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/input/media/audio/audio.cpp

@@ -6,27 +6,27 @@ AudioInput::AudioInput()
   AddParameter(samples_output_);
 }
 
-Node *AudioInput::copy()
+Node *AudioInput::copy() const
 {
   return new AudioInput();
 }
 
-QString AudioInput::Name()
+QString AudioInput::Name() const
 {
   return tr("Audio Input");
 }
 
-QString AudioInput::id()
+QString AudioInput::id() const
 {
   return "org.olivevideoeditor.Olive.audioinput";
 }
 
-QString AudioInput::Category()
+QString AudioInput::Category() const
 {
   return tr("Input");
 }
 
-QString AudioInput::Description()
+QString AudioInput::Description() const
 {
   return tr("Import an audio footage stream.");
 }
@@ -36,12 +36,7 @@ NodeOutput *AudioInput::samples_output()
   return samples_output_;
 }
 
-QVariant AudioInput::Value(NodeOutput *output)
+NodeValueTable AudioInput::Value(const NodeValueDatabase &value) const
 {
-  if (output == samples_output_) {
-    // Simple passthrough from footage input
-    return footage_input_->value();
-  }
-
-  return MediaInput::Value(output);
+  return value[footage_input_];
 }

app/node/input/media/audio/audio.h

@@ -8,17 +8,17 @@ class AudioInput : public MediaInput
 public:
   AudioInput();
 
-  virtual Node* copy() override;
+  virtual Node* copy() const override;
 
-  virtual QString Name() override;
-  virtual QString id() override;
-  virtual QString Category() override;
-  virtual QString Description() override;
+  virtual QString Name() const override;
+  virtual QString id() const override;
+  virtual QString Category() const override;
+  virtual QString Description() const override;
 
   NodeOutput* samples_output();
 
 protected:
-  virtual QVariant Value(NodeOutput* output) override;
+  virtual NodeValueTable Value(const NodeValueDatabase& value) const override;
 
 private:
   NodeOutput* samples_output_;

app/node/input/media/video/video.cpp

@@ -18,27 +18,27 @@ VideoInput::VideoInput()
   AddParameter(texture_output_);
 }
 
-Node *VideoInput::copy()
+Node *VideoInput::copy() const
 {
   return new VideoInput();
 }
 
-QString VideoInput::Name()
+QString VideoInput::Name() const
 {
   return tr("Video Input");
 }
 
-QString VideoInput::id()
+QString VideoInput::id() const
 {
   return "org.olivevideoeditor.Olive.videoinput";
 }
 
-QString VideoInput::Category()
+QString VideoInput::Category() const
 {
   return tr("Input");
 }
 
-QString VideoInput::Description()
+QString VideoInput::Description() const
 {
   return tr("Import a video footage stream.");
 }
@@ -48,17 +48,17 @@ void VideoInput::Release()
   MediaInput::Release();
 }
 
-NodeInput *VideoInput::matrix_input()
+NodeInput *VideoInput::matrix_input() const
 {
   return matrix_input_;
 }
 
-NodeOutput *VideoInput::texture_output()
+NodeOutput *VideoInput::texture_output() const
 {
   return texture_output_;
 }
 
-QString VideoInput::Code(NodeOutput *output)
+QString VideoInput::Code(NodeOutput *output) const
 {
   if (output == texture_output()) {
     return "#version 110\n"

app/node/input/media/video/video.h

@@ -11,20 +11,20 @@ class VideoInput : public MediaInput
 public:
   VideoInput();
 
-  virtual Node* copy() override;
+  virtual Node* copy() const override;
 
-  virtual QString Name() override;
-  virtual QString id() override;
-  virtual QString Category() override;
-  virtual QString Description() override;
+  virtual QString Name() const override;
+  virtual QString id() const override;
+  virtual QString Category() const override;
+  virtual QString Description() const override;
 
   virtual void Release() override;
 
-  NodeInput* matrix_input();
+  NodeInput* matrix_input() const;
 
-  NodeOutput* texture_output();
+  NodeOutput* texture_output() const;
 
-  virtual QString Code(NodeOutput* output) override;
+  virtual QString Code(NodeOutput* output) const override;
 
   //virtual void Hash(QCryptographicHash *hash, NodeOutput* from, const rational &time) override;