#pragma kernel BuildMesh

#include "MathUtils.cginc"

struct RendererData
{
    float4 color;
    float radiusScale;
};

StructuredBuffer<int> particleIndices;

StructuredBuffer<float4> positions;
StructuredBuffer<float4> orientations;
StructuredBuffer<float4> radii;
StructuredBuffer<float4> colors;

StructuredBuffer<int> rendererIndices;
StructuredBuffer<RendererData> rendererData;

RWByteAddressBuffer vertices;
RWByteAddressBuffer indices;

uint firstParticle;
uint particleCount;

[numthreads(128, 1, 1)]
void BuildMesh (uint3 id : SV_DispatchThreadID) 
{
    unsigned int i = id.x;

    if (i >= particleCount) return;
    
    int p = particleIndices[firstParticle + i];
    int r = rendererIndices[firstParticle + i];

    // <<2 = multiply by 4 to get byte address, since a float/int is 4 bytes in size.
    
    // particle data is the same for all 4 vertices:
    for (uint v = i*4; v < i*4 + 4; ++v)
    {
        int base = v*23;
        
        // pos
        vertices.Store4(base<<2, asuint(float4(positions[p].xyz, 1)));

        // color:
        vertices.Store4((base+7)<<2, asuint(colors[p] * rendererData[r].color));
        
        // b1, b2, b3:
        vertices.Store4((base+11)<<2, asuint( float4(rotate_vector(orientations[p],float3(1,0,0)),radii[p].x * radii[p].w * rendererData[r].radiusScale) ));
        vertices.Store4((base+15)<<2, asuint( float4(rotate_vector(orientations[p],float3(0,1,0)),radii[p].y * radii[p].w * rendererData[r].radiusScale) ));
        vertices.Store4((base+19)<<2, asuint( float4(rotate_vector(orientations[p],float3(0,0,1)),radii[p].z * radii[p].w * rendererData[r].radiusScale) ));
    }

    //different offset for each vertex:
    int base = i*4;
    vertices.Store3((base*23 + 4)<<2, asuint(float3(1,1,0)));
    vertices.Store3(((base+1)*23 + 4)<<2, asuint(float3(-1,1,0)));
    vertices.Store3(((base+2)*23 + 4)<<2, asuint(float3(-1,-1,0)));
    vertices.Store3(((base+3)*23 + 4)<<2, asuint(float3(1,-1,0)));

    // indices:
    indices.Store((i*6)<<2, asuint(i*4+2));
    indices.Store((i*6+1)<<2, asuint(i*4+1));
    indices.Store((i*6+2)<<2, asuint(i*4));

    indices.Store((i*6+3)<<2, asuint(i*4+3));
    indices.Store((i*6+4)<<2, asuint(i*4+2));
    indices.Store((i*6+5)<<2, asuint(i*4));
}