I have an angular gradient algorithm:

GLuint OGLENGINEFUNCTIONS::CreateAngularGradient( std::vector<ARGBCOLORF> &input,POINTFLOAT start, POINTFLOAT end, int width, int height )
{
    std::vector<GLubyte> pdata(width * height * 4);
    float pi = 3.1415;
    float cx;
    float cy;

    float r1;
    float r2;
    float ang;

    float px;
    float py;

    float t;

    cx = start.x;
    cy = start.y;
    r1 = 0;
    r2 = 500;
    ang = end.x / 100;

    ARGBCOLORF color;

    for (unsigned int i = 0; i < height; i++) {
        for (unsigned int j = 0; j < width; j++) {

            px = j;
            py = i;
            if( px * px + py * py <= r2 * r2 && px * px + py * py >= r1 * r1  ) 
            {
                t= atan2(py-cy,px-cx) + ang;
                t= t+ pi;
                if (t > 2* pi)
                {
                    t=t-2*pi;
                    t=t/(2*pi);
                }

            }
            //end + start
            color.r = (0 * t) + (120 * (1 - t));
            color.g = (50 * t) + (255 * (1 - t));
            color.b = (0 * t) + (50 * (1 - t));
            color.a = (255 * t) + (200 * (1 - t));

            pdata[i * 4 * width + j * 4 + 0] = (GLubyte)  color.r;
            pdata[i * 4 * width + j * 4 + 1] = (GLubyte) color.g;
            pdata[i * 4 * width + j * 4 + 2] = (GLubyte) 12;
            pdata[i * 4 * width + j * 4 + 3] = (GLubyte) 255;
        }
    }

It works fine except the ang variable only controls the end sweep, not the start sweep. The start sweep is always facing the middle left as seen here: http://img810.imageshack.us/img810/9623/uhoh.png

Basically I have no control over the end one going this <- way. How could I control this one?

Thanks