collision_mesh_plane.compute

//reference book: "Real-Time Collision Detection" by Christer Ericson

#pragma kernel CSMain
#pragma kernel CSInit

StructuredBuffer<float3> input;
RWStructuredBuffer<uint> output;
float4x4 ObjectToWorld;
float4 A,B,C; 

struct Plane 
{
	float3 n; 
	float d; 
};

Plane ComputePlane(float3 a, float3 b, float3 c)
{
	Plane p;
	p.n = normalize(cross(b - a, c - a));
	p.d = dot(p.n, a);
	return p;
}

float DistPointPlane(float3 q, Plane p)
{
	return dot(q, p.n) - p.d; 
}

[numthreads(8,1,1)]
void CSInit(uint id : SV_DispatchThreadID) 
{
	output[id] = 0; 
}

[numthreads(8,1,1)]
void CSMain (uint id : SV_DispatchThreadID)
{
	Plane plane = ComputePlane(A.xyz,B.xyz,C.xyz);   
	float d = DistPointPlane(mul(ObjectToWorld,float4(input[id],1.0)).xyz,plane);
	uint value ;
	if (abs(d)<0.001) 
		value = 1;
	else 
		value = 0;
	InterlockedAdd(output[0], value);
}