#ifndef UNITY_SHADER_VARIABLES_FUNCTIONS_INCLUDED
#define UNITY_SHADER_VARIABLES_FUNCTIONS_INCLUDED

#include "Packages/com.unity.render-pipelines.core/ShaderLibrary/SpaceTransforms.hlsl"

// Note: '_WorldSpaceCameraPos' is set by the legacy Unity code.
float3 GetPrimaryCameraPosition()
{
#if (SHADEROPTIONS_CAMERA_RELATIVE_RENDERING != 0)
    return float3(0, 0, 0);
#else
    return _WorldSpaceCameraPos;
#endif
}

// Could be e.g. the position of a primary camera or a shadow-casting light.
float3 GetCurrentViewPosition()
{
#if defined(SHADERPASS) && (SHADERPASS != SHADERPASS_SHADOWS)
    return GetPrimaryCameraPosition();
#else
    // This is a generic solution.
    // However, for the primary camera, using '_WorldSpaceCameraPos' is better for cache locality,
    // and in case we enable camera-relative rendering, we can statically set the position is 0.
    return UNITY_MATRIX_I_V._14_24_34;
#endif
}

// Returns the forward (central) direction of the current view in the world space.
float3 GetViewForwardDir()
{
    float4x4 viewMat = GetWorldToViewMatrix();
    return -viewMat[2].xyz;
}

// Returns 'true' if the current view performs a perspective projection.
bool IsPerspectiveProjection()
{
#if defined(SHADERPASS) && (SHADERPASS != SHADERPASS_SHADOWS)
    return (unity_OrthoParams.w == 0);
#else
    // TODO: set 'unity_OrthoParams' during the shadow pass.
    return UNITY_MATRIX_P[3][3] == 0;
#endif
}

// Computes the world space view direction (pointing towards the viewer).
float3 GetWorldSpaceNormalizeViewDir(float3 positionWS)
{
    if (IsPerspectiveProjection())
    {
        // Perspective
        float3 V = GetCurrentViewPosition() - positionWS;
        return normalize(V);
    }
    else
    {
        // Orthographic
        return -GetViewForwardDir();
    }
}

// UNITY_MATRIX_V defines a right-handed view space with the Z axis pointing towards the viewer.
// This function reverses the direction of the Z axis (so that it points forward),
// making the view space coordinate system left-handed.
void GetLeftHandedViewSpaceMatrices(out float4x4 viewMatrix, out float4x4 projMatrix)
{
    viewMatrix = UNITY_MATRIX_V;
    viewMatrix._31_32_33_34 = -viewMatrix._31_32_33_34;

    projMatrix = UNITY_MATRIX_P;
    projMatrix._13_23_33_43 = -projMatrix._13_23_33_43;
}

#if UNITY_REVERSED_Z
    #if SHADER_API_OPENGL || SHADER_API_GLES || SHADER_API_GLES3
        //GL with reversed z => z clip range is [near, -far] -> should remap in theory but dont do it in practice to save some perf (range is close enough)
        #define UNITY_Z_0_FAR_FROM_CLIPSPACE(coord) max(-(coord), 0)
    #else
        //D3d with reversed Z => z clip range is [near, 0] -> remapping to [0, far]
        //max is required to protect ourselves from near plane not being correct/meaningfull in case of oblique matrices.
        #define UNITY_Z_0_FAR_FROM_CLIPSPACE(coord) max(((1.0-(coord)/_ProjectionParams.y)*_ProjectionParams.z),0)
    #endif
#elif UNITY_UV_STARTS_AT_TOP
    //D3d without reversed z => z clip range is [0, far] -> nothing to do
    #define UNITY_Z_0_FAR_FROM_CLIPSPACE(coord) (coord)
#else
    //Opengl => z clip range is [-near, far] -> should remap in theory but dont do it in practice to save some perf (range is close enough)
    #define UNITY_Z_0_FAR_FROM_CLIPSPACE(coord) (coord)
#endif

#endif // UNITY_SHADER_VARIABLES_FUNCTIONS_INCLUDED