java - 如何逆时针旋转 Canvas android一圈

Question

我无法解决问题，我需要帮助。我创建了围绕太阳旋转的行星，我需要一颗行星逆时针旋转，我的问题就开始了。我尝试一切我熟悉的事情。我是初学者，这是简单的代码，但我无法解决它。请帮忙。提前致谢。

我尝试逆时针旋转，只是加上减号，但这不起作用。我尝试使用半径和角度，但没有成功。我在代码中某个地方失败了，但我不知道在哪里。

...

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    screenDimensions = getDisplayDimensions();

    Bitmap bitmap = Bitmap.createBitmap(1200, 2000, Bitmap.Config.ARGB_8888);
    bitmap.eraseColor(Color.parseColor("#FFFFFF"));
    canvas = new Canvas();
    canvas.setBitmap(bitmap);

    paint = new Paint();
    paint1 = new Paint();
    paint2 = new Paint();
    paint3 = new Paint();
    paint4 = new Paint();

    paint.setColor(Color.YELLOW);
    paint1.setColor(Color.RED);
    paint2.setColor(Color.BLUE);
    paint3.setColor(Color.BLACK);
    paint4.setColor(Color.MAGENTA);


    imageView = findViewById(R.id.imageView3);
    imageView.setImageBitmap(bitmap);

    timer = new Timer();
    timer.schedule(new TimerTask() {
        @Override
        public void run() {
            runOnUiThread(
                    new Runnable() {
                        @Override
                        public void run() {
                            animationFrame();

                        }
                    }
            );
        }
    }, 2000, 80);


}

private int[] getDisplayDimensions() {
    DisplayMetrics displayMetrics = new DisplayMetrics();

    getWindowManager().getDefaultDisplay().getMetrics(displayMetrics);
    int width = displayMetrics.widthPixels;
    int height = displayMetrics.heightPixels;
    return new int[]{width, height};
}

private void animationFrame() {

    canvas.drawColor(Color.parseColor("#EBEBEB"));

    paint.setColor(Color.YELLOW);
    canvas.drawCircle(500f, 750f, 130f, paint);


    if (paint1 != null | paint3 != null) {

        paint1.setColor(Color.RED);
        canvas.drawCircle(400f, 560f, 51f, paint1);
        canvas.rotate(10f, 500f, 750f);


        paint3.setColor(Color.BLACK);
        canvas.rotate(30f, 500f, 750f);
        canvas.drawCircle(350f, 1050f, 45, paint3);


    }
    if (paint2 != null | paint4 != null) {

        paint2.setColor(Color.MAGENTA);
        canvas.rotate(-10f, 500f, 750f);
        canvas.drawCircle(720f, 950f, 48, paint2);

        paint4.setColor(Color.GRAY);
        canvas.rotate(-25f, 500f, 750f);
        canvas.drawCircle(290f, 330f, 42, paint4);

    }

    imageView.invalidate();
}

}

...

我预计其中一颗行星会逆时针旋转。

Answer 1

编辑

这段代码非常适合我:

在你的例子中，rotationPoint是太阳的中心点，bodyCenter是行星的中心点。

最终点 cx 和 cy 是行星绕太阳旋转后的中心点。

    class Vector {
        float x;
        float y;

        Vector(float x, float y){
            this.x = x;
            this.y = y;
        }
    }

    public Vector getRotatedPoint(boolean isClockwise, float rotation, Vector bodyCenter, Vector rotationPoint){
        float sin = MathUtils.sin(rotation * MathUtils.degreesToRadians);
        float cos = MathUtils.cos(rotation * MathUtils.degreesToRadians);
        float xSin = (bodyCenter.x - rotationPoint.x) * sin;
        float xCos = (bodyCenter.x - rotationPoint.x) * cos;
        float ySin = (bodyCenter.y - rotationPoint.y) * sin;
        float yCos = (bodyCenter.y - rotationPoint.y) * cos;
        float cx, cy;
        if (isClockwise) {
            //For clockwise rotation
            cx = rotationPoint.x + xCos + ySin;
            cy = rotationPoint.y - xSin + yCos;
        } else {
            //For counter clockwise rotation
            cx = rotationPoint.x + xCos - ySin;
            cy = rotationPoint.y + xSin + yCos;
        }
        return new Vector(cx, cy);
    }

要使用它，您必须先调用该方法，然后画一个圆

Vector newCenter = getRotatedPoint(true, 10f, planetCenter, sunCenter)
canvas.drawCircle(newCenter.x, newCenter.y, 48, paint2);