How can I get the default X display depth?

["simon.zheng" <Simon Zheng Sun COM>]

Hi Guys,

I failed to get display depth by gdk_rgb_get_visual().

1. I set my X display as depth 8.
#xdypinfo | grep depth
depth of root window:    8 planes

2.Then, I create a new pixmap on 8-bit using the code,
pixmap = gdk_pixmap_new (drawable, width, height,
gdk_rgb_get_visual()->depth);

Strangely, I find the value returned by gdk_rgb_get_visual()->depth is
always 24, NOT 8. I'm using gnome 2.6 and gtk+-2.4.9 on solaris. Who
know how can I get correct default depth? 

Thanks,
-Simon