ZDoom

I want to made camera which show what player have behind him in the upper side of screen, like rearview mirror.
Is it possible to do so using only zscript?

I think that's totally possible. I created something extreme similar in FamiliarDoom - a little view from familiar. Check out either my code (ZScript/HUD, hud mini camera) or try to experiment with function in TexMan class You'll need to make a dummy actor which always will be at the same position as player, but looking opposite direction.

Check out the test files in this bug report.

(hopefully the bug in question will be fixed by the time you implement this)

For the angle and position you might need to have an actor that constantly follows the player and sets its angle to the player's minus 180.

...and also change camera pitch to (-player.pitch).