def fill_gradient(surface, color, gradient,
                  rect=None, vertical=True, forward=True):

    if rect is None:
        rect = surface.get_rect()

    x1, x2 = rect.left, rect.right
    y1, y2 = rect.top, rect.bottom

    if vertical:
        h = y2 - y1
    else:
        h = x2 - x1

    assert h > 0

    if forward:
        a, b = color, gradient
    else:
        b, a = color, gradient

    rate = (float(b[0] - a[0]) / h,
            float(b[1] - a[1]) / h,
            float(b[2] - a[2]) / h)

    fn_line = pygame.draw.line
    if vertical:
        for line in range(y1, y2):
            color = (min(max(a[0] + (rate[0] * (line - y1)), 0), 255),
                     min(max(a[1] + (rate[1] * (line - y1)), 0), 255),
                     min(max(a[2] + (rate[2] * (line - y1)), 0), 255))
            fn_line(surface, color, (x1, line), (x2, line))
    else:
        for col in range(x1, x2):
            color = (min(max(a[0] + (rate[0] * (col - x1)), 0), 255),
                     min(max(a[1] + (rate[1] * (col - x1)), 0), 255),
                     min(max(a[2] + (rate[2] * (col - x1)), 0), 255))
            fn_line(surface, color, (col, y1), (col, y2))
Fill a surface with a linear gradient pattern.
dataset/ETHPy150Open fictorial/pygameui/pygameui/render.py/fill_gradient