On Sun, Dec 19, 2010 at 07:34:38PM -0700, steve harley wrote: > [subscribed from another address due to apparent blacklisting of my ISP] > > On 2010-12-19 15:28 , John Francis wrote: > > > >Way, way more than you need. > > > >For normal (non-game) use, you basically need enough video memory > >to hold a full-screen image. For a 1920x1080 display, in 24-bit > >true colour (let's call it 32-bit pixels) that's roughly 8MB. > > um, yes, Mac OS X uses 32 bits per pixel because it has an alpha > channel, but ... no, this analysis is very dated -- nowadays (at > least on Mac OS X) the GPU is a major part of the processing chain > in some uses; it makes certain operations (mainly vector and matrix > operations) much faster than when the CPU is used; on Mac OS X the > OS uses is automatically and many apps take extra steps to get a > boost from the GPU ... the benefit is strong enough, for example, > that it helps the MacBook Air, which has an NVidia GeForce 320M GPU > instead of low-performing Intel GMA GPU, perform much better than > its wimpy CPU would suggest (solid state drive helps too) > > and even if your supposition were correct (VRAM used only for > display) you'd need enough for every window, times at least two for > double-buffering; hit the Expos? button on my machine and you'll > usually see 30+ windows, not counting 80+ tabs in assorted browser > (tabs use VRAM just as windows do)
Yes, but you don't need 64 bits per pixel for a lot of windows (in fact eight bits or 12 bits can often be enough; there's no need for a dialog box, text window, editor window, etc. to be full colour double buffered if you have a decent window manager). And the amount of memory used for GPU instruction streams, data, display lists, etc. is rarely the governing factor at present in display memory usage. It's handy if you can render all application windows into VRAM, and let the window manager decide how to construct the desktop display from all the separate parts. But it isn't necessary to do so; most applications are capable of redrawing their windows if asked. In any case, the original question was about 256MB, which is going to be more than enough for just about any scenario except games with a vast amount of texturing, multi-stage rendering pipelines, etc. And, of course, there are always those applications that want more than 32 bits/pixel; image processing likes 64-bit pixels. Double buffer that, add a Z-buffer and a few overlay buffers, and you can begin using large amounts of VRAM. And Photoshop is beginning to make use of GPUs for some purposes. I'm sure that we'll soon see a version of Photoshop that can do real-time panorama stitching (with on-the-fly lens profile correction) from multiple RAW images; when that happens high-end video cards will use memory by the GB. -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
