unreal engine 4.8 teselation problem

tessellated materials seem to be broken.
when I want to make a simple tesselated material it returns:
“warning X3206: implicit truncation of vector type”
"error x3000: unrecognized identifier ‘FVertexFactoryInterpolantsVSToDS’ "
what is problem? how can I have a tessellated object?
I have a ATI card and it supports DX11 .its not old… somehow ,is it possible that it related to DX11 ?..(maybe it’s not enabled or I don’t know …just you tell me what s problem:( )

there is no answer?:frowning:

This is not an issue with standard UE4, this is because you are using the NVIDIA merged version. There is a known issue with tessellation and Flex (since the addition of the flex fluid surface). My branch has been patched to fix this, so you can take a look and cherry pick the latest commit.