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Shader variable types do's and don'ts

Discussion in 'PSM' started by NFeelone, Jan 21, 2015.

  1. NFeelone

    NFeelone

    Joined:
    Oct 25, 2014
    Posts:
    3
    The official PowerVR documentation says that you have to use float, everywhere, where it's possible to make operation without convertion.
    But i found a post , where you can see a clear example the clear example, that sometimes it's better to use another type, then float

    So I ask to share some expirience about using variable types in shaders, who already do dosens of "what if"
     
    NFeelone, Jan 21, 2015
    #1

  2. eriQue

    eriQue

    Unity Technologies

    Joined:
    May 25, 2010
    Posts:
    595
    Hi,

    First of all - the post you refer to doesn't seem to account for the TBDR architecture of PowerVR.
    Drawing overlapping opaque quads will result in the GPU discarding non-visible quads, and that will skew the numbers.

    More over - using fixed4 can sometimes be a bad idea performance-wise (especially with regards to swizzling).
    In fact - HLSLSupport.cginc (part of the global includes shipped with Unity) will redefine fixed to half for non-GLSL/non-PSSL (i.e. also for PSM).

    And finally - converting between precision formats can be costly (i.e. mixing half and float).

    Some additional tips can be found here : http://docs.unity3d.com/Manual/SL-ShaderPerformance.html
     
    eriQue, Jan 21, 2015
    #2