[x3d-public] PBR > freewrl experience

[Michalis Kamburelis]

Many, many thanks for this work, and for writing a detailed report
summarizing the implementation experience. This is great! Very
valuable to me, and I'm sure to other implementors too. And I'm very
happy that you got these results so quickly (16 days for PBR rendering
implementation is very quick, IMHO :) ).

I looked at your code and I only noticed one thing:
https://sourceforge.net/p/freewrl/git/ci/develop/tree/freex3d/src/lib/scenegraph/Component_Shape.c
calls "baseColorTexture", but the node field should be just
"baseTexture". This naming (without additional "Color" in the middle)
looks a bit simpler, and is consistent with CommonSurfaceShader too.

Regards,
Michalis

czw., 19 mar 2020 o 16:03 GPU Group <gpugroup at gmail.com> napisał(a):
>
> My experience implementing some of the PBR v4 features in freewrl:
> - took 16 days
> - I started by defining the PhysicalMaterial, UnlitMaterial and extending the Material node fields, using Michalis's documetation.
> https://github.com/michaliskambi/x3d-tests/wiki/X3D-version-4:-New-features-of-materials,-lights-and-textures#new-x3dmaterialnode-node-with-emissive-and-normalmap-textures
> - and internally extended structs in program and shader to hold all the new fields
> - then most of the 2 weeks was getting the information flowing to the shader without breaking current functionality,
> -- appearance.backMaterial - I spent a few days harmonizing TwoMaterialShader and this new approach
> -- for the texture maps I found there ware lots of issues with old code assuming certain scenarios, and I spent about a week refactoring messy old code
> - I found the khronos glTF sample had some interesting hints beyond physical, for example they use getter() functions in frag code that hides/abstracts the issue of whether or not there's a texture map.
>
> https://github.com/KhronosGroup/glTF-Sample-Viewer/tree/master/src/shaders
>
> - see the metallic-roughness.frag
>
> normal = getNormal();
>
> And I refactored the frag shader to use getters like they do.
>
> - I spent a few extra hours reading up on normal maps (which I learned are in 'tangent space' so need a transform matrix called TBN applied):
>
> https://learnopengl.com/Advanced-Lighting/Normal-Mapping
>
> - normal map normals are expressed in tangent space
>
>
> Once I had getters, and had all the info flowing to the frag shader, then it only took a few days to do the metalic-roughness functionality.
>
> If you have a loop where you are applying the lights, you probably have something like:
>
> diffuse += ...
>
> specular +=
>
> ambient +=
>
> inside the loop.
>
> For metalic-roughness, I found I could replace those 3 with
>
> shade = getPointShade(pointToLight, materialInfo, normal, view);
>
> from the khronos example to make a PBR equivalent light loop.
>
>
> So in hindsight, it would have been easy to start with the scalar PhyscialMaterial fields, and I could have added the texturemaps to the getters() later.
>
> For those implementing for GLES < 3.0 where texture units are in short supply, the scalar part of PhysicalMaterial should be no problem.
>
>
> I still have some minor tinkiering to do -when to apply gamma or its inverse, Michalis has given some answers. And field naming, textureTransform/textureCoordinate 'channel' field conventions, and I haven't attempted EnvironmentLight.
>
> Results:
>
> 1) PBR physics based rendering via PhysicalMaterial node
>  - the lighting equations use roughness and metallic with baseColor
> - (instead of specular, shininess and diffuseColor)
> - and constrain to physics principle of 'conservation of energy'
> http://dug9.users.sourceforge.net/web3d/tests/PBR/screenshot_pbr_teapots_view3dscene_freewrl.jpg
> http://dug9.users.sourceforge.net/web3d/tests/PBR/metallic_roughness.x3dv
>
> 2) extended Material node - supports texture maps for normals, emissive, diffuse, specularShininess, ambient
> http://dug9.users.sourceforge.net/web3d/tests/PBR/screenshot_e_mat_sphere240_view3dscene_freewrl.jpg
> http://dug9.users.sourceforge.net/web3d/tests/PBR/sphere_240_fw.x3dv
>
> The PhysicalMaterial node also supports texturemap for metallicRoughness although I haven't tested.
>
> 3) UnlitMaterial - roughed in plumbing but haven't tested thoroughly - should work and support normal and emissive texture maps
>
> freewrl code samples:
> https://sourceforge.net/p/freewrl/git/ci/develop/tree/freex3d/src/lib/opengl/Compositing_Shaders.c
> L.1106 MaterialInfo and gamma functions from Khronos glTF example
> L.1155 getNormal() and getter() farm starts
> L.1300-1340 getting ready for apply_lights_physical
> L.1806 apply_lights_physical code with khronos glTF sample functions, followed by freewrl light loop calling shade = pointShade(...) L.1917
>  https://sourceforge.net/p/freewrl/git/ci/develop/tree/freex3d/src/lib/scenegraph/Component_Shape.c
> L.1417 compile_PhysicalMaterial - organizes into internal structs and flags for sending to shader
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