gradient.py

import pygame

def fill_gradient(surface, color, gradient, rect=None, vertical=True, forward=True):
    """fill a surface with a gradient pattern
    Parameters:
    color -> starting color
    gradient -> final color
    rect -> area to fill; default is surface's rect
    vertical -> True=vertical; False=horizontal
    forward -> True=forward; False=reverse

    Pygame recipe: http://www.pygame.org/wiki/GradientCode
    """
    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
    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))