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Traverse mipmap tree

Started by 51mon Sep 22, 2006 at 4:31 AM 1 replies 950+ views

Original Post

135

Sep 22, 2006 at 4:31 AM

I'm using a mipmap chain as a tree structure. I traverse it recursively; but here I got a problem. How much should I offset the texture coordinate for every step down the tree. I guess this picture explains it better than my words:

I'm working in directx so top-left is the filling convention. The texture coordinates goes from 0-(HalfPixel-FLT_MIN) to 1+HalfPixel and each coordinate has the range (HalfPixel >= Coordinate > -HalfPixel), the number of pixels in each level is power of two. The dimension of the top level texture (the leaf nodes) is 1024x1024 so I need 9 different offsets. Maybe someone know some article that talks about this subject? (I think I got all the numbers right)

51mon

Author

135

51mon

Sep 22, 2006 at 5:30 AM

Is it this simple:

0.5
0.25, 0.75 : Offset 0.25
0.125, 0.375, 0.625, 0.875 : Offset 0.125
...

?

AndyTX

Sep 22, 2006 at 9:41 AM

If you're storing all of your images in one texture (i.e. with a single mip level), it will depend on the arrangement that you have chosen, but gnerally you divide your local texture coordinates (i.e. where 0-1 spans the current mip level) by two, and offset by the dimension of your current mip level.

If you're using *real* mipmapping (i.e. with an attachment surface chain), then simply use LOD bias to traverse to different levels without having to change your texture coordinates at all.

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