[ShaderGraph] Fix sprite previews for URP

Sets default material properties that are needed by sprite previews. This is a bit of a hotfix- it's probably better if the sprite target were to create these as hidden material properties so that these default values could be setup.

Packages/com.unity.shadergraph/Editor/Drawing/PreviewManager.cs

@@ -11,7 +11,6 @@
 using Object = UnityEngine.Object;
 using Unity.Profiling;
 
-
 namespace UnityEditor.ShaderGraph.Drawing
 {
     delegate void OnPrimaryMasterChanged();
@@ -518,6 +517,9 @@ bool TimedNodesShouldUpdate(EditorWindow editorWindow)
         }
 
         private static readonly ProfilerMarker RenderPreviewsMarker = new ProfilerMarker("RenderPreviews");
+        private static int k_spriteProps = Shader.PropertyToID("unity_SpriteProps");
+        private static int k_spriteColor = Shader.PropertyToID("unity_SpriteColor");
+        private static int k_rendererColor = Shader.PropertyToID("_RendererColor");
         public void RenderPreviews(EditorWindow editorWindow, bool requestShaders = true)
         {
             using (RenderPreviewsMarker.Auto())
@@ -673,6 +675,11 @@ public void RenderPreviews(EditorWindow editorWindow, bool requestShaders = true
                     previewTransform *= Matrix4x4.Scale(scale * Vector3.one * (Vector3.one).magnitude / mesh.bounds.size.magnitude);
                     previewTransform *= Matrix4x4.Translate(-mesh.bounds.center);
 
+                    //bugfix for some variables that need to be setup for URP Sprite material previews. Want a better isolated place to put them,
+                    //but I dont believe such a place exists and would be too costly to add.
+                    masterRenderData.shaderData.mat.SetVector(k_spriteProps, new Vector4(1, 1, -1, 0));
+                    masterRenderData.shaderData.mat.SetVector(k_spriteColor, new Vector4(1, 1, 1, 1));
+                    masterRenderData.shaderData.mat.SetVector(k_rendererColor, new Vector4(1, 1, 1, 1));
                     RenderPreview(masterRenderData, mesh, previewTransform, perMaterialPreviewProperties);
                 }