/*
 * Copyright (c) Contributors to the Open 3D Engine Project.
 * For complete copyright and license terms please see the LICENSE at the root of this distribution.
 *
 * SPDX-License-Identifier: Apache-2.0 OR MIT
 *
 */

#include <viewsrg.srgi>

#include "SubpassInputSceneSrg.azsli"

ShaderResourceGroup SubpassInputsSrg : SRG_PerSubPass
{
    [[input_attachment_index(0)]]
    SubpassInput m_position;

    [[input_attachment_index(1)]]
    SubpassInput m_normal;

    [[input_attachment_index(2)]]
    SubpassInput m_albedo;
}

struct VSInput
{
    uint m_vertexIndex : SV_VertexID;
};

struct VSOutput
{
    float4 m_position : SV_Position;
};

VSOutput MainVS(VSInput input)
{
    VSOutput OUT;
    float2 uv = float2((input.m_vertexIndex << 1) & 2, input.m_vertexIndex & 2);
    OUT.m_position = float4(uv * 2.0f - 1.0f, 0.0f, 1.0f);
    return OUT;
}

struct PSOutput
{
    float4 m_outScene : SV_Target0;
};

PSOutput MainPS(float4 screenPos : SV_POSITION)
{
    const float3 ambient = float3(0.15, 0.15, 0.15);

    PSOutput OUT;

    float3 position = SubpassInputsSrg::m_position.SubpassLoad().xyz;
    float3 normal = SubpassInputsSrg::m_normal.SubpassLoad().xyz;
    float4 albedo = SubpassInputsSrg::m_albedo.SubpassLoad();

    // Ambient part
    const float3 lightDir = normalize(float3(-1, -1, -1));
    float3 fragcolor  = albedo.rgb * saturate(dot(lightDir, normal)) + ambient;
    
    for(int i = 0; i < NUM_LIGHTS; ++i)
    {
        // Vector to light
        float3 L = SubpassInputSceneSrg::m_lights[i].m_position.xyz - position;
        // Distance from light to fragment position
        float dist = length(L);

        // Viewer to fragment
        float3 V = position - ViewSrg::m_worldPosition;
        V = normalize(V);
        
        // Light to fragment
        L = normalize(L);

        // Attenuation
        float atten = SubpassInputSceneSrg::m_lights[i].m_radius / (pow(dist, 2.0) + 1.0);

        // Diffuse part
        float3 N = normalize(normal);
        float NdotL = max(0.0, dot(N, L));
        float3 diff = SubpassInputSceneSrg::m_lights[i].m_color * albedo.rgb * NdotL * atten;

        fragcolor += diff;
    }       
   
    OUT.m_outScene = float4(fragcolor, 1.0);
    return OUT;
}