pressed a button and my model disappeared!

Hello, I was working on modeling a hairbrush and I suppose I inadvertently hit some keys and now the brush is only visible along what looks like a camera angle (the shaded bit in the below picture). The rest of the brush is there, it’s just only visible in that shaded bit. How do I change this back?

As a rule of thumb the Alt key is used for inverse operation: Ctrl+Z = Undo, Atl+Ctrl+Z= Redo. This however is only useful if you know what button you hit.
Here are some suggestions you might want to try:

  • Make a copy of your blend file and try different Alt key combinations on the copied model (undo will only work if you did not close/save Blender)
  • In the outliner check that your model is visible in the viewport (eye), selectable (cursor) and renderable (camera)
  • Does the scene render correctly => Is it a problem with the viewport or the model itself
  • Check out the particle system panel

For further help it would be useful, if you could provide the blend file.

That shaded bit makes me think that you presed ALT + B
It’s a function that allow you to make a selection and have Blender hide anything else from view, it’s still usefull in some complex model situation in which you want to focus your work on a specific zone without anything else in view (or in operation like retopo when an arm is in the way by example ) though provide no performance help (unlike the Hide function of the Sculpt mode)

If ALT+B is indeed what you did, press again ALT + B and it should get the view to normal again