What is the default roughness if nothing is plugged into the material?
Like, I know specular defaults to 0.5, but what about roughness?
Thanks!
I’m not 100% sure, but I think the default roughness has a value of 1 
Pretty sure the default is 0.5
Ahh, yep that’s true -> with a value of 1 you wont have a specular effect so it must be 0.5 :o
Yes you have. That would break energy conservation. Look how bright spot gets dimmer but also bigger. And even with roughness of 1 it’s still there.
https://docs.unrealengine/latest/images/Engine/Rendering/Materials/PhysicallyBased/roughness_nonmetal.png
A bit of additional info for any fellow travelers who ended up here looking for the default roughness values…
As said 4 years ago, roughness is 0.5 by default. The definition for roughness’s default value and the default vales of other material attributes are defined in Engine\Source\Runtime\Engine\Private\Materials\MaterialShared.cpp.
As of today in the github master branch, the values are:
Add(FGuid(0x69B8D336, 0x16ED4D49, 0x9AA49729, 0x2F050F7A), TEXT("BaseColor"), MP_BaseColor, MCT_Float3, FVector4(0,0,0,0), SF_Pixel);
Add(FGuid(0x57C3A161, 0x7F064296, 0xB00B24A5, 0xA496F34C), TEXT("Metallic"), MP_Metallic, MCT_Float, FVector4(0,0,0,0), SF_Pixel);
Add(FGuid(0x9FDAB399, 0x25564CC9, 0x8CD2D572, 0xC12C8FED), TEXT("Specular"), MP_Specular, MCT_Float, FVector4(.5,0,0,0), SF_Pixel);
Add(FGuid(0xD1DD967C, 0x4CAD47D3, 0x9E6346FB, 0x08ECF210), TEXT("Roughness"), MP_Roughness, MCT_Float, FVector4(.5,0,0,0), SF_Pixel);
Add(FGuid(0xB769B54D, 0xD08D4440, 0xABC21BA6, 0xCD27D0E2), TEXT("EmissiveColor"), MP_EmissiveColor, MCT_Float3, FVector4(0,0,0,0), SF_Pixel);
Add(FGuid(0xB8F50FBA, 0x2A754EC1, 0x9EF672CF, 0xEB27BF51), TEXT("Opacity"), MP_Opacity, MCT_Float, FVector4(1,0,0,0), SF_Pixel);
Add(FGuid(0x679FFB17, 0x2BB5422C, 0xAD520483, 0x166E0C75), TEXT("OpacityMask"), MP_OpacityMask, MCT_Float, FVector4(1,0,0,0), SF_Pixel);
Add(FGuid(0x0FA2821A, 0x200F4A4A, 0xB719B789, 0xC1259C64), TEXT("Normal"), MP_Normal, MCT_Float3, FVector4(0,0,1,0), SF_Pixel);
// Advanced attributes
Add(FGuid(0xF905F895, 0xD5814314, 0x916D2434, 0x8C40CE9E), TEXT("WorldPositionOffset"), MP_WorldPositionOffset, MCT_Float3, FVector4(0,0,0,0), SF_Vertex);
Add(FGuid(0x2091ECA2, 0xB59248EE, 0x8E2CD578, 0xD371926D), TEXT("WorldDisplacement"), MP_WorldDisplacement, MCT_Float3, FVector4(0,0,0,0), SF_Domain);
Add(FGuid(0xA0119D44, 0xC456450D, 0x9C39C933, 0x1F72D8D1), TEXT("TessellationMultiplier"), MP_TessellationMultiplier, MCT_Float, FVector4(1,0,0,0), SF_Hull);
Add(FGuid(0x5B8FC679, 0x51CE4082, 0x9D777BEE, 0xF4F72C44), TEXT("SubsurfaceColor"), MP_SubsurfaceColor, MCT_Float3, FVector4(1,1,1,0), SF_Pixel);
Add(FGuid(0x9E502E69, 0x3C8F48FA, 0x94645CFD, 0x28E5428D), TEXT("ClearCoat"), MP_CustomData0, MCT_Float, FVector4(1,0,0,0), SF_Pixel);
Add(FGuid(0xBE4F2FFD, 0x12FC4296, 0xB0124EEA, 0x12C28D92), TEXT("ClearCoatRoughness"), MP_CustomData1, MCT_Float, FVector4(.1,0,0,0), SF_Pixel);
Add(FGuid(0xE8EBD0AD, 0xB1654CBE, 0xB079C3A8, 0xB39B9F15), TEXT("AmbientOcclusion"), MP_AmbientOcclusion, MCT_Float, FVector4(1,0,0,0), SF_Pixel);
Add(FGuid(0xD0B0FA03, 0x14D74455, 0xA851BAC5, 0x81A0788B), TEXT("Refraction"), MP_Refraction, MCT_Float2, FVector4(1,0,0,0), SF_Pixel);
Add(FGuid(0x0AC97EC3, 0xE3D047BA, 0xB610167D, 0xC4D919FF), TEXT("PixelDepthOffset"), MP_PixelDepthOffset, MCT_Float, FVector4(0,0,0,0), SF_Pixel);
4 Likes
This is not 100% true. Subsurface color default value is 0, not 1.