Two basic PBR workflows
Before adding PBR into your X-Plane objects, it’s necessary to have some rough idea on PBR workflow
There are Metal - Roughness workflow and Specular - Glossiness workflows. Both of them have three fundamental texture maps.
(pic from https://academy.substance3d.com/courses/the-pbr-guide-part2-zh)
Metal - Roughness workflow:
(0,0,0) means black and (1,1,1) means white
Metallic map(gray scale image):
- Black means Dielectrics (0,0,0) reflect less light(not accurate)
- Metals = White (1,1,1) reflect more lights(not accurate)
Roughness map(gray scale image):
- Black means smooth surface (0,0,0)
- White means rough surface (1,1,1)
Specular - Glossiness workflow:
(0,0,0) means black and (1,1,1) means white
Specular map(Gray scale image):
- black means no reflection
- white means it will reflect back
Glossiness map(gray scale image):
used to describe microsurface irregularities, essentially the inverse of the roughness map
- black means rough surface (0,0,0)
- white means smooth surface (1,1,1)
useful links that introduced the above maps
https://www.youtube.com/watch?v=pt_5QDiA-PU
https://www.youtube.com/watch?v=e9KF64hMn98
https://www.youtube.com/watch?v=DGAta2ZWokQ
https://www.youtube.com/watch?v=KyZdn5XLwfU
PBR workflow in X-Plane
according to “X-Plane 11 Material Model”
(https://developer.x-plane.com/article/x-plane-11-material-model/)
- Base reflectance (OPTIONALLY STORED IN THE BLUE CHANNEL) how much light is reflected of the surface at an orthogonal angle
no blue means no base reflectance maximum blue means a completely reflective material at all viewing angles - store Metallic map / Specular map (in blue channel of final “normal”) in this case, no base reflectance (no blue) indicates black, a completely reflection (blue) indicates white. Hence, When using Specular map, no post process is required.
An black & white colour inverse is required for Metallic map.
- roughness is stored in the alpha channel. most glossy is maximum opacity(white), 0.0(most transparent) means roughest (black)
comparison
for X-Plane,no post process is needed when using glossiness map. If using roughness map, we need to inverse Black and white colour.
Result
Base reflection:
- black means no reflection
- white means it will reflect back
roughness of a material:
- black means rough surface (0,0,0)
- white means smooth surface (1,1,1)
** In conclusion, for X-Plane(Same as specular glossiness workflow) **
Combine maps into X-Plane “normal map”
X-Plane uses only three maps for an object, day/night texture and a “Normal map”.
References
https://learnopengl.com/PBR/Theory
https://www.youtube.com/watch?v=_PPTG1waeZ8
https://www.rastertek.com/dx10tut21.html#:~:text=Specular%20mapping%20is%20the%20process,used%20for%20specular%20highlights%20instead.
https://developer.x-plane.com/article/obj8-file-format-specification/
https://forums.x-plane.org/index.php?/forums/topic/165679-specular-in-a-normal-is-the-sdk-a-riddle/
https://academy.substance3d.com/courses/the-pbr-guide-part2-zh
https://forums.x-plane.org/index.php?/forums/topic/111261-testing-xp11-material-reflections-in-scenery/
https://developer.x-plane.com/article/x-plane-11-material-model/
https://www.fsdeveloper.com/wiki/index.php?title=Normal_map_creation
https://forums.x-plane.org/index.php?/forums/topic/147572-please-help-with-normalspecular-maps-under-blender-and-gimp/
https://forums.x-plane.org/index.php?/forums/topic/129078-a-set-of-normal-maps/
https://developer.x-plane.com/article/normal-maps/
https://developer.nvidia.com/nvidia-texture-tools-exporter?tdsourcetag=s_pctim_aiomsg
https://forums.x-plane.org/index.php?/forums/topic/126048-normal_metalness-obj-file/
https://blog.teamtreehouse.com/beginners-guide-physically-based-rendering-unity#:~:text=A%20metallic%20map%20simply%20describes,you%20should%20avoid%20anything%20between.
https://www.youtube.com/watch?v=pG8OHpVUHdI
https://docs.gimp.org/2.10/en/plug-in-decompose-registered.html
https://github.com/X-Plane/XPlane2Blender/issues/357
https://www.youtube.com/watch?v=pt_5QDiA-PU
https://www.youtube.com/watch?v=e9KF64hMn98
https://www.youtube.com/watch?v=DGAta2ZWokQ
https://www.youtube.com/watch?v=KyZdn5XLwfU