ScriptableRenderPipeline/Assets/ScriptableRenderLoop/HDRenderPipeline/ShaderPass/ShaderPassVelocity.hlsl

#if SHADERPASS != SHADERPASS_VELOCITY
#error SHADERPASS_is_not_correctly_define
#endif

// Available semantic start from TEXCOORD4
struct AttributesPass
{
    float3 previousPositionOS : NORMAL; // Contain previous transform position (in case of skinning for example)

    // TODO: Caution - For now the tesselation doesn't displace along the normal with Velocity shader as the previous previous position
    // conflict with the normal in the semantic. This need to be fix!
};

struct VaryingsPassToPS
{
    // Note: Z component is not use currently
    // This is the clip space position. Warning, do not confuse with the value of positionCS in PackedVarying which is SV_POSITION and store in unPositionSS
    float4 positionCS;
    float4 previousPositionCS;
};

// Available interpolator start from TEXCOORD8
struct PackedVaryingsPassToPS
{
    // Note: Z component is not use
    float3 interpolators0 : TEXCOORD8;
    float3 interpolators1 : TEXCOORD9;
};

PackedVaryingsPassToPS PackVaryingsPassToPS(VaryingsPassToPS input)
{
    PackedVaryingsPassToPS output;
    output.interpolators0 = float3(input.positionCS.xyw);
    output.interpolators1 = float3(input.previousPositionCS.xyw);

    return output;
}

VaryingsPassToPS UnpackVaryingsPassToPS(PackedVaryingsPassToPS input)
{
    VaryingsPassToPS output;
    output.positionCS = float4(input.interpolators0.xy, 0.0, input.interpolators0.z);
    output.previousPositionCS = float4(input.interpolators1.xy, 0.0, input.interpolators1.z);

    return output;
}

#ifdef TESSELLATION_ON

// Available interpolator start from TEXCOORD4

// Same as ToPS here
#define VaryingsPassToDS VaryingsPassToPS
#define PackedVaryingsPassToDS PackedVaryingsPassToPS
#define PackVaryingsPassToDS PackVaryingsPassToPS
#define UnpackVaryingsPassToDS UnpackVaryingsPassToPS

VaryingsPassToDS InterpolateWithBaryCoordsPassToDS(VaryingsPassToDS input0, VaryingsPassToDS input1, VaryingsPassToDS input2, float3 baryCoords)
{
    VaryingsPassToDS ouput;

    TESSELLATION_INTERPOLATE_BARY(positionCS, baryCoords);
    TESSELLATION_INTERPOLATE_BARY(previousPositionCS, baryCoords);

    return ouput;
}

#endif // TESSELLATION_ON

#ifdef TESSELLATION_ON
#define VaryingsPassType VaryingsPassToDS
#else
#define VaryingsPassType VaryingsPassToPS
#endif

// We will use custom attributes for this pass
#define VARYINGS_NEED_PASS
#include "VertMesh.hlsl"

PackedVaryingsType Vert(AttributesMesh inputMesh,
                        AttributesPass inputPass)
{
    VaryingsType varyingsType;
    varyingsType.vmesh = VertMesh(inputMesh);

    // It is not possible to correctly generate the motion vector for tesselated geometry as tessellation parameters can change 
    // from one frame to another (adaptative, lod) + in Unity we only receive information for one non tesselated vertex.
    // So motion vetor will be based on interpolate previous position at vertex level instead.
    varyingsType.vpass.positionCS = mul(_NonJitteredVP, mul(unity_ObjectToWorld, float4(inputMesh.positionOS, 1.0)));
    varyingsType.vpass.previousPositionCS = mul(_PreviousVP, mul(_PreviousM, _HasLastPositionData ? float4(inputPass.previousPositionOS, 1.0) : float4(inputMesh.positionOS, 1.0)));

    return PackVaryingsType(varyingsType);
}

#ifdef TESSELLATION_ON

PackedVaryingsToPS VertTesselation(VaryingsToDS input)
{
    VaryingsToPS output;

    output.vmesh = VertMeshTesselation(input.vmesh);

    output.vpass.positionCS = input.vpass.positionCS;
    output.vpass.previousPositionCS = input.vpass.previousPositionCS;

    return PackVaryingsToPS(output);
}

#include "TessellationShare.hlsl"

#endif // TESSELLATION_ON

float4 Frag(PackedVaryingsToPS packedInput) : SV_Target
{
    FragInputs input = UnpackVaryingsMeshToFragInputs(packedInput.vmesh);

    // input.unPositionSS is SV_Position
    PositionInputs posInput = GetPositionInput(input.unPositionSS.xy, _ScreenSize.zw);
    UpdatePositionInput(input.unPositionSS.z, input.unPositionSS.w, input.positionWS, posInput);
    float3 V = GetWorldSpaceNormalizeViewDir(input.positionWS);

    // Perform alpha testing + get velocity
    SurfaceData surfaceData;
    BuiltinData builtinData;
    GetSurfaceAndBuiltinData(input, V, posInput, surfaceData, builtinData);

    VaryingsPassToPS inputPass = UnpackVaryingsPassToPS(packedInput.vpass);
#ifdef _DEPTHOFFSET_ON
    inputPass.positionCS.w += builtinData.depthOffset;
    inputPass.previousPositionCS.w += builtinData.depthOffset;
#endif

    // TODO: How to allow overriden velocity vector from GetSurfaceAndBuiltinData ?
    float2 velocity = CalculateVelocity(inputPass.positionCS, inputPass.previousPositionCS);

    float4 outBuffer;
    EncodeVelocity(velocity, outBuffer);
    return outBuffer;
}