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ZealousEngine

How to edit mipmaps in photoshop?

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So I want to see if I can get a object to fade out in the distance by setting the alpha of the mipmaps on my dds texture. Think this will work? The problem is, I dont know how to access the mipmap layers. I have Photoshop 7.0 and the dds plugin from nvidias website. When I go to save a dds, I can view a "mip map preview", but is there no way to actually edit the mipmaps manually? BTW Is this how some games get grass billboards to shrink/grow based on camera distance? In anycase, editing the mipmaps manually could create some neat effects imo.

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Guest Anonymous Poster
Quote:
Original post by ZealousEngineBTW Is this how some games get grass billboards to shrink/grow based on camera distance?


I think thats called perspective...


Do you know that the DDS file has the mipmaps saved in it? maybe they are generated when you load the file..

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Quote:
Original post by Anonymous Poster
Quote:
Original post by ZealousEngineBTW Is this how some games get grass billboards to shrink/grow based on camera distance?


I think thats called perspective...


Do you know that the DDS file has the mipmaps saved in it? maybe they are generated when you load the file..


I think the effect he's talking about is how the grass quads "grow" out of the ground. This isn't a texture effect, but a positioning of the quad's vertices. They "grow" out of the ground (generally) as a LOD mechanism. If they didn't grow out of the ground, you'd notice popping. I belive it would also be less processor costly than fading in the geometry.

AP has a point, make sure the format you're using actually saves the mipmap chain in the file. It could be that the preview is just that, a preview of what is expected to be generated.

-Michael g.

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Thanks ill look into that tool. I realised this wouldnt work anyway (at least not for cross plains) because correct me if im wrong, but mipmaps are used on angled objects, not just distant ones, right? Id still like to try it with sprites though...

So when you say people 'grow' grass patches by manipulating the verts, is this done in a shader? That would mean the shader is calculating the distance (from eye) for EVERY vert in the grass patch, that seems a tad expensive.

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Mipmaps are used based off of distance only.

If you have trilinear filtering enabled, mipmaps levels *fade* from one to the next.

Anistrophic (sp?) filtering involves specially stretched maps (for those angled surfaces you were talking about) (ya know, 1/2 width, full height, full width, 1/2 height, etc...)

Summed up, on angled walls, at say, x units, (at the current texture scaling) the texture will change (bilinear + mipmap) or fade (trilinear) to the next mipmap level.
So, depending upon your question, yes, mipmaps apply to angled walls too.

I'm not sure how the anistrophic filtering generates its chain - try it out!

-Michael g.

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Hmm interesting. Well I got my grass system working (decided to use cross plains instead of sprites), now I need a way to fade the objects out in a radius around the camera. Can anyone explain how I could 'grow' my grass objects out of the ground? Seems like it would require a distance check inside the vertex shader, and if im gonna do that, I might as well just alpha fade them.

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