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Depth texture linearization banding on Mali 400

Stephane Jacoby
Note: This was originally posted on 19th June 2013 at http://forums.arm.com

Hello Mali devs,

We are working on an application that performs depth buffer based post processing effects, mainly for fog. We are using 24bit depth for the main scene. However when sampling this depth, the results are very banded (see attachment) due to the non linear nature of the depth buffer and Mali400's mediump 0-1 precision (2^-10 I believe). With most depth values lying in the 0.96-1.0 range, the precision is obviously insufficient. Are there any workarounds that would allow use to leverage the non fractional range of mediump floats? I suspect there isn't however wanted to make sure as the platform does provide depth24 and depth texture extensions. The option of vertex based fogging is an alternative, however, we hope to stay away from that due to the added global cost of the technique.

Many thanks,

Stephane
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  • Arm Employee Badge
    Note: This was originally posted on 1st July 2013 at http://forums.arm.com

    Always worth a couple of footnotes to the "Mali-T600 family can do highp" ...

    * Mali-T600 can do highp in the fragment shader and is very good at it, but mediump may well be faster / lower power / lower memory bandwidth (doubling the size of the vector elements and memory access size isn't free ;P).
    * Remember most content has orders of magnitude more fragments than vertices - if you can "get away with" doing the work in the vertex shader it may well give better overall performance.

    HTH,
    Iso
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  • Arm Employee Badge
    Note: This was originally posted on 1st July 2013 at http://forums.arm.com

    Always worth a couple of footnotes to the "Mali-T600 family can do highp" ...

    * Mali-T600 can do highp in the fragment shader and is very good at it, but mediump may well be faster / lower power / lower memory bandwidth (doubling the size of the vector elements and memory access size isn't free ;P).
    * Remember most content has orders of magnitude more fragments than vertices - if you can "get away with" doing the work in the vertex shader it may well give better overall performance.

    HTH,
    Iso
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