[D3D12] Immediate drawer pixel shader and root signature

src/xenia/ui/d3d12/shaders/immediate.ps.hlsl

@@ -0,0 +1,16 @@
+Texture2D<float4> immediate_texture : register(t0);
+SamplerState immediate_sampler : register(s0);
+bool restrict_texture_samples : register(b0);
+
+struct ps_input {
+  float2 uv : TEXCOORD0;
+  float4 color : TEXCOORD1;
+};
+
+float4 main(ps_input input) : SV_Target {
+  float4 output = input.color;
+  if (!restrict_texture_samples || input.uv.x <= 1.0) {
+    output *= immediate_texture.Sample(immediate_sampler, input.uv);
+  }
+  return output;
+}

src/xenia/ui/d3d12/shaders/immediate.vs.hlsl

@@ -1,4 +1,4 @@
-float2 scale : register(b0);
+float2 viewport_inv_size : register(b0);
 
 struct vs_input {
   float2 pos : POSITION;
@@ -14,7 +14,7 @@ struct vs_output {
 
 vs_output main(vs_input input) {
   vs_output output;
-  output.pos = float4(scale * input.pos, 0.0, 1.0);
+  output.pos = float4(viewport_inv_size * input.pos, 0.0, 1.0);
   output.uv = input.uv;
   output.color = input.color;
   return output;