mip map cross-level interference?

[shuipi]

I create a 4 level mip chain(down to 1/8 on each side) of the render target every frame, however I don't just store the downscaled render result into each mip level, for levles 1, 2, 3, I also blur them before storing them to the corresponding mip levels of the texture. Next a shader access this mipmaped and blurred render result, and uses tex2Dbias to access different mip levels depending on each pixel's properties. I found a strange behavor: when a pixel is guarrenteed to be lerping betwen levels 2 and 3, whether blur level 1 will affect the result. But in theory the hardware does the trilinear lerp only between levels 2 and 3, and it shouldn't matter even if the 1st and 0th levels are garbage data, isn't that correct?

 

[Humus]

Correct. If you're indeed sampling between 2 and 3, the other levels should have no effect on the result.

 

[shuipi]

Ah, it's my code forgetting reset the bias texture state. Never mind. Sorry for confusion.