ParticleCollision.compute

//reference: https://www.shadertoy.com/view/MsKBzD
#pragma kernel CSMain
 
RWStructuredBuffer<float4> buffer;
float iTimeDelta;
int resolution,iFrame,amount;

float3 hash( float3 p )
{
	float3 q = float3(dot(p,float3(127.1,311.7,516.3)),dot(p,float3(269.5,183.3,983.7)),dot(p,float3(419.2,371.9,679.9)));
	return frac(sin(q)*43758.5453);
}
 
[numthreads(16,16,1)]
void CSMain (uint2 id : SV_DispatchThreadID)
{   
	if (id.y < 2.0)
	{
		if (iFrame < 10) 
		{
			float3 h1 = hash(float3(id, 13.0));
			float3 h2 = hash(float3(h1 * 129.0));		
			buffer[id.y*resolution+id.x] = (id.y < 1.0) ? float4(h1.xy, (h2.yz - float2(0.5,0.5))) : float4(h1, .01 + h2.z * .01);
		}
		else 
		{
			if (id.y < 1.0) 
			{
				float4 particle = buffer[id.x]; 
				float radius = buffer[resolution+id.x].w;  
				if (particle.w < 0.0 && particle.y < radius) particle.w = -particle.w;
				if (particle.w > 0.0 && 1.0 - particle.y < radius) particle.w = -particle.w;
				if (particle.z < 0.0 && particle.x < radius) particle.z = -particle.z;
				if (particle.z > 0.0 && 1.0 - particle.x < radius) particle.z = -particle.z;
				float im0 = 1.0 / (1.33333 * 3.14159265 * pow(radius, 4.0));
				for (int i=0; i<amount; i++)
				{
					if (i == int(id.x)) continue;                   
					float4 other = buffer[i];
					float b = buffer[resolution+id.x].w;                    
					float2 d = other.xy - particle.xy;
					if (length(d) < (radius + b))
					{
						float2 n = normalize(d);  	
						float cv = dot(particle.zw - other.zw, n);
						if (cv > 0.0)
						{
							float im1 = 1.0 / (1.33333 * 3.14159265 * pow(b, 4.0));                         
							particle.zw += (n * (-2.0 * cv)) * (im0 / (im0 + im1));
						}
					} 
				}
				particle.xy += particle.zw * iTimeDelta * 0.3;
				buffer[id.y*resolution+id.x] = particle;
			}
		}
	}
}