Anisotropic filteringIn the list of innovations introduced by NVIDIA, the manufacturer says the 7800 features a more efficient anisotropic filtering. First important point, we have to keep in mind that because of its architecture, the GeForce 7800 GTX´s performance cost will be partially hidden with the activation of a complex filter because of a higher number of pipelines than ROPs.
But this isn’t all. NVIDIA has once again modified anisotropic filtering. It’s hard to tell what the differences are, but clearly something is new. Unfortunately, it sometimes leads to a noticeable reduction in quality in movement. We can clearly see a shimmering effect on some parts of textures, more or less obvious according to the texture level of detail, orientation, or even its level (the first is less impacted when multi-texturing). This shimmering is less noticeable with the GeForce 6800.
This utility helps to show color differences between pixels,
here level 2 textures with the 6800 and 7800. We can see that filters aren’t identical
It is impossible to show you the quality loss with a simple screenshot as it is only visible in movement. The only thing noticeable is that the texture seems less filtered and more accentuated in some areas, which causes the problem. Unfortuneatly we noticed this type of artifact on a new high end graphic card and we hope that NVIDIA will correct it.
For multi-sampling anti-aliasing, NVIDIA hasn’t changed the basic type. Once again we find the sample position introduced with the GeForce 6
, the Rotated Grid type. Our only regret here is the absence of a 6x mode supported by ATI.
NVIDIA has, however, introduced an innovating function called transparency anti aliasing. The MSAA (multi sampling anti aliasing) problem is that it doesn’t filter the interior of a texture. So when an object such as a grid or plant is represented by a texture with transparent parts, we clearly see the apparition of aliasing. A simple MSAA can do nothing about this. Only the super sampling anti aliasing helps to by-pass the problem, but this type of filter is extremely costly. It just increases the scene resolution (2048*1536 for 1024*768 for 4x !) and then applies a resizing filter.
This is where transparency anti aliasing comes in. NVIDIA hasn’t revealed all the functional details of this technology, but apparently in its super sampling mode the idea is to intelligently apply a super sampling to textures needing it, whereas the rest of the scene is still processed in multi sampling. There is also a transparency anti aliasing mode based on multi sampling, but the way it works is still unknown.
In practice, the multi sampling mode doesn’t really give satisfying results. If we look carefully at the monitor with a magnifying glass we see a slight improvement in some areas but in practice the difference is invisible. This is not a bad thing as it has nearly no effect on performance.
Without AA Transparency, then with AA Transparency MS, and finally with AA Transparency SS
The super sampling mode is very efficient, because a grid like the one here in Half Life 2 doesn’t have artifacts anymore. The performance impact is quite variable, varying from non existent for a scene without any texture to filter in this mode to being very significant when many are present. So in the Half life scene where there are many grids the frame rate drops from 104.1 to 68.2 fps. Quality has a cost and as it’s optional each user should decide if it´s worth the cost. We feel that this is an interesting initiative from NVIDIA.
This technology isn’t entirely finished, however, and we noticed a few bugs. In Half Life 2 it seems that some textures that use transparency are problematic. The shader in charge of lighting isn’t properly processed and so these textures appear white. Another problem in Far Cry, depending on the angle when looking at a plant, sometimes they are filtered and suddenly they are not. A slight move reveals this problem: