Hello all!
I am beta testing an unnamed online game. This game is "state of the art"
when it comes to the graphics and I have had a great deal of fun trying to
figure out how they are doing a few things. One of their outstanding
features is the quality of their terrain and one feature in particular
stands out.
As you move through the world there is a bubble around you which textures
the terrain at amazingly high detail. In most cases this is a detail
texture over a base texture, but in some cases they are doing something
else. In particular their roads have exceedingly fine detail, far beyond
most of the ground. One thing I observed is that the road textures seem to
be built so that there is no "flow" to speak of and would look good flowing
in any direction. Bricks would of course violate this rule, so I am seeing
irregular flagstones for example. Why is this important? Because the
technique I am thinking of would require that the "road" texture be tilable,
repeatable and non-directional.
1. How I don't think it is working
I do *not* beleive they are building specially built geometry on top of the
terrain. Because I see this technique applied to other terrainfeatures
needing extra detail I do not think they are building sliced-coplanar
greometry to hug the ground. I think they are re-rendering the same terrain
patch multiple times to produce a final merged texture.
2. How I think we could do it
Justin's e-mail on alpha masking got me to thinking. What if, for each pass
on the terrain patch, they combined and alpha mask with an underlying
texture? So lets say that each terrain patch 128m x 128m with a 128x128
precomputed terrain texture + detail texture (thats what Magicosm uses), Now
lets say that when you are computing the base texture and you were
calculating the road pixels, you also created an alpha mask matching the
portion of the patch where the road was. You then rendered a second pass
for that patch which combined the road texture, say 256x256 (repeated 4
times across the patch) with the alpha mask. I think you could conceivably
draw just the road against the terrain with a high level of detail.
3. Multi-pass with multi-texturing. I don't know if this would work, but my
understanding is that if you use more texture units than supported on the
card then Java3d will fall back to multi-pass. if this is true I think you
could set up 4 texture units: base texture, detail noise, high density path,
alpha mask and it would merge all 4 when it rendered.
tex unit 0=Base texture (modulate)
tex unit 1=noise texture (add signed)
tex unit 2=road texture (modulate)
tex unit 3=alpha mask
texAttr.setCombineRgbSource(2 TextureAttributes.COMBINE_OBJECT_COLOR);
texAttr.setCombineAlphaSource(3,
TextureAttributes.COMBINE_TEXTURE_COLOR);
4. Using decal group. I am not sure if this would work, but you could have
decal which used the alpha masking technique to only render over the patch,
but only overwriting and updating the non-masked part. So
First layer:
tex unit 0=Base texture (modulate)
tex unit 1=noise texture (add signed)
Second layer (decal)
tex unit 0=road texture (modulate)
tex unit 1=alpha mask
texAttr.setCombineRgbSource(0, TextureAttributes.COMBINE_OBJECT_COLOR);
texAttr.setCombineAlphaSource(1,
TextureAttributes.COMBINE_TEXTURE_COLOR);
Would either or both work? If we used the multi-pass technique how would
the combiner's be set up?
5. Fading the "bubble"
Since this high detail enchancment would only be applied to the level 0
patches surrounding the user, we need a way to to move the bubble of this
high detail as you move through the world. These patches would be rendering
far more slowly because of the extra passes, so you would not want to just
render every level 0 patch with this technique. In addition you would not
want the road "popping" in front of you as you moved, but rather to unroll
smoothly. Perhaps we could have the alpha mask texture as by-ref and modify
it at runtime each frame by masking out the edges?
Any thoughts or suggestions would be appreciated!
David Yazel
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