// Prism fullscreen texture blit shader.
//
// Draws a selected texture from the bindless array as a fullscreen quad that
// is letterboxed/pillarboxed to preserve aspect ratio (contain-fit). The NDC
// content rect is supplied via push constants so the texture is never
// stretched, squashed, or cropped.

struct BlitData {
	float4 rect;   // NDC fit rect: x0, y0, x1, y1
	uint   selected;
	uint   mode;   // 0 = sample texture, 1 = solid background
	uint   pad[2];
};

[[vk::push_constant]]
BlitData blit;

Sampler2D textures[];

struct VSOutput {
	float4 Pos : SV_POSITION;
	float2 UV;
};

[shader("vertex")]
VSOutput main(uint vertexIndex : SV_VertexID) {
	VSOutput output;
	float2 uv = float2(float(vertexIndex & 1), float((vertexIndex >> 1) & 1));
	output.UV = uv;
	float2 pos = lerp(blit.rect.xy, blit.rect.zw, uv);
	output.Pos = float4(pos, 0.0, 1.0);
	return output;
}

[shader("fragment")]
float4 main(VSOutput input) {
	if (blit.mode == 1) {
		return float4(0.18, 0.18, 0.18, 1.0);
	}
	return textures[NonUniformResourceIndex(blit.selected)].Sample(input.UV);
}