/*
 * 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 <Atom/Features/SrgSemantics.azsli>

ShaderResourceGroup InstanceSrg : SRG_PerDraw
{
    float2 m_viewportSize;
    Texture2D m_texture;
    
    Sampler m_sampler
    {
        MaxAnisotropy = 16;
        AddressU = Clamp;
        AddressV = Clamp;
        AddressW = Clamp;
    };
};

struct VSInput
{
    float3 m_position : POSITION;
    float4 m_color : COLOR0;
    float2 m_uv : TEXCOORD0;
};

struct VSOutput
{
    float4 m_position : SV_Position;
    float4 m_color : COLOR0;
    float2 m_uv : TEXCOORD0;
};

VSOutput MainVS(VSInput IN)
{
    // Convert from screen space to clip space
    float2 posXY = float2(IN.m_position.xy) / InstanceSrg::m_viewportSize * 2.0f - float2(1.0f, 1.0f);
    posXY.y *= -1.0f;
    float4 posPS = float4(posXY, IN.m_position.z, 1.0f);

    VSOutput OUT;
    OUT.m_position = posPS;
    OUT.m_color = IN.m_color;
    OUT.m_uv = IN.m_uv;
    return OUT;
};

struct PSOutput
{
    float4 m_color : SV_Target0;
};

PSOutput MainPS(VSOutput IN)
{
    PSOutput OUT;

    float4 tex;

    tex = InstanceSrg::m_texture.Sample(InstanceSrg::m_sampler, IN.m_uv);
    float opacity = IN.m_color.a * tex.a; 

    // We use pre-multiplied alpha here since it is more flexible. For example, it enables alpha-blended rendering to
    // a render target and then alpha blending that render target into another render target
    OUT.m_color.rgb = IN.m_color.rgb * tex.rgb * opacity;

    OUT.m_color.a = opacity;
    return OUT;
};