MegaTexture Uncovered!!!

(PBMax) #1

MegaTexture == ClipMapping(or ClipTexture)

in short, its a very enhanced or “virtual” MipMapping technique developed (i think) by silicon graphics (sgi).

sgi paper from 1996!:

even better description from sgi’s developer library:
http://techpubs.sgi.com/library/tpl/cgi-bin/getdoc.cgi?coll=0650&db=bks&srch=&fname=/SGI_Developer/Perf_PG/sgi_html/ch15.html

another really good sgi paper:
http://www.cs.virginia.edu/~gfx/Courses/2002/BigData/papers/Texturing/Clipmap.pdf

the doom3 engine references many of the same concepts:
r_showMegaTexture //display all the level images
r_showMegaTextureLabels //draw colored blocks in each tile
r_megaTextureLevel //draw only a specific level
r_skipMegaTexture //only use the lowest level image

an sgi example:

This image used ClipTexture to drape 0.5m image data onto an Active Surface Definition terrain with 5m elevation data.

this HAS to be it. i wonder if this technique was patented by sgi??? i hope sgi doesn’t pull a creative labs on carmack! :stuck_out_tongue:

(Ifurita) #2

Nice find. I understood none of it, but nice find.

(EB) #3

^^^That’s the line that made me go “whoa ?!”^^^^

I will read up on it though. Thanks.

(killmachine) #4

me too :smiley: … but i think its in a very general way:

there is one huge texture, but the engine splits the texture into several smaller textures, kind of … so, u see a very detailed surface of the texture right in front of u and less detailed surfaces that are far away from u … on ur hd its one texture but the engine splits it into smaller chunks, depending on ur pov … its kind of the mipmap level but its not the mipmap thats rendered but the actual resulution of the texture …

i hope thats kinda right …

the same method is applied to all other objects too i guess … for example the polygons, the “lod” which is actually a pretty old but very good method …

(Sick Boy) #5

^^^That’s the line that made me go “whoa ?!”^^^^

I will read up on it though. Thanks.[/quote]

Maybe he meant 0.5MB and 5MB ? In which case it makes sense to me :smiley:

(Loffy) #6

pull a creative labs
Expand please, since Im always interested in behind the scenes-stories in the gaming industry.

(killmachine) #7

short story, the method of the shadow calculation in doom3 was invented by creative labs … they had problems with that, software patent … … and now in the latest patch there is creative eax support … :smiley:

(DG) #8

edit: ^ he’s more right - http://www.theinquirer.net/?article=17525

(MindLink) #9

For people who want more up to date information :

go to
http://research.microsoft.com/~hoppe/

and read the paper called “Terrain rendering using GPU-based geometry clipmaps”

Basically it’s an implementation of the stuff but instead of texturing it’s used for terrain-lod.