o3de-atom-sampleviewer/Shaders/Instanced.azsl

#include <Atom/Features/SrgSemantics.azsli>
#include <viewsrg.srgi>

struct CubeTransform
{
    float4 m_worldPosition; //XYZ world pos; ignore W
    float4 m_rotation;      //Quaternion
};

struct PerChunk
{
    uint m_chunkIndex;
};

// RootConstantBuffer<PerChunk> g_RootConstants;  // we don't support RootConstantBuffer

ShaderResourceGroup GlobalInstancedSrg : SRG_PerObject
{
    StructuredBuffer<CubeTransform> g_CubeTransforms;
}

struct VSInput
{
    float3 m_position : POSITION;
    float4 m_color : COLOR0;
    
    uint m_instanceId : SV_InstanceID;
};

struct VSOutput
{
    float4 m_position : SV_Position;
    float4 m_color : COLOR0;
};

float3 RotatePositionByQuaternion(float3 pos, float4 quat)
{
    float3 t = 2 * cross(quat.xyz, pos);
    return pos + quat.w * t + cross(quat.xyz, t);
}

VSOutput InstancedVS(VSInput vsInput)
{
    VSOutput OUT;
 
    uint chunkIndex = 0;
    CubeTransform transform = GlobalInstancedSrg::g_CubeTransforms[vsInput.m_instanceId + chunkIndex];
 
    float3 objectPos = RotatePositionByQuaternion(vsInput.m_position, transform.m_rotation);
    float3 worldPosition = objectPos + transform.m_worldPosition.xyz;
    
    OUT.m_position = mul(float4(worldPosition, 1.0), ViewSrg::m_worldToClipMatrix);
    OUT.m_color = vsInput.m_color;
    return OUT;
}

struct PSOutput
{
    float4 m_color : SV_Target0;
};

PSOutput InstancedPS(VSOutput vsOutput)
{
    PSOutput OUT;
    OUT.m_color = vsOutput.m_color;
    return OUT;
}