Formalize builtin shader resource contracts

engine/assets/builtin/shaders/depth-only.shader

@@ -0,0 +1,73 @@
+Shader "Builtin Depth Only"
+{
+    Properties
+    {
+        _BaseColor ("Base Color", Color) = (1,1,1,1) [Semantic(BaseColor)]
+        _Cutoff ("Alpha Cutoff", Range) = 0.5 [Semantic(AlphaCutoff)]
+        _MainTex ("Base Map", 2D) = "white" [Semantic(BaseColorTexture)]
+    }
+    HLSLINCLUDE
+    cbuffer PerObjectConstants
+    {
+        float4x4 gProjectionMatrix;
+        float4x4 gViewMatrix;
+        float4x4 gModelMatrix;
+    };
+
+    cbuffer MaterialConstants
+    {
+        float4 gBaseColorFactor;
+        float4 gAlphaCutoffParams;
+    };
+
+    Texture2D BaseColorTexture;
+    SamplerState LinearClampSampler;
+
+    struct VSInput
+    {
+        float3 position : POSITION;
+        float3 normal : NORMAL;
+        float2 texcoord : TEXCOORD0;
+    };
+
+    struct PSInput
+    {
+        float4 position : SV_POSITION;
+        float2 texcoord : TEXCOORD0;
+    };
+
+    PSInput MainVS(VSInput input)
+    {
+        PSInput output;
+        const float4 positionWS = mul(gModelMatrix, float4(input.position, 1.0f));
+        const float4 positionVS = mul(gViewMatrix, positionWS);
+        output.position = mul(gProjectionMatrix, positionVS);
+        output.texcoord = input.texcoord;
+        return output;
+    }
+
+    float MainPS(PSInput input) : SV_Depth
+    {
+    #ifdef XC_ALPHA_TEST
+        const float4 baseColor =
+            BaseColorTexture.Sample(LinearClampSampler, input.texcoord) * gBaseColorFactor;
+        clip(baseColor.a - gAlphaCutoffParams.x);
+    #endif
+        return input.position.z;
+    }
+    ENDHLSL
+    SubShader
+    {
+        Pass
+        {
+            Name "DepthOnly"
+            Tags { "LightMode" = "DepthOnly" }
+            HLSLPROGRAM
+            #pragma target 4.5
+            #pragma vertex MainVS
+            #pragma fragment MainPS
+            #pragma shader_feature_local _ XC_ALPHA_TEST
+            ENDHLSL
+        }
+    }
+}