[Backport 6000.4] Fix gamma issue of Sample Element Texture node for Editor Window when using custom shaders.

Author: ncerone-unity

Packages/com.unity.shadergraph/Editor/Data/Nodes/UI/SampleElementTextureNode.cs

@@ -99,6 +99,13 @@ public void GenerateNodeCode(ShaderStringBuilder sb, GenerationMode generationMo
                     GetVariableNameForSlot(Color1SlotId),
                     GetVariableNameForSlot(Color2SlotId),
                     GetVariableNameForSlot(Color3SlotId));
+
+                sb.AppendLine("#if _UIE_FORCE_GAMMA");
+                sb.AppendLine("{0}.rgb = uie_linear_to_gamma({1}.rgb);", GetVariableNameForSlot(Color0SlotId), GetVariableNameForSlot(Color0SlotId));
+                sb.AppendLine("{0}.rgb = uie_linear_to_gamma({1}.rgb);", GetVariableNameForSlot(Color1SlotId), GetVariableNameForSlot(Color1SlotId));
+                sb.AppendLine("{0}.rgb = uie_linear_to_gamma({1}.rgb);", GetVariableNameForSlot(Color2SlotId), GetVariableNameForSlot(Color2SlotId));
+                sb.AppendLine("{0}.rgb = uie_linear_to_gamma({1}.rgb);", GetVariableNameForSlot(Color3SlotId), GetVariableNameForSlot(Color3SlotId));
+                sb.AppendLine("#endif");
             }
         }