android - 在边缘反弹

Question

我正在尝试制作一个可以在屏幕上投掷硬币的小游戏。当我在寻找那种动画时，我发现了这个页面

http://mobile.tutsplus.com/tutorials/android/android-gesture/

我设法根据我的目标自定义事件，但我无法在屏幕上设置边界，以便硬币（位图）在到达边缘时会反弹。

我尝试了几次计算，但最终硬币根据边缘上的接触点奇怪地移动。

根据网站上的工作代码，有人可以帮助我吗

Answer 1

下面是我的乒乓球游戏的示例代码。每个对象都有位置 (x,y) 和它的速度。运动是应用于位置的速度。一个额外的信息是屏幕坐标系从左上角开始。Y轴下降但增加。由于屏幕坐标从 0 开始，边界变为 screen.width -1 和 screen.height -1

@Override
public void onDraw(Canvas c){

    p.setStyle(Style.FILL_AND_STROKE);
    p.setColor(0xff00ff00);




            // If ball's current x location plus the ball diameter is greater than screen width - 1, then make speed on x axis negative. Because you hit the right side and will bounce back to left.
        if((Px+ballDiameter) > width - 1){ 

            Vx = -Vx;
        }
            // If ball's current y location plus the ball diameter is greater than screen height -1, then make speed on y axis negative. Because you hit the bottom and you will go back up.
        if((Py + ballDiameter) > height - 1){

            Vy = -Vy;
        }
            // If current x location of the ball minus ball diameter is less than 1, then make the speed on x axis nagative. Because you hit to the left side of the screen and the ball would bounce back to the right side
        if((Px - ballDiameter) < 1){

            Vx = -Vx;
        }
            // If current y location of the ball minus ball diameter is less than 1, then make the speed on y axis negative. Because the ball hit the top of the screen and it should go down.
        if((Py - ballDiameter ) <1){
            Dy = 1;
            Vy = -Vy;
        }




          Px += Vx; // increase x position by speed
          Py += Vy; // increase y position by speed

        c.drawCircle(Px, Py, ballDiameter, p);



        invalidate();

}