proper use of flags with gfx_drawstr to center text? (FIXED)

[clepsydrae]

If I want to center text on the screen, I'm trying:

gfx_x=gfx_w/2;
gfx_y=gfx_h/2;
gfx_drawstr("hello world", 1|4|256, 0, 0);

...but I'm clearly misinterpreting the docs. Any help? Thanks!