Intial somewhat working version

shaders/black_white/shader.hlsl

@@ -0,0 +1,53 @@
+struct VSOut
+{
+    float4 position : SV_Position;
+    float2 uv : TEXCOORD0;
+};
+
+cbuffer FrameConstants : register(b0)
+{
+    float width;
+    float height;
+    float frameIndex;
+    float frameReserved;
+};
+
+cbuffer ShaderParameters : register(b1)
+{
+    float amount;
+    float3 parameterPadding;
+};
+
+Texture2D<float4> inputFrame : register(t0);
+SamplerState linearClampSampler : register(s0);
+
+VSOut fullscreen_vs(uint vertexId : SV_VertexID)
+{
+    float2 positions[3] =
+    {
+        float2(-1.0, -1.0),
+        float2(-1.0,  3.0),
+        float2( 3.0, -1.0)
+    };
+
+    float2 uvs[3] =
+    {
+        float2(0.0, 1.0),
+        float2(0.0, -1.0),
+        float2(2.0, 1.0)
+    };
+
+    VSOut output;
+    output.position = float4(positions[vertexId], 0.0, 1.0);
+    output.uv = uvs[vertexId];
+    return output;
+}
+
+float4 main(VSOut input) : SV_Target
+{
+    float4 color = inputFrame.Sample(linearClampSampler, input.uv);
+    float luminance = dot(color.rgb, float3(0.2126, 0.7152, 0.0722));
+    float3 gray = luminance.xxx;
+    color.rgb = lerp(color.rgb, gray, saturate(amount));
+    return color;
+}

shaders/black_white/shader.json

@@ -0,0 +1,17 @@
+{
+  "id": "builtin.black_white",
+  "name": "Black & White",
+  "version": 1,
+  "entry": "main",
+  "type": "fullscreen_pixel",
+  "parameters": [
+    {
+      "id": "amount",
+      "label": "Amount",
+      "type": "float",
+      "default": 1.0,
+      "min": 0.0,
+      "max": 1.0
+    }
+  ]
+}