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just a simple question

Started by smokes Jun 5, 2002 at 7:15 AM 2 replies 200+ views

Original Post

Jun 5, 2002 at 7:15 AM

Can a directdraw 7 backbuffer be in system memory? would this be a severe performance hit?.. I want to keep every surface in sysmen except the primary buffer (which of course is impossible :-).. do sys->sys blit.. and then flip.. But as I understand pageflipping is archieved by swapping vidmem pointers.. and then it won''t work if the backbuffer is in sysmem.. then it should be done with a sysmen backbuffer surface and a regular blt?.. I need to alter my backbuffer heavily for certain effects.. and reading from vidmem IS very slow.. So I should treat the vidmem as write only right?

Jason Doucette

Jun 5, 2002 at 9:45 AM

I''m programming with DirectDraw, and messing with the backbuffer by doing some reads to modify the data, as well.

Has anyone testing any of the latest video cards on how fast you can read from the video buffer, in comparison to how fast you can write to it?

Just curious. I may make a program to do this myself if no one has.

Jason Doucette
http://www.jasondoucette.com/

smokes

Jun 5, 2002 at 10:40 AM

that really answered my question Jason.. and thanks for changing the subject of my thread too ;-)

DrunkenHyena

Jun 5, 2002 at 11:51 AM

Reading from video memory is slow. If you''re doing a lot of pixel pushing, don''t do it on a video surface.

You can either write to an offscreen sysmem surface and blit to the primary (you''ll get tearing) or write to the offscreen sysmem surface and blit to a video mem backbuffer and flip.

Stay Casual,

Ken
Drunken Hyena

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