base.py 文件源码

def to_png(self, data, output):
        ''' Dump data to the image file. Data is bytes(RGBRGB...RGB).
            Pure python PNG implementation.
            http://inaps.org/journal/comment-fonctionne-le-png
        '''

        p__ = pack
        line = self.width * 3
        png_filter = p__('>B', 0)
        scanlines = b''.join(
            [png_filter + data[y * line:y * line + line]
             for y in range(self.height)])

        magic = p__('>8B', 137, 80, 78, 71, 13, 10, 26, 10)

        # Header: size, marker, data, CRC32
        ihdr = [b'', b'IHDR', b'', b'']
        ihdr[2] = p__('>2I5B', self.width, self.height, 8, 2, 0, 0, 0)
        ihdr[3] = p__('>I', crc32(b''.join(ihdr[1:3])) & 0xffffffff)
        ihdr[0] = p__('>I', len(ihdr[2]))

        # Data: size, marker, data, CRC32
        idat = [b'', b'IDAT', compress(scanlines), b'']
        idat[3] = p__('>I', crc32(b''.join(idat[1:3])) & 0xffffffff)
        idat[0] = p__('>I', len(idat[2]))

        # Footer: size, marker, None, CRC32
        iend = [b'', b'IEND', b'', b'']
        iend[3] = p__('>I', crc32(iend[1]) & 0xffffffff)
        iend[0] = p__('>I', len(iend[2]))

        with open(output, 'wb') as fileh:
            fileh.write(magic)
            fileh.write(b''.join(ihdr))
            fileh.write(b''.join(idat))
            fileh.write(b''.join(iend))
            return

        err = 'Error writing data to "{0}".'.format(output)
        raise ScreenshotError(err)