what the....

gistfile1.m

    double direction_x = 0.0, direction_y = 0.0, direction = 0.0;
    CGPoint d = CGPointMake(current.x - previous.x, current.y - previous.y);

    if(d.x != 0) {
        if(current.y <= kCenterY) {
            if(d.x > 0.0) {
                direction_x = 1.0;
            } else {
                direction_x = -1.0;
            }
        } else {
            if(d.x > 0.0) {
                direction_x = -1.0;
            } else {
                direction_x = 1.0;
            }
        }
    }

    if(d.y != 0) {
        if(current.x <= kCenterX) {
            if(d.y > 0.0) {
                direction_y = -1.0;
            } else {
                direction_y = 1.0;
            }
        } else {
            if(d.y > 0.0) {
                direction_y = 1.0;
            } else {
                direction_y = -1.0;
            }
        }
    }
    
    direction = abs(current.y - kCenterY) > abs(current.x - kCenterX) ? direction_x : direction_y;