Cone of Sight (FOR PLAYER, NOT FOR ENEMY)?

Hello,

I have been searching for something that might help me in my case it is cone of sight for the player character, unlike the common issue cone of sight for enemies and detecting if player is within the cone of sight.

I will start off with some basic information about the game we are developing:

The game is 3D but the main camera is on 45 degrees above the player. The camera is following the player. We are trying to implement a cone of sight for the player's character, where he is able to see in front of him (the sight is represented as a cone obviously), however if there is an obstacle within the cone of sight it should block the sight behind. On top of that, we would like to have the area outside the cone of sight to be heavily distorted, which means not being rendered, but keeping the visualisation of what was seen before. A short explanation might help: Walking down a hallway seeing some enemies and objects patrolling, then you move your eyesight away, saving the things that you have previously seen on their last position you spot, saving them in a blurry way. The areas where you have not discovered (seen) yet to be completely black until you discover them.

I have searched for so long for cone of sight but to no avail. Also this new thing that we want to implement with saving the last position of something seen in a blurry way is something that I havent seen yet to be discussed.

Any help will be appreciated even I am willing to offer a small amount of money to be helped!

Thank you in advance.