Authour: Alex 'Morgoth Bauglir' Voicu
Editor: Charles 'Lupine' Oliver
Date: April 29th, 2008
In this section we'll take a close look to a few pictures, comparing them through MS PIX's inbuilt image comparison tool by subtracting (SUB) the DX10 picture from the 10.1 one. For further testing, feel free to use XOR (exclusive OR) or XNOR (inverted XOR), but we've excluded those screenshots because, frankly, they're very hard on the eyes.
Animus Menu Comparison
Ah, the menu shot! This one has stirred quite a bit of ruckus, getting uninterested independent third-parties to analyze the shots we had included before in-depth. Unfortunately, whilst those shots were more than adequate for showing the effect DX10.1 had on AA quality, they weren't useable as a basis for overall image quality comparisons, given the fact that they were taken at slightly different angles. As a consequence, we felt obliged to fix our error, and not let the analyzing we talked about go in vain, by opening the this comparison with captures fit to be compared.
Looking at the differences underlined by MS PIX, the only notable difference is the better AA'd lower part of the visor. The DNA chain and the menu items are animated and thus the pictures grabbed them at points of their cycle, that's why they show up as different.
Acre Assassin's Office Comparison
The situation is fairly similar with the first in-game shot used, with the only notable differences being the edges that get extra AA and the animated elements in the scene, like the fountain or the GPS (Altair included: for an assassin, this guy certainly has issues standing still, and as you can see he's in a slightly different position).
Solomon's Tomb Comparison
This is where things get tricky, as alongside the usual effect of improved AA quality, we also get two other differences:
First, the 10.1 shot lacks the pillar of rising dust that's present with the earlier API. This is tied to having AA enabled, as with it disabled the dust renders just OK. Chances are that this is a driver bug, and we've already asked ATi about it-as soon as we get a reply you'll be the first to know. On the other hand, one of our (and probably everyone's) favorite developers, Emil Persson aka Humus, made a guess as to what might be happening that seems to align fairly well with what we're seeing:
"Interesting. I checked out the dust and it looks very much like itís soft particles. This means they require the depth buffer for this effect. That it doesnít work with AA makes sense too. If they simply bound the depth buffer as a texture they would need to use the Load() function rather than Sample() to fetch the depth value when itís multisampled (any single sample in the AA depth buffer should be good enough for soft shadows, no need to average). They would also need a separate shader for each AA setting, like one for 2x, 4x and 8x. I would guess itís broken because this wasnít done and they are trying to sample the MSAA buffer with Sample() using the same shader as in the NoAA / plain DX10 case. Given that the effect is quite subtle it could easily have been overlooked. So fixing this (and anything else that might be broken) is probably the reason why they said they needed to redo the DX10.1 path."
The second difference is somewhat more subtle, and it has to do with HDR lighting: with 10.1, it appears somewhat more intense. This is another behavior we've come to notice whilst going through the game (which was missed until we dwelt further into comparing the two paths). What's odd is that the way the 10.1 renders is identical to the way DX9 renders, with DX10 being the outlier. Given the fact that other GPUs display a similar pattern(DX9 being brighter than DX10), and collaborating that with UBi's statements that rendering between the paths should in theory be equal visually, it looks likely that there's actually a bug with the DX10 pathway itself, that is fixed in the 10.1 one-assuming that the way DX9 renders is the look the devs are looking for.
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