drawCircle

void drawCircle(bool filled = true)(float cx, float cy, float radius, int num_segments) {
    float theta = 2 * PI / cast(float) num_segments;
    float c = cos(theta);
    float s = sin(theta);
    float t;
    float x = radius;
    float y = 0;

    static if(filled) {
        float lastX;
        float lastY;

        glBegin(GL_TRIANGLES);
        for(int i = 0; i <= num_segments; i++) {
            t = x;
            x = c * x - s * y;
            y = s * t + c * y;

            if(i > 0) {
                glVertex2f(cx + lastX, cy + lastY);
                glVertex2f(cx + x, cy + y);
                glVertex2f(cx, cy);
            }

            lastX = x;
            lastY = y;
        }
        glEnd();
    } else {
        glBegin(GL_LINE_LOOP);
        for(int i = 0; i < num_segments; i++) {
            glVertex2f(cx + x, cy + y);

            t = x;
            x = c * x - s * y;
            y = s * t + c * y;
        }
        glEnd();
    }
}