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MadKamote

HDR with 2x FP16 MRTs question

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Hi! I saw a sample in an NVidia using MRTs in speeding up the HDR effect. They also used some other card features to speed it up like fp texture filtering and VTF's, although my concern is with the MRT part. There isn't much explanation on the NVidia paper on why this happens. I just can't get around with the idea that using 2 D3DFMT_G16R16F through MRT is faster than just using one D3DFMT_A16B16G16R16F texture. What exactly happened here? Why or how MRT speeds this process up? Also, is it safe to assume that this technique is specific only to NVidia cards and not on ATI?

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*just a guess*

G16R16F is 32bits wide compared with A16B16G16R16F being 64bits wide. Maybe it's just a simple case that their hardware can move chunks of 32bit data around more efficiently than a bigger 64bit chunk...?

Jack

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by the way, on my 6600 Go card, the hdr sample works FASTER in 1xRGBA MRT mode, NOT 2xRG. ForceWare 81.85. go figure...

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