Try the following steps:

1.) Switch to orthographic projection
2.) Prepare your hud geometry
3.) Apply a vertex and fragment shader to your hud geometry
4.) Draw your triangles describing or hud geometry


When you choose your vertex shader, think about, how you would like to transform your vertices... e.g. just as linear transform e.g. applying the mere modelviewproj transform, or as non-linear transform, e.g. where you treat each vertex with a different offset vector ( computed in the vertex shader ).
Prepare the fragment shader with values per vertex to be interpolated for each fragment.

For your fragment shader, think about how you would change your fragments of your rendered hud area on screen. E.g. use interploated uv values across the triangles as input for a function for pixel color distortion ( executing inside the fragment shader ), or anything else what comes into your mind...

Try the following steps:

1.) Switch to orthographic projection
2.) Prepare your hud geometry
3.) Apply a vertex and fragment shader to your hud geometry
4.) Draw your triangles describing or hud geometry


When you choose your vertex shader, think about, how you would like to transform your vertices... e.g. just as linear transform e.g. applying the mere modelviewproj transform, or as non-linear transform, e.g. where you treat each vertex with a different offset vector ( computed in the vertex shader ).
Prepare the fragment shader with values per vertex to be interpolated for each fragment.

For your fragment shader, think about how you would change your fragments of your rendered hud area on screen. E.g. use interploated uv values across the triangles as input for a function for pixel distortion ( executing inside the fragment shader ), or anything else what comes into your mind...