// 2D image blit for the Direct3D backends (the D3D port of scene.vert/scene.frag).
//
// The scene image is drawn as a single fullscreen triangle sampling the
// software-rendered `ra3::render::image`. The constant buffer carries the
// destination rectangle in window-normalized coordinates (y down), so the map
// is letterboxed rather than stretched. D3D clip space has +Y up, so the vertex
// position flips Y relative to the Vulkan shader (which relies on Vulkan's
// +Y-down clip space); the sampled UVs and the image's top-left origin are
// unchanged.

cbuffer RectCB : register(b0) {
    float4 rect; // xy = top-left (0..1), zw = size (0..1)
};

Texture2D scene_tex : register(t0);
SamplerState scene_smp : register(s0);

struct VSOut {
    float4 pos : SV_Position;
    float2 uv : TEXCOORD0;
};

VSOut VSMain(uint vertex_id : SV_VertexID) {
    float2 p = float2((vertex_id << 1) & 2, vertex_id & 2);
    VSOut o;
    o.uv = (p - rect.xy) / rect.zw;
    o.pos = float4(p.x * 2.0 - 1.0, 1.0 - p.y * 2.0, 0.0, 1.0);
    return o;
}

float4 PSMain(VSOut input) : SV_Target {
    if (input.uv.x < 0.0 || input.uv.x > 1.0 || input.uv.y < 0.0 || input.uv.y > 1.0) discard;
    return scene_tex.Sample(scene_smp, input.uv);
}