Why was the visibility of objects in 3d Viewport restricted to a cone form? I intended to select objects with "Selection group" tool, so in order to achieve that:


pressed B hotkey with Alt or Ctrl or Shift button;
moved mouse to form rectangular area.


As a result it removed everything what was outside of rectangular area, forming infinite rectangular pyramid with it's tip on the position of my viewport when I was looking from when making selection. I can rotate around that pyramid now, where only objects (their parts) fitting that rectangular area are visible.

How can I cancel it to see all my objects back? Esc doesn't work.
Don't know what was that, but I think I fixed it:


View -> Toggle Quad View

... objects visibility was still restricted to lie within that pyramid, but it was visible from 4 different sides
View -> Toggle Quad View (again)

... can see everything now