No tangent displacement texture

Hi, I have severals problems using texture for displacement. Thanks for your help

  • d (green): why is the displacement no tangent to my mesh ? ( normals are ok, i rescaled / rotated the mesh )
  • b (blue): how can i exclude the vertex outside the image - not to affect the bump/displacement mapping ?
  • c (red) : if i dont want to affect the bottom of my mesh, i rescale small and put the wertex in a corner of my bump image. It looks ugly. Is there a better way (like in -b-)
  • a (pink) : is there a difference between “displacement” ou “bump” node ? (what is the ‘usual’ way) ?
    bump_texture.blend (2.8 MB)