make nodes more const friendly and prepare their functions for stateless work

Since the nodes won't be holding any rendering data themselves in this system,
we may as well enforce some level of non-write access by setting all the
functions to const. They were already const-friendly, they just weren't
labelled as such.

app/node/node.h

@@ -30,6 +30,7 @@
 #include "node/input.h"
 #include "node/inputarray.h"
 #include "node/output.h"
+#include "node/value.h"
 
 /**
  * @brief A single processing unit that can be connected with others to create intricate processing systems
@@ -59,7 +60,7 @@ public:
    * By default, the clone will NOT have the values and connections of the original node. The caller is responsible for
    * copying that data with functions like CopyInputs() as copies may be done for different reasons.
    */
-  virtual Node* copy() = 0;
+  virtual Node* copy() const = 0;
 
   /**
    * @brief Return the name of the node
@@ -67,7 +68,7 @@ public:
    * This is the node's name shown to the user. This must be overridden by subclasses, and preferably run through the
    * translator.
    */
-  virtual QString Name() = 0;
+  virtual QString Name() const = 0;
 
   /**
    * @brief Return the unique identifier of the node
@@ -76,7 +77,7 @@ public:
    * completely unique to this node, and preferably in bundle identifier format (e.g. "org.company.Name"). This string
    * should NOT be translated.
    */
-  virtual QString id() = 0;
+  virtual QString id() const = 0;
 
   /**
    * @brief Return the category this node is in (optional for subclassing, but recommended)
@@ -86,7 +87,7 @@ public:
    * interpreted as an empty string category. This value should be run through a translator as its largely user
    * oriented.
    */
-  virtual QString Category();
+  virtual QString Category() const;
 
   /**
    * @brief Return a description of this node's purpose (optional for subclassing, but recommended)
@@ -94,7 +95,7 @@ public:
    * A short (1-2 sentence) description of what this node should do to help the user understand its purpose. This should
    * be run through a translator.
    */
-  virtual QString Description();
+  virtual QString Description() const;
 
   /**
    * @brief Signals the Node that it won't be used for a while and can deallocate some memory
@@ -109,18 +110,18 @@ public:
   /**
    * @brief Return a list of NodeParams
    */
-  const QList<NodeParam*>& parameters();
+  const QList<NodeParam*>& parameters() const;
 
   /**
    * @brief Return the index of a parameter
    * @return Parameter index or -1 if this parameter is not part of this Node
    */
-  int IndexOfParameter(NodeParam* param);
+  int IndexOfParameter(NodeParam* param) const;
 
   /**
    * @brief Return a list of all Nodes that this Node's inputs are connected to (does not include this Node)
    */
-  QList<Node*> GetDependencies();
+  QList<Node*> GetDependencies() const;
 
   /**
    * @brief Returns a list of Nodes that this Node is dependent on, provided no other Nodes are dependent on them
@@ -128,47 +129,47 @@ public:
    *
    * Similar to GetDependencies(), but excludes any Nodes that are used outside the dependency graph of this Node.
    */
-  QList<Node*> GetExclusiveDependencies();
+  QList<Node*> GetExclusiveDependencies() const;
 
   /**
    * @brief Retrieve immediate dependencies (only nodes that are directly connected to the inputs of this one)
    */
-  QList<Node*> GetImmediateDependencies();
+  QList<Node*> GetImmediateDependencies() const;
 
   /**
    * @brief Generate OpenCL hardware accelerated code for this Node
    */
-  virtual QString Code(NodeOutput* output);
+  virtual QString Code(NodeOutput* output) const;
 
   /**
    * @brief Returns the parameter with the specified ID (or nullptr if it doesn't exist)
    */
-  NodeParam* GetParameterWithID(const QString& id);
+  NodeParam* GetParameterWithID(const QString& id) const;
 
   /**
    * @brief Returns whether this Node outputs data to the Node `n` in any way
    */
-  bool OutputsTo(Node* n);
+  bool OutputsTo(Node* n) const;
 
   /**
    * @brief Return whether this Node has input parameters
    */
-  bool HasInputs();
+  bool HasInputs() const;
 
   /**
    * @brief Return whether this Node has output parameters
    */
-  bool HasOutputs();
+  bool HasOutputs() const;
 
   /**
    * @brief Return whether this Node has input parameters and at least one of them is connected
    */
-  bool HasConnectedInputs();
+  bool HasConnectedInputs() const;
 
   /**
    * @brief Return whether this Node has output parameters and at least one of them is connected
    */
-  bool HasConnectedOutputs();
+  bool HasConnectedOutputs() const;
 
   /**
    * @brief Severs all input and output connections
@@ -197,7 +198,7 @@ public:
    */
   virtual void InvalidateCache(const rational& start_range, const rational& end_range, NodeInput* from = nullptr);
 
-  virtual TimeRange InputTimeAdjustment(NodeInput* input, const TimeRange& input_time);
+  virtual TimeRange InputTimeAdjustment(NodeInput* input, const TimeRange& input_time) const;
 
   /**
    * @brief User input lock prevents any user changes while a graph is being rendered
@@ -205,13 +206,6 @@ public:
   void LockUserInput();
   void UnlockUserInput();
 
-  /**
-   * @brief Processing lock prevents more than one thread trying to process a Node at once
-   */
-  void LockProcessing();
-  void UnlockProcessing();
-  bool IsProcessingLocked();
-
   /**
    * @brief Copies inputs from from Node to another including connections
    *
@@ -227,7 +221,7 @@ public:
   /**
    * @brief Return whether this Node can be deleted or not
    */
-  bool CanBeDeleted();
+  bool CanBeDeleted() const;
 
   /**
    * @brief Set whether this Node can be deleted in the UI or not
@@ -240,7 +234,7 @@ public:
    * You shouldn't ever need to override this since all derivatives of Block will automatically have this set to true.
    * It's just a more convenient way of checking than dynamic_casting.
    */
-  virtual bool IsBlock();
+  virtual bool IsBlock() const;
 
   /**
    * @brief Returns whether this Node is a "Track" type or not
@@ -248,7 +242,7 @@ public:
    * You shouldn't ever need to override this since all derivatives of Track will automatically have this set to true.
    * It's just a more convenient way of checking than dynamic_casting.
    */
-  virtual bool IsTrack();
+  virtual bool IsTrack() const;
 
   /**
    * @brief The main processing function
@@ -263,12 +257,12 @@ public:
    * corresponding output if it's connected to one. If your node doesn't directly deal with time, the default behavior
    * of the NodeParam objects will handle everything related to it automatically.
    */
-  virtual QVariant Value(NodeOutput* output);
+  virtual NodeValueTable Value(const NodeValueDatabase& value) const;
 
   /**
    * @brief Return whether a parameter with ID `id` has already been added to this Node
    */
-  bool HasParamWithID(const QString& id);
+  bool HasParamWithID(const QString& id) const;
 
 protected:
   /**
@@ -318,7 +312,7 @@ signals:
   void EdgeRemoved(NodeEdgePtr edge);
 
 private:
-  bool HasParamOfType(NodeParam::Type type, bool must_be_connected);
+  bool HasParamOfType(NodeParam::Type type, bool must_be_connected) const;
 
   void ConnectInput(NodeInput* input);
 
@@ -341,11 +335,6 @@ private:
    */
   QMutex user_input_lock_;
 
-  /**
-   * @brief Used for thread safety between multiple threads
-   */
-  QMutex processing_lock_;
-
   /**
    * @brief Internal variable for whether this Node can be deleted or not
    */