#include "PreparedSplatView.hlsli"

cbuffer FrameConstants : register(b0)
{
    float4x4 gViewProjection;
    float4x4 gView;
    float4x4 gProjection;
    float4 gCameraWorldPos;
    float4 gScreenParams;
    float4 gSettings;
};

StructuredBuffer<PreparedSplatView> gPreparedViews : register(t0);
StructuredBuffer<uint> gOrderBuffer : register(t1);

struct VertexOutput
{
    float4 position : SV_Position;
    float4 color : COLOR0;
    float2 localPosition : TEXCOORD0;
};

VertexOutput MainVS(uint vertexId : SV_VertexID, uint instanceId : SV_InstanceID)
{
    VertexOutput output = (VertexOutput)0;
    uint splatIndex = gOrderBuffer[instanceId];
    PreparedSplatView view = gPreparedViews[splatIndex];
    float4 color = UnpackPreparedColor(view);

    if (view.clipPosition.w <= 0.0)
    {
        const float nanValue = asfloat(0x7fc00000);
        output.position = float4(nanValue, nanValue, nanValue, nanValue);
        return output;
    }

    float2 quadPosition = float2(vertexId & 1, (vertexId >> 1) & 1) * 2.0 - 1.0;
    quadPosition *= 2.0;

    float2 scaledAxis1 = view.axis1 * gSettings.w;
    float2 scaledAxis2 = view.axis2 * gSettings.w;
    float2 deltaScreenPosition =
        (quadPosition.x * scaledAxis1 + quadPosition.y * scaledAxis2) * 2.0 / gScreenParams.xy;

    output.position = view.clipPosition;
    output.position.xy += deltaScreenPosition * view.clipPosition.w;
    output.color = color;
    output.localPosition = quadPosition;
    return output;
}