Basic approach is to add HLSL types FLWCScalar, FLWCMatrix, FLWCVector, etc. Inside shaders, absolute world space position values should be represented as FLWCVector3. Matrices that transform *into* absolute world space become FLWCMatrix. Matrices that transform *from* world space become FLWCInverseMatrix. Generally LWC values work by extending the regular 'float' value with an additional tile coordinate. Final tile size will be a trade-off between scale/accuracy; I'm using 256k for now, but may need to be adjusted. Value represented by a FLWCVector thus becomes V.Tile * TileSize + V.Offset. Most operations can be performed directly on LWC values. There are HLSL functions like LWCAdd, LWCSub, LWCMultiply, LWCDivide (operator overloading would be really nice here). The goal is to stay with LWC values for as long as needed, then convert to regular float values when possible. One thing that comes up a lot is working in translated (rather than absolute) world space. WorldSpace + View.PrevPreViewTranslation = TranslatedWorldspace. Except 'View.PrevPreViewTranslation' is now a FLWCVector3, and WorldSpace quantities should be as well. So that becomes LWCAdd(WorldSpace, View.PrevPreViewTranslation) = TranslatedWorldspace. Assuming that we're talking about a position that's "reasonably close" to the camera, it should be safe to convert the translated WS value to float. The 'tile' coordinate of the 2 LWC values should cancel out when added together in this case. I've done some work throughout the shader code to do this. Materials are fully supporting LWC-values as well. Projective texturing and vertex animation materials that I've tested work correctly even when positioned "far away" from the origin.
Lots of work remains to fully convert all of our shader code. There's a function LWCHackToFloat(), which is a simple wrapper for LWCToFloat(). The idea of HackToFloat is to mark places that need further attention, where I'm simply converting absolute WS positions to float, to get shaders to compile. Shaders converted in this way should continue to work for all existing content (without LWC-scale values), but they will break if positions get too large.
General overview of changed files:
LargeWorldCoordinates.ush - This defines the FLWC types and operations
GPUScene.cpp, SceneData.ush - Primitives add an extra 'float3' tile coordinate. Instance data is unchanged, so instances need to stay within single-precision range of the primitive origin. Could potentially split instances behind the scenes (I think) if we don't want this limitation
HLSLMaterialDerivativeAutogen.cpp, HLSLMaterialTranslator.cpp, Preshader.cpp - Translated materials to use LWC values
SceneView.cpp, SceneRelativeViewMatrices.cpp, ShaderCompiler.cpp, InstancedStereo.ush - View uniform buffer includes LWC values where appropriate
#jira UE-117101
#rb arne.schober, Michael.Galetzka
[CL 17787435 by Ben Ingram in ue5-main branch]
Add A flag bUseLowQualityCompression to BaseColor_Normal_Roughness, which fakes compression by 16bit format(RGB565)
#rb Dmitriy.Dyomin
[CL 16977982 by yangke li in ue5-main branch]
Fixes precision issues raised by a number of licensees (for example UDN558460).
#jira none
#rb none
#ROBOMERGE-SOURCE: CL 12237042 in //UE4/Release-4.25/... via CL 12237054
#ROBOMERGE-BOT: RELEASE (Release-4.25Plus -> Main) (v664-12234175)
[CL 12239488 by jeremy moore in Main branch]
This adds an aditional 8 bit "mask" channel for generic use in RVT materials.
[FYI] Robert.Osborne
#ROBOMERGE-SOURCE: CL 10376418 via CL 10376623 via CL 10376632
#ROBOMERGE-BOT: (v594-10333955)
[CL 10377559 by jeremy moore in Main branch]
Default to world space normals when writing to virtual texture through standard material attributes
Will require shader change for impacted materials, but almost all of our current VT materials use the VT output node and so are unaffected
This is necessary ground work for channel selection when writing to runtime virtual textures
#ROBOMERGE-SOURCE: CL 9746080 via CL 9746836 via CL 9747019
#ROBOMERGE-BOT: (v542-9736015)
[CL 9747167 by jeremy moore in Main branch]
Also touch the relevant shader to force recompile
#jira
[CODEREVIEW] Mickael.Gilabert
#ROBOMERGE-SOURCE: CL 9449112 via CL 9449598 via CL 9449613 via CL 9450296 via CL 9450439
#ROBOMERGE-BOT: (v495-9448618)
[CL 9452131 by jeremy moore in Main branch]
This allows storage of world space normals if required
[FYI] Robert.Osborne
#ROBOMERGE-SOURCE: CL 8433385 via CL 8441057
#ROBOMERGE-BOT: (v404-8404397)
[CL 8443191 by jeremy moore in Main branch]
Better normal quality then BC1+BC3
Old layout kept for now in a deprecated enum. Will probably remove after any comparisons are carried out.
#ROBOMERGE-SOURCE: CL 8288591 via CL 8288894
#ROBOMERGE-BOT: (v401-8057353)
[CL 8288898 by jeremy moore in Main branch]
Add very simple debug shading mode to runtime virtual texture
Will extend to other modes later
#ROBOMERGE-SOURCE: CL 8126086 via CL 8131842
#ROBOMERGE-BOT: (v401-8057353)
[CL 8156543 by jeremy moore in Main branch]
Remove unused height pins from RVT material nodes
Change default name of RuntimeVirtualTextureVolume actor
Integrated from //UE4/Dev-Rendering
#rb none
#rnx
#ROBOMERGE-SOURCE: CL 7049434 in //UE4/Release-4.23/...
#ROBOMERGE-BOT: RELEASE (Release-4.23 -> Main) (v367-6836689)
[CL 7049483 by jeremy moore in Main branch]
