Fix Screen Position and Reflection Probe nodes

- Requires reorder of preview shader includes
- Requires adding EntityLighting.hlsl to preview shader includes (For DecodeHDREnvironment)
- Requires addeing unity_SpecCube0 (texture, sampler and instruction) to ShaderVariables.hlsl (for Preview shader)
- Added "legacy" ComputeScreenPos function

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Data/Nodes/Input/Geometry/ScreenPositionNode.cs

             switch (m_ScreenSpaceType)
             {
                 case ScreenSpaceType.Raw:
-                    visitor.AddShaderChunk(string.Format("{0}4 {1} = In.{2};", precision, GetVariableNameForSlot(kOutputSlotId),
+                    visitor.AddShaderChunk(string.Format("{0}4 {1} = IN.{2};", precision, GetVariableNameForSlot(kOutputSlotId),
-                        string.Format("float4((In.{0}.xy / In.{0}.w) * 2 - 1, 0, 0)", ShaderGeneratorNames.ScreenPosition)), true);
+                        string.Format("float4((IN.{0}.xy / IN.{0}.w) * 2 - 1, 0, 0)", ShaderGeneratorNames.ScreenPosition)), true);
-                        string.Format("float4((In.{0}.xy / In.{0}.w) * 2 - 1, 0, 0)", ShaderGeneratorNames.ScreenPosition)), true);
+                        string.Format("float4((IN.{0}.xy / IN.{0}.w) * 2 - 1, 0, 0)", ShaderGeneratorNames.ScreenPosition)), true);
-                        string.Format("float4(In.{0}.x * _ScreenParams.x / _ScreenParams.y, In.{0}.y, 0, 0)", ShaderGeneratorNames.ScreenPosition)), true);
+                        string.Format("float4(IN.{0}.x * _ScreenParams.x / _ScreenParams.y, IN.{0}.y, 0, 0)", ShaderGeneratorNames.ScreenPosition)), true);
-                        string.Format("float4(In.{0}.xy / In.{0}.w, 0, 0)", ShaderGeneratorNames.ScreenPosition)), true);
+                        string.Format("float4(IN.{0}.xy / IN.{0}.w, 0, 0)", ShaderGeneratorNames.ScreenPosition)), true);
                     break;
             }
         }

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Data/Nodes/Input/Scene/ReflectionProbeNode.cs

                 @"
 {
     {precision}3 reflectVec = reflect(-ViewDir, Normal);
-    Out = DecodeHDR(UNITY_SAMPLE_TEXCUBE_LOD(unity_SpecCube0, reflectVec, LOD), unity_SpecCube0_HDR);
+    Out = DecodeHDREnvironment(SAMPLE_TEXTURECUBE_LOD(unity_SpecCube0, samplerunity_SpecCube0, reflectVec, LOD), unity_SpecCube0_HDR);
 }
 ";
         }

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Data/Util/GraphUtil.cs

                 finalBuilder.AppendLine(@"#include ""CoreRP/ShaderLibrary/Common.hlsl""");
                 finalBuilder.AppendLine(@"#include ""CoreRP/ShaderLibrary/Packing.hlsl""");
                 finalBuilder.AppendLine(@"#include ""CoreRP/ShaderLibrary/Color.hlsl""");
-                finalBuilder.AppendLine(@"#include ""ShaderGraphLibrary/Functions.hlsl""");
+                finalBuilder.AppendLine(@"#include ""CoreRP/ShaderLibrary/EntityLighting.hlsl""");
-
+                finalBuilder.AppendLine(@"#include ""ShaderGraphLibrary/Functions.hlsl""");
 
                 finalBuilder.AppendLines(shaderProperties.GetPropertiesDeclaration(0));
                 finalBuilder.AppendLines(surfaceInputs.GetShaderString(0));

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Data/Util/ShaderGenerator.cs

             if (combinedRequierments.requiresScreenPosition)
             {
                 interpolators.AddShaderChunk(string.Format("float4 {0} : TEXCOORD{1};", ShaderGeneratorNames.ScreenPosition, interpolatorIndex), false);
-                vertexShader.AddShaderChunk(string.Format("o.{0} = ComputeScreenPos(UnityObjectToClipPos(v.vertex));", ShaderGeneratorNames.ScreenPosition), false);
+                vertexShader.AddShaderChunk(string.Format("o.{0} = ComputeScreenPos(mul(GetWorldToHClipMatrix(), mul(GetObjectToWorldMatrix(), v.vertex)));", ShaderGeneratorNames.ScreenPosition), false);
                 pixelShader.AddShaderChunk(string.Format("float4 {0} = IN.{0};", ShaderGeneratorNames.ScreenPosition), false);
                 interpolatorIndex++;
             }

MaterialGraphProject/Assets/UnityShaderEditor/ShaderGraphLibrary/Functions.hlsl

     #endif
 }
 
+float4 ComputeScreenPos (float4 pos) 
+{
+  float4 o = pos * 0.5f;
+  o.xy = float2(o.x, o.y*_ProjectionParams.x) + o.w;
+  o.zw = pos.zw;
+  return o;
+}
+
 #endif // UNITY_SHADER_GRAPH_INCLUDED

MaterialGraphProject/Assets/UnityShaderEditor/ShaderGraphLibrary/ShaderVariables.hlsl

 
     // This contain occlusion factor from 0 to 1 for dynamic objects (no SH here)
     float4 unity_ProbesOcclusion;
-
+    
+    // HDR environment map decode instructions
+    half4 unity_SpecCube0_HDR;
 CBUFFER_END
 
 #if defined(USING_STEREO_MATRICES)
 SAMPLER(samplerunity_DynamicLightmap);
 
 TEXTURE2D(unity_DynamicDirectionality);
+
+// Default reflection probe
+TEXTURECUBE(unity_SpecCube0);
+SAMPLER(samplerunity_SpecCube0);
 
 // We can have shadowMask only if we have lightmap, so no sampler
 TEXTURE2D(unity_ShadowMask);