Hide some objects from the camera (fog)

Question

I'm trying to implement a visibility representation in a 2D game ( no plains, no quads - plain 2D ) In the examples below I have calculated what the player can see using raytracing and added all the colliding points as vertices to a polygon 2D collider. What is within the polygon is in view.

I want everything outside this visible area to be darker / faded out / fogged out, so that it is not visible / as visible as what is in the view. Prefably I would want to choose what objects are included in this darkening, so that static enviroment is not affected but enemy players are.

Simply deactivating the object's renderers is not an option. I also though about overlaying a texture and using a cutout alpha mask, but that would not translate well considering that the visible polygon is updated every frame and the mask has to be premade(?).

Answer 1

I also though about overlaying a texture and using a cutout alpha mask, but that would not translate well considering that the visible polygon is updated every frame and the mask has to be premade(?).

I'd consider to dynamically build a mesh with the calculated polygons and draw it before everything else. It works occluding the rest of the scene behind (either fully opaque or semi-transparent depending on you requirements).

This way you can continuously update the mesh geometry depending on how visibility changes.

Of course some CPU work is required to rebuild the mesh on every visibility change, but from the screenshots above the vertices count seems not huge (I'll instead pay attention on using tons of raycast each fram to build it).

Answer 2

From your question, I understand you need to simulate object occlusion: in real life (as well as in any 3D videogame) you just can't see an object hiding behind another bigger object. I think of an easy way to accomplish this:

• Use raytracing to detect which areas the player can or can't see from current position (that's what you did in figure 2) to simulate "distance fog";
• Use simple line collision detection from player object towards any 'actor' (enemy, object, anything you need to hide if not "seen" from the player) to test if player can actually see them or not; if there's no collision along this line (thus there is no solid geometry between player and current actor) then render the actor's graphics, else don't.

This way actors will be rendered only if their origin point lies inside the 'visible' area.

Also, if you want to limit player's sight, you can check both line collision and distance from player to make sure engine doesn't render actors beyond the circumference representing player's 'field of view'.