Hypershade-style pin display modes for material graph nodes

Each node gets an All/Conn toggle: connected-only mode hides
unconnected pins behind collapsed connector nubs on the title row;
dragging a link onto (or from) a nub opens a menu to pick which hidden
pin to wire, and the pin appears once connected. The toggle is drawn
and hit-tested geometrically, and its tooltip is deferred to after
NE::End() so it lands at the cursor. A new Preferences > Material
checkbox opts into persisting the per-node mode as USD customData
(uiShowAllPins); otherwise it stays session-only.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/ui/MaterialEditorPanel.h

@@ -54,6 +54,12 @@ public:
     }
     void SetColumnWidths(float browserWidth, float previewWidth);
 
+    /// Whether toggling a node's pin display mode / revealing a hidden pin
+    /// authors USD customData (persisted) or stays session-only. Pushed in by
+    /// Application from AppPreferences, live-updated when the user flips the
+    /// checkbox in Preferences -> Material.
+    void SetKeepGraphNodeViewSettingsInUsd(bool value) { m_keepGraphNodeViewSettingsInUsd = value; }
+
     void Render();
 
 private:
@@ -63,6 +69,12 @@ private:
         std::string  name;
         bool         isOutput = false;
         pxr::SdfValueTypeName typeName;
+        /// True for the collapsed "more pins" connector nub rendered on a
+        /// node's title row when it's hiding unconnected pins (Hypershade
+        /// style) — name/typeName are unset. Connecting to/from it opens
+        /// RenderPinPickMenu() to choose which actual pin to wire, instead of
+        /// creating the connection immediately. See HandleCreateAndDelete().
+        bool         isMeta = false;
     };
     /// Resolved endpoint of a rendered link, keyed by its ax::NodeEditor LinkId.
     struct LinkInfo {
@@ -70,6 +82,24 @@ private:
         std::string  destInput;
     };
 
+    /// Hypershade-style per-node pin display state. Always the render-time
+    /// source of truth (never resync-clobbered); optionally mirrored into USD
+    /// customData when m_keepGraphNodeViewSettingsInUsd is set. See
+    /// GetPinDisplayOverride()/IsPinVisible().
+    struct PinDisplayOverride {
+        bool showAllPins = true;
+    };
+    /// A connection dragged onto/from a collapsed meta pin, awaiting the user
+    /// picking which actual pin on nodePath/isOutput to wire up. otherPin is
+    /// the already-resolved endpoint on the far side of the link (itself meta
+    /// if the user dragged directly between two collapsed nubs, in which case
+    /// picking chains into a second RenderPinPickMenu() for that side).
+    struct PendingPinPick {
+        pxr::SdfPath nodePath;
+        bool         isOutput = false;
+        PinInfo      otherPin;
+    };
+
     void RenderToolbar();
     /// Property editor for the node selected in the graph, shown below the
     /// shader-ball preview. Values apply live while a widget is being
@@ -122,6 +152,35 @@ private:
     void PersistNodePosition(ax::NodeEditor::NodeId nodeId);
     bool IsPinLinked(const pxr::SdfPath& nodePath, const std::string& pinName, bool isOutput) const;
 
+    /// Seeds m_pinDisplayOverrides for any node path not already present
+    /// (i.e. not touched yet this session) from the just-synced m_graph's
+    /// showAllPins (customData-backed). Never overwrites an existing entry,
+    /// so in-session toggles survive resyncs.
+    void SeedPinDisplayOverrides();
+    /// Creates the entry (defaulted to "show all") on first access.
+    PinDisplayOverride& GetPinDisplayOverride(const pxr::SdfPath& nodePath);
+    /// True if pin should be drawn this frame: node is in "show all" mode, or
+    /// the pin is linked (linked pins are never hidden — Link() unconditionally
+    /// references pin IDs that must have been drawn). A hidden pin becomes
+    /// visible the moment it's connected, via RenderPinPickMenu().
+    bool IsPinVisible(const ShaderGraphNode& node, const std::string& pinName, bool isOutput) const;
+    /// Flips a node between "show all" and "show connected only".
+    void TogglePinDisplayMode(const pxr::SdfPath& nodePath);
+    /// Authors the node's current PinDisplayOverride into USD customData via
+    /// an undoable command, mirroring PersistNodePosition. No-op unless
+    /// m_keepGraphNodeViewSettingsInUsd is set.
+    void PersistPinDisplayState(const pxr::SdfPath& nodePath);
+    /// Renders the deferred "choose pin" popup for m_pendingPinPick (Maya
+    /// Hypershade style): a connection was dragged onto/from a collapsed meta
+    /// pin, and the user now picks which actual attribute it wires to. Must
+    /// be called from within the NE::Suspend()/Resume() block, like the
+    /// other popups.
+    void RenderPinPickMenu();
+    /// Finishes a pick: creates the real connection to/from chosen, unless
+    /// the far side of the pending pick was itself a meta pin, in which case
+    /// this chains into a second pick for that side instead.
+    void CompletePinPick(const PinInfo& chosen);
+
     static bool SaveNodeSettingsCallback(ax::NodeEditor::NodeId nodeId,
                                          const char* data, size_t size,
                                          ax::NodeEditor::SaveReasonFlags reason,
@@ -170,6 +229,18 @@ private:
     bool    m_openLinkDragMenu = false;
     PinInfo m_linkDragSourcePin;
 
+    /// Hypershade-style pin display state, keyed by node path string. Always
+    /// the render-time source of truth; see PinDisplayOverride.
+    std::unordered_map<std::string, PinDisplayOverride> m_pinDisplayOverrides;
+    /// Whether node toggles author USD customData (see
+    /// SetKeepGraphNodeViewSettingsInUsd).
+    bool m_keepGraphNodeViewSettingsInUsd = false;
+    /// Deferred "choose pin" popup request: set from HandleCreateAndDelete()
+    /// when a link is dropped on/dragged from a collapsed meta pin, actually
+    /// opened after NE::Suspend(), like m_openLinkDragMenu.
+    bool            m_openPinPickMenu = false;
+    PendingPinPick  m_pendingPinPick;
+
     /// Column widths of the browser (left) and preview (right) sections,
     /// user-adjustable via the splitters between them and the canvas.
     float m_browserWidth = 220.0f;