| Math.cos( ) Method | Flash 5; can be used when exporting Flash 4 movies |
| compute the cosine of an angle | | Arguments - theta
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An angle, in radians (not degrees), normally in the range of 0 to 2 , although any angle will suffice, as cosine is a periodic function. Returns The cosine of theta (the result is in the range of -1.0 to 1.0). Description The cos( ) function returns the trigonometric cosine of an angle. In a right triangle, the cosine of an angle is the result of dividing the length of the side adjacent to the angle by the triangle's hypotenuse. Usage Note that cos( ) expects angles to be provided in radians, not degrees. Exampletrace (cos(0)); // Displays: 1.0 trace (cos(Math.PI)); // Displays: -1.0 The cos( ) function can be used along with sin( ) to calculate a point on a circle, which we use in the following example to move a movie clip in a circular path. Given the radius of a circle, r, and an angle, xxxthetaxxx, measured counterclockwise from the positive horizontal axis, a point's location is (r*cosxxxthetaxxx, r*sinxxxthetaxxx): // Global Function: degreesToRadians() // Converts degrees to radians. There are 2*pi radians per 360 degrees. _global.degreesToRadians = function (degrees) { return (degrees/180) * Math.PI; } // Method: MovieClip.moveInCircle() // Desc: Starts moving the clip around a circular path. // Params: radius Radius of circle path. // x Horizontal center of circular path. // y Vertical center of circular path. // degPerFrame Number of degrees to move per frame rendered. MovieClip.prototype.moveInCircle = function (radius, x, y, degPerFrame) { var deg = 0; // Angle of object in degrees, measured // counterclockwise from the horizon (X-axis). // Assign a movement function to run once per frame. this.onEnterFrame = function () { // Increase the rotation angle by 5 degrees deg += degPerFrame; // Place the object. Note that Flash inverts the Y-axis of Cartesian // coordinates so we decrement y to obtain our new location. var rotAngRad= degreesToRadians(deg); this._x = x + Math.cos(rotAngRad) * radius; this._y = y - Math.sin(rotAngRad) * radius; } } // Usage: ball_mc.moveInCircle(100, 200, 200, 5); See Also Math.acos( ), Math.PI, Math.sin( ), Math.tan( ) |
