This is a quick hack to generate gradient pngs for xfwm4 themes...

makepngs.py

#!/usr/bin/python

borders = ['bottom','bottom-left','bottom-right',
           'left','right',
           'title-1','title-2','title-3','title-4','title-5',
           'top-left','top-right']


basecolour = '#EEEEEE'


def calc_ac(x, b):
    if x == b:
        c = 0.0
        a = 0.0
    elif x < b:
        c = 0.0
        a = 1.0 - (x/b)
    else:
        a = (b - x)/(b - 1)
        c = 1.0

    return (a,c)

def calc_ac_byte(x, b):
    x = x/255.0
    b = b/255.0
    (a,c) = calc_ac(x,b)
    return (int(255*a), int(255*c))



import Image

class Xpm(object):
    def __init__(self, basename, active):
        self.basename = basename
        self.active = active
        data = open(basename+'-'+active+'.xpm')
        assert(data.next() == '/* XPM */\n')
        data.next()
        self.width, self.height, self.colours, self.pixelsize = [int(x) for x in self.strip(data.next()).split()]
        self.palette = {}
        for n in range(self.colours):
           tmp = self.strip(data.next())
           colour = tmp[0:self.pixelsize]
           self.palette[colour] = tmp[self.pixelsize:].split()
        self.pixels = []
        for n in range(self.height):
           self.pixels.append(self.strip(data.next()))

    def strip(self, line):
        return line.strip().strip(',"')

    def getpixel(self, (x,y)):
        colour = ''.join(self.pixels[y][x:x+self.pixelsize])
        return self.palette[colour][1]

    def alphadiff(self, basecolour):
        data = []
        base = int(basecolour[1:3], 16)
        for y in range(self.height):
            for x in range(self.width):
                pixel = self.getpixel((x,y))
                if pixel == 'None':
                    data.append('\x00\x00\x00\x00')
                else:
                    colour = int(pixel[1:3], 16)
                    a,c = calc_ac_byte(colour, base)
                    if base < colour:
                        data.append('\xFF\xFF\xFF'+chr(a))
                    else:
                        data.append('\x00\x00\x00'+chr(a))

        png = Image.frombytes('RGBA', (self.width, self.height), ''.join(data))
        png.save(self.basename+'-'+self.active+'.png')

    def savexpm(self, basecolour):
        f = open(self.basename+'-'+self.active+'.xpm', 'w')
        f.write('/* XPM */\n')
        f.write('static char * '+self.basename.replace('-','_')+'_'+self.active+'_xpm[] = {\n')
        f.write('"%d %d %d %d",\n' % (self.width, self.height, 2, 1))
        f.write('" \tc None",\n')
        f.write('".\tc '+basecolour+' s inactive_color_2",\n')
        for y in range(self.height):
            f.write('"')
            for x in range(self.width):
                f.write(' ' if self.getpixel((x,y)) == 'None' else '.')
            f.write('",\n')
        f.write('}\n')


def process(basename, active, basecolour):
    orig = Xpm(basename,active)
    orig.alphadiff(basecolour)
    orig.savexpm(basecolour)
    



for b in borders:
    process(b, 'active', basecolour)
    process(b, 'inactive', basecolour)