ATAN2根据xy坐标计算角度

float centerX = v.getX() + (float) v.getWidth() / 2;
                    float centerY = v.getY() + (float) v.getHeight() / 2;
                    double angle = Math.atan2(touchRawY - centerY, touchRawX - centerX) * 180 / Math.PI;
                    v.setRotation((float) angle - 45);

                    // scale
                    float xx = (touchRawX >= centerX ? deltaRawX : -deltaRawX);
                    float yy = (touchRawY >= centerY ? deltaRawY : -deltaRawY);
                    float sf = (v.getScaleX() + xx / v.getWidth() + v.getScaleY() + yy / v.getHeight()) / 2;
                    v.setScaleX(sf);
                    v.setScaleY(sf);

/**
     * Returns the angle theta from the conversion of rectangular
     * coordinates ({@code x}, {@code y}) to polar
     * coordinates (r, theta).
     * This method computes the phase theta by computing an arc tangent
     * of {@code y/x} in the range of -pi to pi. Special
     * cases:
     *

• If either argument is NaN, then the result is NaN.
  *
• If the first argument is positive zero and the second argument
  * is positive, or the first argument is positive and finite and the
  * second argument is positive infinity, then the result is positive
  * zero.
  *
• If the first argument is negative zero and the second argument
  * is positive, or the first argument is negative and finite and the
  * second argument is positive infinity, then the result is negative zero.
  *
• If the first argument is positive zero and the second argument
  * is negative, or the first argument is positive and finite and the
  * second argument is negative infinity, then the result is the
  * {@code double} value closest to pi.
  *
• If the first argument is negative zero and the second argument
  * is negative, or the first argument is negative and finite and the
  * second argument is negative infinity, then the result is the
  * {@code double} value closest to -pi.
  *
• If the first argument is positive and the second argument is
  * positive zero or negative zero, or the first argument is positive
  * infinity and the second argument is finite, then the result is the
  * {@code double} value closest to pi/2.
  *
• If the first argument is negative and the second argument is
  * positive zero or negative zero, or the first argument is negative
  * infinity and the second argument is finite, then the result is the
  * {@code double} value closest to -pi/2.
  *
• If both arguments are positive infinity, then the result is the
  * {@code double} value closest to pi/4.
  *
• If the first argument is positive infinity and the second argument
  * is negative infinity, then the result is the {@code double}
  * value closest to 3*pi/4.
  *
• If the first argument is negative infinity and the second argument
  * is positive infinity, then the result is the {@code double} value
  * closest to -pi/4.
  *
• If both arguments are negative infinity, then the result is the
  * {@code double} value closest to -3*pi/4.

     *
     *

The computed result must be within 2 ulps of the exact result.
* Results must be semi-monotonic.
*
* @param y the ordinate coordinate
* @param x the abscissa coordinate
* @return the theta component of the point
* (r, theta)
* in polar coordinates that corresponds to the point
* (x, y) in Cartesian coordinates.
*/
@FastNative
public static native double atan2(double y, double x);