uniform float4x4 ViewProj;
uniform texture2d image;
uniform texture2d background;

sampler_state textureSampler{
    Filter = Linear;
    AddressU = Clamp;
    AddressV = Clamp;
    MinLOD = 0;
    MaxLOD = 0;
};

struct VertData {
    float4 pos : POSITION;
    float2 uv : TEXCOORD0;
};

VertData mainTransform(VertData v_in)
{
    v_in.pos = mul(float4(v_in.pos.xyz, 1.0), ViewProj);
    return v_in;
}

float4 mainImage(VertData v_in) : TARGET
{
    float4 img_col = image.Sample(textureSampler, v_in.uv);
    float4 background_col = background.Sample(textureSampler, v_in.uv);
    float a = img_col.a;
    float3 color = img_col.rgb * a + background_col.rgb * (1.0 - a);
    return float4(color.rgb, a);
}

technique Draw
{
    pass
    {
        vertex_shader = mainTransform(v_in);
        pixel_shader = mainImage(v_in);
    }
}