Hi everyone, hope you will help me to understand this issue.
in fact what i was searching for is bump mapping in houdini , so after some searching and tests, i got confused …
because i created a burlap material directly from the material palette and inside it i just replaced the displacement vex node with a bump map node
the render result still looked like a displacement though (the edges of the geometry didn't keep unchanged), then i entered inside that bumo map node
and i found there is a displacement node inside .
can anyone please explain to me displacement vs bump in houdini ? and clarify things about what i did?

Best Regards

You can do this in several ways:
*/ Just use displacement shaders, and then turn off “True Displacements” (a Rendering Parameter available from the gear menu in your Mantra ROP, or Properties SHOP). Many of the Materials in the Palette have this exposed on their Propeerties tab - except, I see, the Burlap material. You can add it your in this case.
*/ Use the DisplaceAlongNormal nodes in the Surface Shader VOP context and ignore the movement of P, just use the new normal.
*/ Use the Bump Map VOP in the Surface Shader VOPnet, which outputs N for you to shade with.
*/ or simply perturb N in that manner of your choosing, in a Surface Shader VOPnet.

thank you a lot jason for the thourough explanation, in fact after i played a little more with it i discovered that i can jsut disconnect the P, but the true displacement flag is much simpler thanks for that tip.
i have two more questions though :
1 - what is the difference(s) between the bump map node and the displace along normal node
2 - what are the pros and cons of disconnecting the P in a displacement shader (with N still connected), or connecting the N in a surface shader ? at first i thought it would be more efficient in the surface shader or am i wrong here ?

Cheers