KisFastMath Namespace Reference

Functions
KRITAIMAGE_EXPORT qreal	atan2 (qreal y, qreal x)
	atan2 replacement

Detailed Description

This namespace contains fast but inaccurate version of mathematical function.

Function Documentation

atan2()

qreal KisFastMath::atan2	(	qreal	y,
		qreal	x )

atan2 replacement

Definition at line 68 of file kis_fast_math.cpp.

{
 
    if (y == 0.0) { // the line is horizontal
        if (x >= 0.0) { // towards the right
            return(0.0);// the angle is 0
        }
        // toward the left
        return qreal(M_PI);
    } // we now know that y is not 0 check x
    if (x == 0.0) { // the line is vertical
        if (y > 0.0) {
            return M_PI_2;
        }
        return -M_PI_2;
    }
    // from here on we know that neither x nor y is 0
    if (x > 0.0) {
        // we are in quadrant 1 or 4
        if (y > 0.0) {
            // we are in quadrant 1
            // now figure out which side of the 45 degree line
            if (x > y) {
                return(calcAngle(x, y));
            }
            return(M_PI_2 - calcAngle(y, x));
        }
        // we are in quadrant 4
        y = -y;
        // now figure out which side of the 45 degree line
        if (x > y) {
            return(-calcAngle(x, y));
        }
        return(-M_PI_2 + calcAngle(y, x));
    }
    // we are in quadrant 2 or 3
    x = -x;
    // flip x so we can use it as a positive
    if (y > 0.0) {
        // we are in quadrant 2
        // now figure out which side of the 45 degree line
        if (x > y) {
            return(M_PI - calcAngle(x, y));
        } return(M_PI_2 + calcAngle(y, x));
    }
    // we are in quadrant 3
    y = -y;
    // flip y so we can use it as a positive
    // now figure out which side of the 45 degree line
    if (x > y) {
        return(-M_PI + calcAngle(x, y));
    } return(-M_PI_2 - calcAngle(y, x));
}

References calcAngle(), and M_PI.