e6b124 Fix png and spritesheet render (depremultiply) by turtletooth (modified) (#1844)

5 files Authored by shun-iwasawa 6 years ago , Committed by Jeremy Bullock 6 years ago ,
    Fix png and spritesheet render (depremultiply) by turtletooth (modified) (#1844)
    
    * Fix png and spritesheet render (depremultiply)

    

    * move depremultiply in PngWriter