gpu blend mode ext arguments

bm_zero            = 1
bm_one             = 2
bm_src_colour      = 3
bm_inv_src_colour  = 4
bm_src_alpha       = 5
bm_inv_src_alpha   = 6
bm_dest_alpha      = 7
bm_inv_dest_alpha  = 8
bm_dest_colour     = 9
bm_inv_dest_colour = 10
bm_src_alpha_sat   = 11