GDK rendering under win32

[Dan McMahill <mcmahill mtl mit edu>]

Hello,

I have been involved for some time with a project written around gtk for 
graphically displaying some files that are used in the manufacture of 
circuit boards (gerbv.sf.net).

Over the last year one of our developers has added the option to use 
cairo rendering instead of the direct GDK rendering.  What we have 
observed is that under various unix-like operating systems such as linux 
or netbsd that the cairo rendering is a good bit slower (up to 8x 
slower) than GDK rendering although we lose some features like transparency.

However, building the same app on windows shows that the GDK rendering 
is much slower than the cairo rendering (as much as a factor of 3).

Just to put some example numbers out there

linux, gdk - 4 redraws/sec
linux, cairo - 0.5 redraws/sec

windows, cairo - 0.5 redraws/sec
windows, gdk  - 0.17 redraws/sec


actually we see a small difference between linux and windows, but 
ballpark, the cairo rendering is similar between the two.

So my question is if GDK rendering is known to be extremely slow under 
windows when compared to cairo or linux GDK rendering?  We're seeing 
maybe a factor of 25 difference with comparable hardware while the cairo 
difference is small.  I'm using the latest as of today versions of the 
gtk for win32 stuff (gtk+-2.14.1, glib-2.18.0, ...)

Thanks
-Dan