shader about cone sight

I have a question that I want make enemy cone sight.

I found an approximate solution.But it’s Unity.
its:True Cone of Sight? Commandos - Unity Answers

So,Can someone help me implement it in UE4? I dont know shader.
Shader Code:

struct appdata { float4 vertex : POSITION; float3 normal : NORMAL; }

struct v2f { float4 uvShadow : TEXCOORD0; float4 uvFalloff : TEXCOORD1; float4 pos : SV_POSITION; float3 norm : NORMAL; };

v2f vert (appdata i) { v2f o; o.pos = mul (UNITY_MATRIX_MVP, i.vertex); o.uvShadow = mul (_Projector, i.vertex); o.uvFalloff = mul (_ProjectorClip, i.vertex); o.normal = i.normal; return o; }

`fixed4 frag (v2f i) : SV_Target
{
fixed4 texS = tex2Dproj (_ShadowTex, UNITY_PROJ_COORD(i.uvShadow));
texS.a = 1.0-texS.a;
fixed4 texF = tex2Dproj (_FalloffTex, UNITY_PROJ_COORD(i.uvFalloff));

 fixed4 res;
 // assume Y is up
 if(dot(i.normal, float3(0,1,0)) >= 0.9) {
     res = lerp(fixed4(1,1,1,0), texS, texF.a);
 } else {
     res = texS;
 }

 return res;

}`

Not sure about the shader code, but a similar effect can be achieved with decals.

You can also take a look at projection mapping here:
https://forums.unrealengine.com/development-discussion/rendering/103582-projection-mapping-technique-to-projects-video-files-on-objects?130980-Projection-Mapping-technique-to-projects-video-files-on-objects=