
                touchPoint.set(event.x, event.y);
                guiCam.touchToWorld(touchPoint);                               
            }
        }

        //Log.d("PANDAM", touchPoint.x + "|" + touchPoint.y);
        float speed = 112f;
        double theta = 180.0 / Math.PI * Math.atan2(panda_y - touchPoint.y, panda_x - touchPoint.x);
        Log.d("PANDAM", " > "+theta+" < ");

        movePanda(theta, speed, deltaTime);

And the "movePanda" method:

    private void movePanda(double angle, float speed, float deltaTime)
{   
    panda_x += speed * Math.cos(angle)*deltaTime;
    panda_y += speed * Math.sin(angle)*deltaTime;       
}

My question is, how do I get the panda to carry on along the touch vector and not spaz out when it reaches the original touch point?

Answer 1

You seem to be recalculating the angle each step of the animation, but you actually need to remember what the angle was when you first started moving. As you pass the original touch point, the angle changes to point the other direction, so if you reclcalculate it every animation step, it will change and eventually point the other way.