[Gear VR] Mobile HDR kills performance - why ?

[motorsep]

Just turning on mobile HDR in UE4 cuts fps (almost) in half. That's without having any post process effects on.

Why is that ? 

Thanks

[Norman3D]

I assume it consumes far more texture bandwith due to the amount of downsamples for the bloom effect for example. Wouldn't it benefit memory greatly to have one single downsample as opposed to having 3 downsamples? We don't seem to have much scalability with the current implementation.

[motorsep]

imperativity said:

Hi,

This is because HDR consumes far more texture bandwidth than the regular pipeline.

Is there any way to have bloom/glow without HDR ? (and without faking it with transparent billboards, since it's performance taxing anyway)

[motorsep]

imperativity said:

Bloom will require extra per-pixel work that will slow performance considerably on Gear VR. There are methods to fake this, but they generally require post effects or impostors and won't be fast.

Wouldn't it be much faster to do "cheap" bloom as post process?

Or something like this http://http.developer.nvidia.com/GPUGems/gpugems_ch21.html This kind of effect doesn't require HDR.