Re: Tiling several textures on one model
From: RonHiler (rhiler_at_rjcyberware.com)
Date: 07/18/04
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Date: 17 Jul 2004 23:20:04 -0700
"GuitarBill" <GuitarBill_at_cox_dot_net> wrote in message news:<ukO4z8FbEHA.2388@TK2MSFTNGP11.phx.gbl>...
> For a sphere, your normals would be = vertex position normalized (assuming
> sphere is centered on origin).
Ah, of course. I feel a little stupid now :) I didn't think about it
in those terms (I was trying to derive it in terms of Phi and Theta).
Thanks.
>
> For SpacePod (http://www.spacepod-game.com) we mapped the earth with 13
> 256x256 textures, based on Fuller projection. I wish we had gone to 512x512,
> which would have looked better... although still not enough for you (we are
> basically constant distance from earth). This would have been about 13Mb.
> I would tend to assume 384Mb is way too much - I would aim for 256Mb
> absolute tops and preferably no more than 128 or even 64 (Note: 13 textures
> at 1024x1024 would be 52Mb).
> Using this method does mean mapping the textures semi-manually (certainly
> quite a pain to get everthing to match up correctly).
Well, I'd love to bring it down, but I don't think I can. I tried the
next level down (8192 x 4096) and it looked awful. I think I'm stuck
with 16384 x 8192 equivelent. Even at that level, when the user zooms
all the way in, it starts getting more pixellated than I'd like.
This particular part will be, by far, the biggest memory hog in the
program. As long as it works, though, I'm okay with that, because
this is arguably also the most *important* part of the program.
Everything else kind of revolves around this map.
>
> If you are mapping cylindrically you are essentially wasting a lot of
> texture memory - there will be much more detail at the poles than near the
> equator. The geosphere/Fuller type projection gives more-or-less constant
> texel size across the sphere.
I'm using a Mollweide projection to store the map data (it runs 30.6
MB with 6 bytes per map point). That is then converted to a Lambert
projection (first using a 2x interpolation to bring the overall
Mollweide data to the proper size, and then stretching individual rows
until they are the proper width) to create the bitmaps. You're right,
there is a lot of wasted texture space around the poles, but what can
you do? I need a rectangular projection to create bitmaps from :)
>
> Because its a sphere, you will presumably only ever see less than half the
> sphere at any one time - an argument for not using a single texture, and
> also for using some kind of pseudo-homogeneous mapping method (wherever you
> look from you get similar memory/cache performance).
>
Hmmm, perhaps doing some quick visibility checks before drawing each
tile? You are right, in my game, only a very tiny portion of the map
will be visible at any given time. That'd save a LOT of texture
swaping.
Ron
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