Add collapse button on master preview

com.unity.shadergraph/Editor/Drawing/Inspector/MasterPreviewView.cs

         IMasterNode m_MasterNode;
         Mesh m_PreviousMesh;
 
+        bool m_Expanded = true;
+
+        public bool expanded
+        {
+            get { return m_Expanded;}
+        }
+
+        Vector2 m_ExpandedPreviewSize;
+
+        VisualElement m_CollapsePreviewContainer;
+        VisualElement m_CollapsePreviewButton;
+        ResizeBorderFrame m_PreviewResizeBorderFrame;
+
+        public ResizeBorderFrame previewResizeBorderFrame
+        {
+            get { return m_PreviewResizeBorderFrame; }
+        }
+
         VisualElement m_Preview;
 
         public VisualElement preview
             var topContainer = new VisualElement() { name = "top" };
             {
                 var title = new Label(assetName.Split('/').Last()) { name = "title" };
+
+                // Add preview collapse button on top of preview
+                m_CollapsePreviewContainer = new VisualElement { name = "collapse-container" };
+                m_CollapsePreviewContainer.AddToClassList("collapse-container");
+                m_CollapsePreviewButton = new VisualElement { name = "icon" };
+                m_CollapsePreviewButton.AddToClassList("icon");
+                m_CollapsePreviewContainer.Add(m_CollapsePreviewButton);
+                m_CollapsePreviewContainer.AddManipulator(new Clickable(() =>
+                {
+                    m_Graph.owner.RegisterCompleteObjectUndo("Collapse Preview");
+                    m_Expanded ^= true;
+                    UpdateExpandedButtonState();
+                    UpdatePreviewVisibility();
+                }));
+
+                topContainer.Add(m_CollapsePreviewContainer);
             }
             Add(topContainer);
 
             }
             m_PreviewRenderHandle.onPreviewChanged += OnPreviewChanged;
             Add(preview);
+
+            m_PreviewResizeBorderFrame = new ResizeBorderFrame(previewTextureView, this) { name = "resizeBorderFrame" };
+            m_PreviewResizeBorderFrame.stayWithinParentBounds = true;
+            m_PreviewResizeBorderFrame.maintainAspectRatio = true;
+            Add(m_PreviewResizeBorderFrame);
+
+            m_ExpandedPreviewSize = new Vector2(256f, 256f);
+        }
+
+        void UpdateExpandedButtonState()
+        {
+            m_CollapsePreviewButton.RemoveFromClassList(!m_Expanded ? "expanded" : "collapsed");
+            m_CollapsePreviewButton.AddToClassList(!m_Expanded ? "collapsed" : "expanded");
+        }
+
+        void UpdatePreviewVisibility()
+        {
+            if (m_Expanded)
+            {
+                RemoveFromClassList("collapsed");
+                AddToClassList("expanded");
+                m_PreviewResizeBorderFrame.visible = true;
+                previewTextureView.style.width = StyleValue<float>.Create(m_ExpandedPreviewSize.x);
+                previewTextureView.style.height = StyleValue<float>.Create(m_ExpandedPreviewSize.y);
+            }
+            else
+            {
+                m_ExpandedPreviewSize = previewTextureView.layout.size;
+                m_PreviewResizeBorderFrame.visible = false;
+                previewTextureView.style.width = StyleValue<float>.Create(0f);
+                previewTextureView.style.height = StyleValue<float>.Create(0f);
+                RemoveFromClassList("expanded");
+                AddToClassList("collapsed");
+            }
         }
 
         Image CreatePreview(Texture texture)
 
         public void RefreshRenderTextureSize()
         {
+            if (!expanded)
+                return;
+
             var currentWidth = m_PreviewRenderHandle.texture != null ? m_PreviewRenderHandle.texture.width : -1;
             var currentHeight = m_PreviewRenderHandle.texture != null ? m_PreviewRenderHandle.texture.height : -1;
 

com.unity.shadergraph/Editor/Drawing/Views/GraphEditorView.cs

                 m_MasterPreviewView.AddManipulator(masterPreviewViewDraggable);
                 m_GraphView.Add(m_MasterPreviewView);
 
-                ResizeBorderFrame masterPreviewResizeBorderFrame = new ResizeBorderFrame(m_MasterPreviewView.previewTextureView, m_MasterPreviewView) { name = "resizeBorderFrame" };
-                masterPreviewResizeBorderFrame.stayWithinParentBounds = true;
-                masterPreviewResizeBorderFrame.maintainAspectRatio = true;
-                masterPreviewResizeBorderFrame.OnResizeFinished += UpdateSerializedWindowLayout;
-                m_MasterPreviewView.Add(masterPreviewResizeBorderFrame);
-
-                masterPreviewResizeBorderFrame.OnResizeFinished += UpdateSerializedWindowLayout;
+                m_MasterPreviewView.previewResizeBorderFrame.OnResizeFinished += UpdateSerializedWindowLayout;
 
                 m_GraphView.graphViewChanged = GraphViewChanged;
 
 
             m_FloatingWindowsLayout.previewLayout.CalculateDockingCornerAndOffset(m_MasterPreviewView.layout, layout);
             m_FloatingWindowsLayout.blackboardLayout.CalculateDockingCornerAndOffset(m_BlackboardProvider.blackboard.layout, layout);
-            m_FloatingWindowsLayout.masterPreviewSize = m_MasterPreviewView.previewTextureView.layout.size;
+
+            if (m_MasterPreviewView.expanded)
+            {
+                m_FloatingWindowsLayout.masterPreviewSize = m_MasterPreviewView.previewTextureView.layout.size;
+            }
 
             string serializedWindowLayout = JsonUtility.ToJson(m_FloatingWindowsLayout);
             EditorUserSettings.SetConfigValue(k_FloatingWindowsLayoutKey, serializedWindowLayout);

com.unity.shadergraph/Editor/Resources/Styles/MasterPreviewView.uss

 }
 
 MasterPreviewView > #top {
+    flex-direction: row;
+    justify-content: space-between;
     background-color: rgb(64, 64, 64);
     padding-top: 8;
     padding-bottom: 8;
     padding-right: 2;
 }
 
+MasterPreviewView > #top > #collapse-container {
+    align-self : center;
+    width : 12;
+}
+
+MasterPreviewView > #top > #collapse-container > #icon{
+    align-self: center;
+    background-image : resource("GraphView/Nodes/NodeChevronDown");
+    width: 12;
+    height: 12;
+    margin-right: 10;
+    margin-left: 10;
+}
+
+MasterPreviewView > #top > #collapse-container > #icon.collapsed {
+    align-self: center;
+    background-image : resource("GraphView/Nodes/NodeChevronLeft");
+    width: 12;
+    height: 12;
+}
+
+MasterPreviewView > #top > #collapse-container > #icon.expanded {
+    align-self: center;
+    background-image : resource("GraphView/Nodes/NodeChevronDown");
+    width: 12;
+    height: 12;
+}
+
 MasterPreviewView > #middle {
     flex-grow: 1;
     border-width: 10;
     width: 200;
     height: 200;
 }
+
+MasterPreviewView.collapsed{
+    background-color: rgb(206, 53, 185);
+}
+
+MasterPreviewView.expanded{
+    background-color: rgb(206, 53, 185);
+}