// Reference grid on the XZ plane. Uniforms live in a ConstantBuffer (UBO) so both
// backends drive it through the same RHI path (bind a uniform buffer at binding 0).
struct GridU
{
    float4x4 u_ViewProjection;
    float4x4 u_Transform;
    float    u_GridSize;
    float3   u_GridColor;
    float    u_GridAlpha;
    float3   u_CameraPos;
};
ConstantBuffer<GridU> gu;

struct VSInput  { float3 position : POSITION; };
struct VSOutput { float4 position : SV_Position; };

[shader("vertex")]
VSOutput vertexMain(VSInput input)
{
    VSOutput output;
    float3 scaledPosition = input.position * (gu.u_GridSize / 50.0);
    output.position = mul(gu.u_ViewProjection, mul(gu.u_Transform, float4(scaledPosition, 1.0)));
    return output;
}

[shader("fragment")]
float4 fragmentMain(VSOutput input) : SV_Target
{
    float dist       = length(gu.u_CameraPos);
    float fadeFactor = 1.0 - clamp(dist / 100.0, 0.0, 0.8);

    float3 color = gu.u_GridColor;
    float  alpha = gu.u_GridAlpha * fadeFactor;

    float gridFade = 1.0 - clamp(dist / 50.0, 0.0, 0.9);
    alpha *= gridFade;

    return float4(color, alpha);
}