Fillrate/Bandwidth question: 1024x768@2xMSAA/4xMSAA vs 1280x1024@0xMSAA

[tahrikmili]

Which of the two following resolutions requires more fillrate and/or bandwidth, and how do I go about calculating this?

1024x768@2xMSAA
1024x768@4xMSAA
1280x1024@0xMSAA

Sorry if this is a stupid question

P.S. Also, slightly offtopic, between 1024x768@4xMSAA and 1280x1024@0xMSAA, which do you think gives better IQ?

 

[ERK]

I'm not an expert on this, but I think calculations are difficult because you need to know how many pixels lie on a triangle edge.
EDIT: and I think most people would back off one res notch to get 4xAA. Tastes vary.

 

[sireric]

Theoretically, the number of samples per pixel will determine your bandwidth increase -- Basically, 2xMSAA should require twice the amount of BW as 0xMSAA.

However, modern gfx cards generally compress the frame buffer data when running in MSAA, so that the cost of BW is usually much lower; 2xMSAA is often close to free, while 4xMSAA is usually a reasonably low cost. But it's highly dependant on the compression algorithm used, as well as the frame being rendered. For example, a full screen quad will generally cost no more in MSAA as in non-AA cases.

As for fillrate, the typical Z hit is (1/number of samples). ATI does do better than this on current HW (2x that), but it's a good general rule, as you do have to do Z compares for all fragments. Color blending can be similar, dependant on the color compression algorithm used.

Finally, in terms of quality, it's generally subjective, but it's fair to say that 2xMSAA or 4xMSAA will look better for edges (at 10x7) than 12x10 no AA, since there are effectively many more samples involved. However, texture content will look better at 1280 than 1024, so the overall image might or might not look better. It can go either way, depending on the image displayed. Better to run at the highest resolution your monitor does well, with as much AA as you can afford, fps wise.

 

[Fox5]

With a res like 1280x1024, we're probably talking about an LCD monitor. Since the 1024x768 image would then either be bordered or stretched to fit, 1280x1024 will look better.

 

[thekey]

With a res like 1280x1024, we're probably talking about an LCD monitor. Since the 1024x768 image would then either be bordered or stretched to fit, 1280x1024 will look better.

Why would it be different on a CRT monitor? Also I own a LCD monitor: are pixels those dots you see on the screen? If so why are all turned on if Im using a 1024x768 resolution and this moitor is best viweed with 1024x768? Thanks for the answers.

 

[thekey]

I meant 1280x1024

 

[kemist]

An lcd can scale the image, so it can display lower resolutions (not higher), but the lower resolutions do not look as good as the native due to the scaling and the pixels not mapping 1:1.

 

[Reverend]

Better to run at the highest resolution your monitor does well, with as much AA as you can afford, fps wise.

I take it that you mean, basically, higher resolutions without any AA are preferred to lower resolutions with some AA, both at the same FPS, yes?

PS. Are you usually more active in the forums after you've been recently interviewed?

 

[Ailuros]

I take it that you mean, basically, higher resolutions without any AA are preferred to lower resolutions with some AA, both at the same FPS, yes?

I don't think so since the last paragraph sounded perfectly clear to me.

<snip>

Finally, in terms of quality, it's generally subjective, but it's fair to say that 2xMSAA or 4xMSAA will look better for edges (at 10x7) than 12x10 no AA, since there are effectively many more samples involved.

Here the theoretical EER for 1024 with 2x or 4x MSAA is a lot higher than in 1280, but exclusively concentrated on polygon edges/intersections.

<snip>

However, texture content will look better at 1280 than 1024, so the overall image might or might not look better. It can go either way, depending on the image displayed.

Here's where the size of the monitor and the according dpi value per resolution also factors in. If I have the dilemma between 1280/4xAA and 1600/2xAA on this 21", I'd most likely pick the latter for the above reason and in that regard I don't see anything wrong with the last sentence you quoted nor does he strictly suggest that one should skip AA entirely. Highest possible resolution with the highest possible amount of AA.

If in my example above performance shouldn't be sufficient with 2xAA in 1600, then it's more likely that even without AA it won't be that much faster.