Fade Transition

//draw the image to be transitioned to
draw_sprite(sImage2,0,0,0);

//draw the previous image with decreasing alpha
if (alpha >= 0)
{
    draw_set_alpha(alpha);
    draw_sprite(sImage1,0,0,0);
    draw_set_alpha(1.0);
    alpha -= 0.01 //change this value to adjust speed of transition.
}