I'm talking about this : (you got it, i know x))

I would like it to look like that :

I guess I will have to use a similar technique as the one presented in this tutorial : mapping-help/tutorial-modifying-your-portal-gun-texture-t7597.html

But i don't know where the crosshair texture is...

Thank you

The file where the crosshair is stored is materials/sprites/hud/portal_crosshairs.VTF from inside your "portal 2/portal2/pak01_dir.VPK" file. The easiest approach would be to replace that file by your custom one (you could modify the hud resource file that controls this to make it point to a different file, but this is way much more complex)... However, it's a sprite sheet used by the Portal2 hud. It looks like this (but with transparent background):

Notice there are vertical division lines, you must draw whatever into each rectangle, and the game will take what's inside each one of them according to what it needs to draw at each pixel on your screen (hud).

Bare in mind the game priority as well, and introduce your new texture file into a pak01_dir.VPK file inside your portal 2/portal2_dl3 folder ok?

thank you very much !