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Mattline1

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  1. Mattline1

    PBR update

    By Mattline1,

    Main post available here
     
    I first presented my PBR work about a year ago, since then I've been tweaking and making improvements.
     
    Over the past 6 months Leadwerks has had some great updates for graphics junkies like me .The HDRi and environment probe features look great and have helped with 2 of the main issues with the last PBR system. Now what you see in the editor is what you get in the game, and HDR means proper tonemapping and a wider range of possible light intensities. Both of which are important for realistic PBR.
     
    I currently plan on using this for my current project, so expect consistent updates as I battle test it.
    The current build is available on github. Any issues and suggestions to help improve it are welcome.




     
     


    The project is available from GitHub

     
     
     
    Limitations / improvements
    Requires a gamma-correction post process shader. Not a huge issue, adding a pp is pretty easy but still something to remember.
    Currently the built in environment probes are stored in a low dynamic range. This leads to clamping and precision errors as HDR values move towards extremes. this limits the usefulness of HDR. This is an engine issue.
    Probes also use simple mipmapping for different roughness values, PBR often performs a convolution on stored cube-maps to better match reflection blurring due to roughness. A fix may be possible for this, but would require C++.

     


    </p>
  2. Mattline1
    (Wait all day for a bus and two turn up at once)
     
    As part of my final year university work I’ve been looking into Physically Based Rendering(PBR) and its implementation. PBR is a method of generating images that takes physical values into account, this means lighting behaves much more predictably and accurately.
     
     
    This link https://www.fxguide.com/featured/game-environments-parta-remember-me-rendering/ gives a fantastic, and in depth look into how PBR works in Remember Me. Notably, PBR systems aren’t all the same, often times they use different algorithms to generate images, and there are many ways to generate reflections for them.
     
    This PBR uses a runtime rendered cubemap to generate reflections and ambient diffuse lighting on objects, nice for avoiding the flat lighting in shadowed areas problem. It then uses a physically based BRDF to generate specular highlights.
     
    Currently static models and animated models have shaders, there is also preliminary decal support. All light types are supported with shadowing. The materials use metalness/roughness maps.
    There are a number of example assets in the zip files.
     
    You’ll need the C++ version of Leadwerks for this one, the reflection generation code is written in C++ and relies on a number of OpenGL calls to function properly. This does mean however that you can generate a new reflection map at any point.
     
    I was aiming for a similar system to what was used in GTAV. For that game a low poly, diffuse only environment map is generated each frame in order to render reflections. However for my work the performance isn’t quite high enough to generate a reflection map per frame yet.
     
    Reflections are generated as cube maps, that map is then sampled with GL_SEAMLESS_CUBEMAPPING enabled, the lowest mipmap is used for diffuse lighting then higher mip values are used for the specular reflections.
     
    (If you are using the lua version, you may be able to use pre-blurred cube-maps and get acceptable results)
     
    Here’s an example of the shaders working on a complex PBR asset. Built by Andrew Maximov, http://polycount.com/discussion/130641/cerberus-ffvii-gun-next-gen-asset-giveaway
     
    Without-PBR

     
    With-PBR

     
     
    I’m looking for feedback on how robust the system is, so here is a download link, you're free to use this as you please.
    https://dl.dropboxusercontent.com/u/23307723/Leadwerks_PBR.zip
     
     
    Issues
    I’ve had to use the alpha channel for gloss values so transparency is a bit borked. Decals suffer from the alpha problem as well.
    I’ve looked into binding reflection textures to the lighting shaders which would avoid the alpha hijacking. But it doesn’t seem to work if any post processing or water is used. If anyone can point me in the right direction here it would be appreciated.
     
    my implementation uses normalised Blinn-Phong for the distribution term, Schlick’s approximation for Fresnel, and Smith’s shadowing function for the geometry term.
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