Multisampling: performance hit if disabled?

Oldtimer
Posts: 834
Joined: 2002.09
Post: #1
Just a quick question: if I request a pixel format with multisampling capabilities, but do not use them, will rendering to that pixel format give me a performance hit even if GL_MULTISAMPLE_ARB is disabled?

The reason I'm asking is because it would be very convenient to be able to request a multisampling pixel format in all cases, but only turn it on if I'm on the "high quality" rendering path.
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Member
Posts: 446
Joined: 2002.09
Post: #2
I'm pretty sure once you get a multisample pixel format you'll see a performance hit regardless if GL_MULTISAMPLE_ARB is disabled (at least in my tests that's the case). You need to trash the context and set things up from scratch without multisampling to really "disable" it, however, there is an ATI-only extension to toggle FSAA at any time without mucking with pixel formats.
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Luminary
Posts: 5,143
Joined: 2002.04
Post: #3
Even if you disable it, Radeon 8500-9200 can't actually turn it off, so you need to do the two-context thing.
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Member
Posts: 446
Joined: 2002.09
Post: #4
This technote reaffirms both replies: http://developer.apple.com/qa/qa2001/qa1268.html (near the bottom).
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Member
Posts: 87
Joined: 2006.08
Post: #5
Don't create all your pixelformats with multisampling.

Apart from having to deal with renderers like the GMA950 which don't do MSAA at all, your allocated rendering surfaces will always consume the extra memory.

Burning 2x/4x/16x the VRAM for your framebuffer, when you're not even using the extra capacity us going to hurt.
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Oldtimer
Posts: 834
Joined: 2002.09
Post: #6
Makes sense. Thanks for the insight, everyone.
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