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Archive Notice: This thread is old and no longer active. It is here for reference purposes. This thread was created on an older version of the flipcode forums, before the site closed in 2005. Please keep that in mind as you view this thread, as many of the topics and opinions may be outdated.

May 06, 2005, 06:56 AM

hello again.

I want to create an OpenGL-RC running on a graphics board that is ..

(!) running a desktop-independent display (= is not controlled by the window manager).

In the past using CreateDC() on display devices directly (skipping window creation) used to result in memory-DCs (addressing the software-implementation of OpenGL that is shipped with Windows) which lack of hw-acceleration ..

Yippadee, has anybody tried something like that before?


Erik Faye-Lund

May 07, 2005, 06:26 PM

this will be really really slow if possible at all on any AGP-system. the agp-bus is designed for fast cpu -> vram accesses, not the other way around. pci-express would solve this problem, but there are many other issues involved. so, if you need the data in system memory, either use the sw-implementation, or tolerate low speed (glReadPixels might be enough if speed is not an issue). i think also there IS some offscreen-rendering-support in wgl, but i doubt it'd be hardware accellerated.


May 11, 2005, 07:52 AM

Actually, i want the data in vram (maybe my sentences where unclear). I just doubt that windows will give me a HW-accelerated OGL-RC (the OGL-implementation of the driver) for a DC that is not meant to do output to the desktop anyway..


May 11, 2005, 09:57 AM

Isn't that decision up to the graphics driver ? I mean, why wouldn't Windows give me a HW GLRC if, say, my ATI card supported it ?

I think that any GLRC requests are passed to the vendor-specific OpenGL ICD first, and if it rejects the request, the Microsoft ICD jumps in and provides a software GLRC.

So isn't the real question: what does your graphics board's driver do ?


May 11, 2005, 10:25 AM

ok, i will stop to bother telling the system how to do what it's going to do .. :) ..and just see if it works.

thanks for now

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