Here’s a method for ‘fog of war’ from an old Unity project. This is the kind used in games like XCOM where the world geometry outside the visible range of your units is darkened, but still at least partially visible.
I added a circle mesh (an extremely short cylinder will also work) to the player unit prefab with a radius the same as the units view radius. The circle is on its own layer (UnitViewDistance), and is textured with a radial gradient going from white to transparent black.
I added a camera (UnitViewCamera) with a depth of 0 (all other cameras are depth 1, so UnitViewCamera renders first). UnitViewCamera’s culling mask is set so that it only renders the UnitViewDistance layer, and it renders into a RenderTexture created in code. The result of all this is a transparent image with various white blobs, something like this:
The RenderTexture is then plugged into a shader and used as a mask. The intensity of the mask texel is used to lerp the colour of the final texel between full colour (at 1) and desaturated (at 0):
fixed4 frag (v2f i) : SV_Target
{
fixed4 col = tex2D(_MainTex, i.uv);
float bwCol = col.r*.3 + col.g*.59 + col.b*.11;
fixed4 maskCol = tex2D(_viewTex, i.uv);
float maskIntensity = maskCol.r;
col = lerp(bwCol, col, maskIntensity);
return col;
}
Here’s a screenshot of a programmer-art world demonstrating the (very subtle) effect – the unit is off-screen to the bottom-right, so you can see the cubes desaturating towards the top-left:
