what is tri-linear minimapping?

[Mucman]

I heard it is a feature on Geforce cards... can anyone explain?

Thanx

 

[RoboTECH]

mipmaps are just scaled versions of the same texture, i.e. a basic 256x256 texture will look pretty silly if it's all the way across a large map, versus being right up against your face.

Therefore, they scale the texture into different "mipmaps", a 256x256 (the main one), a 128x128, a 64x64, a 32x32, etc.

Then, the textures will be rendered using the appropriate mipmap, depending upon the "distance" the texture is from you.

As you can imagine, there can be very obvious delineations where the mipmaps change. The easiest way to notice this is to stand on a large floor in a game like Quake3. Look at the floor, as the floor moves away, there will be a noticeable "line" of blurriness where it seems that there is a very definite change in texture quality. that is the mipmap line.

trilinear filtering is a method of blending mipmap delineations so that they aren't so annoying
it's somewhat effective, high-tap anisotropic filtering is another way, mipmap dithering is another way.

typically, high-tap (large # of samples) anisotropic filtering is considered "best", but comes at a hefty performance hit. The Geforce cards have a unique method of trilinear filtering which allows for trilinear to be enabled with a very minimal framerate loss. This is, IMHO, the best feature the GeForces have.

now that I'm done, watch my explanation get torn up for being technically off. <g>

 

[Mucman]

Didn't expect a response this late at night 🙂 thanks

How will this affect games when the start triple texture games? Does the Radeon have a similar feature, because I know it boasts being able to do a triple texture in one pass...

sorry if I don't have the terminology right, I am sort of a newbie when it comes down to the specs of vid cards. I just know I want a GF2 Ultra 🙂

 

[ElFenix]

we probably won't see any triple textured games, DX8 spec is quad textures. nvidia cards used to fake trilinear mipmapping.

 

[Mucman]

so triple texture was more ATI hype than anything else? And what do you mean by nvidia faked trilinear mipmapping?

 

[BFG10K]

Regarding the ATi issue, I read somewhere that the third texture unit is simply wasteful in DirectX 8. When nVidia and 3dfx do two passes with both texture units full, ATi will do one pass with all three units full and then one extra pass with only one texture unit full, and the other two texture units will be empty.

 

[Mucman]

I thought ATI was just preparing for future use of triple textures? I know it seems like a waste when running duel textures, but how are the Geforce cards going to look when doing triple textures? They will have to waste one unit while the Radeon will be 100% efficient. Please don't slag for misinterpreting numbers, I just want to understand video cards a little better so I have just started doing a little reading 🙂

and back to the original question... how will trilinear mipmapping do when it comes to games using more than duel texturing?

 

[RoboTECH]

Mucman, when games use more than duel texturing, all of today's cards are gonna get whomped.


WRT ATi's triple texture units, it helps out quite a bit when anisotropic filtering is enabled, or when enabling, for example, Dot3.

 

[ElFenix]

the DX8 spec is for quadruple texturing, which the radeon will require 2 passes to do, just like the geforce. an i dunno how exactly nvidia cards faked trilinear. i think the drivers told the game it was there and then just did bilinear.

 

[jpprod]

TNT1/2 faked trilinear mip mapping when they were in multitexturing mode. True trilinear - just as anisotropic - caused a 50% fillrate hit for TNTs, so nVidia implemented trilinear approximation into the hardware. Approximation worked by dithering mip map levels close to the border of two different resolutions instead of blending (second mip map) over the whole whole texture in true trilinear manner.

GeForce on the other hand has fillrate hit free trilinear, only cost is eight textel fetches per pixel instead of standard four. GeForce2 GTS on the other hand has to utilize both texturing units on a pixel pipeline to produce trilinear pixel. You can consider this as a step backwards or forwards, whatever you'd like: pipelines were enhanced to be able to handle two completely different textures instead of just different resolution mip maps, but trilinear textel rate per clock remained the same as on original GeForce.

 

[Mucman]

holy information overload batman!!!

I gonna have to give jpprod's explanation another read when I finish my exam 🙂...

Now I have two more questions :

Do all cards have a version of this? What does G400, or Radeon use?

And is trilinear mimmapps somehow related to projection matrices? I am learning linear algebra now and I hear about how it works hand in hand with lots of computer science stuff.