Shader problem to distort the final render result

Hi everyone

I am working on a project and recently I have a problem:

Problem: I want to distort the final render scene of my camera. There is bunch of Shaders out there that add some effects like blur on final scene. My problem is that I want to distort the image like below picture (transposing rectangular view to trapezium shape):

Solution:

I have found a solution for my problem, and I just placed on a plane in front of camera and wrote a shader to grab the texture of screen and I implemented a simple function to do it. When I ran my application, it worked very well but in some angles didn’t work because I am using this code in VR. Finally I ended up adding this shader to the main camera, but it does not work at all.

Question: Right now, I am looking for a solution to transpose rectangular view to trapezium view without extra object like that plane. I want to add a shader to the camera itself and get the above result. Could you help me?