View Full Version : anisotropic filter in opengl
03-21-2011, 05:53 AM
I need to know how anisotropic filter is implemented in OpenGL. Specifically what is the shape of the sampling filter on the texture. Is it a ellipse like EWA. Where can I find exact details about it ?. I looked at lot of resources on internet but they seem to add to the confusion.
I would wait for good pointers on this issue.
03-21-2011, 06:48 AM
The way to perform anisotropic filter is not specified in OpenGL, hardware implementers are free to do it the way they want.
Not sure about this, but they seem to prefer to keep such details for themselves as I never seen concrete info on this topic. Patents may also be a problem.
03-21-2011, 06:51 AM
Here (http://www.opengl.org/registry/specs/EXT/texture_filter_anisotropic.txt) is the specification of the extension.
03-22-2011, 12:34 AM
Thanks for the link. It is not clear what is the function tau.
03-22-2011, 03:08 AM
It is not clear what is the function tau.
Does it matter? Remember: that section is preceded by the text:
The following describes one particular approach to implementing anisotropic texture filtering for the 2D texturing case:
This section does not say that this is how it must be implemented; it only says that this is how it might be implemented. So even if you knew exactly how that suggested implementation worked, it would say precious little about what any particular hardware actually does.
Be advised that anisotropic filtering changes based on driver-related settings. Driver settings can override your aniso choices, or they can affect the specific way in which aniso works for your application.
In short, the only thing you can truly know about anisotropic filtering is that it will probably look better than standard linear-mipmap-linear minification filtering. And that higher numbers will generally help improve the quality of the result.
03-22-2011, 06:12 AM
In short, the only thing you can truly know about anisotropic filtering is that it will probably look better than standard linear-mipmap-linear minification filtering. And that higher numbers will generally help improve the quality of the result ... and increase rendering time at the same time.
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