在一个圆圈移动物体 - 机器人 [英] moving an object in a circle - android

问题描述

昨天我这个问题，我得到了一些有用的帮助，但未能解决问题。只是想我会继续努力。

I posted this question yesterday, I got some useful help but was unable to solve the problem. Just figured I'd keep trying.

确定。我试图在Android的画布上转了一圈一球的举动。做一些研究和阅读一些类似的问题后 - 我想我得到了逻辑下来，但形状保持静止。基本上我做X = A + RCOS（THETA），Y =雨（THETA）。我真的不知道是什么问题。我的code如下。有谁知道我在做什么错？我读过的其他问题，不知道为什么，我不能使它工作。

Ok. I'm trying to make a ball move in a circle on a canvas in Android. After doing some research and reading a few similar questions - I think I got the logic down but the shape remains stationary. Basically I'm doing x = a +rcos(theta), y = rain(theta). I'm not really sure what the problem is. My code is below. Does anyone know what I'm doing wrong? I've read the other questions and don't know why I can't make it work.

public class DrawingTheBall extends View {

Bitmap bball; 
int x,y, theta;


public DrawingTheBall(Context context) {
    super(context);
    // TODO Auto-generated constructor stub
    bball = BitmapFactory.decodeResource(getResources(), R.drawable.blueball);
    x = 0;
    y = 0;
    theta = 45;
}

public void onDraw(Canvas canvas){
    super.onDraw(canvas);

    Rect ourRect = new Rect();
    ourRect.set(0, 0, canvas.getWidth(), canvas.getHeight()/2);
    float a = 10;
    float b = 10;
    float r = 20;

    theta = (int) Math.toRadians(10);


    Paint blue = new Paint();
    blue.setColor(Color.BLUE);
    blue.setStyle(Paint.Style.FILL);

    canvas.drawRect(ourRect, blue);

    if(x < canvas.getWidth()){

        x = (int) (a +r*Math.cos(theta));
    }else{
        x = 0;
    }
    if(y < canvas.getHeight()){

        y = (int) (b +r*Math.sin(theta));
    }else{
        y = 0;
    }
    Paint p = new Paint();
    canvas.drawBitmap(bball, x, y, p);
    invalidate();
}

}

推荐答案

您必须增加 THETA 就行了：

theta = (int) Math.toRadians(10);

如果你总是在相同的角度画，你会总是吸引到同一个位置。

If you always draw at the same angle, you'll always draw to the same location.

编辑：

您可以把上面的线在构造函数，然后在的onDraw ，你可以这样做：

You could place the above line in your constructor, and then in onDraw, you could do:

theta = (theta + 0.1) % (2 * Math.PI)

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