By saying vertical gradient I meant as gradient from left to right..not from top to bottom or from b

Thank You

True the program is top to bottom or bottom to top but you can use the same logic that John Rogers used. He broke the screen down to 63 rectangles using the rectangle size as 1/63 of the screen height and the screen width. All you have to do is change the rectangle to 1/63 of the screen width and all the screen height. Fill in this rectangle with the color and add the step size to the current rectangle left.