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If you have a volume texture with mipmaps, GL_LINEAR_MIPMAP_LINEAR texture sampling will perform quadrilinear texture sampling.

Is that implemented in hardware like bilinear texture sampling is? Or does the driver just do two trilinear texture samples and interpolate those results for you?

Is trilinear sampling even supported by hardware?

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Alfonse Reinheart's post in this thread (#8) should shed some light. When you boil it down, the answer is "there's no such thing." Quadrilinear sampling is simply the term used for applying a linear sampling (GL_LINEAR_MIPMAP_LINEAR in OpenGL) to a 3D texture.

You can almost argue the answer is "yes" since linear is at the hardware level and it's simply applying several passes of linear to the texture; but strictly speaking, no.

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  • \$\begingroup\$ Thank you Stephan! You wouldn't happen to know if those lerps happen before the texture data is fed back up the pipeline do you? If possible it would be nice to verify that letting the hardware do it for you means you get the result using less resources (mostly bus bandwidth, I know that fragment shader doing the lerps is going to be more computation). \$\endgroup\$ – Alan Wolfe Jun 8 '15 at 17:16
  • \$\begingroup\$ I don't generally get that in depth with my graphics processing, but I can confidently say that letting the GPU handle any image processing is always going to be faster than kicking back to the CPU. I'm fairly confident that all the lerps would happen at once on the GPU and the result stored in the buffer, or returned up the pipe. \$\endgroup\$ – Stephan Jun 8 '15 at 17:26
  • \$\begingroup\$ In case anyone has any follow up comments in the future to further elaborate, kicking it back to the CPU definitely would be more bandwidth usage, but I'm curious about kicking it back to a fragment shader. \$\endgroup\$ – Alan Wolfe Jun 8 '15 at 17:38

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