began port of previous renderer iteration to new iteration

This will essentially be a full rewrite, but very incrementally to save time
and energy.

app/render/backend/renderbackend.cpp

@@ -1,6 +1,7 @@
 #include "renderbackend.h"
 
-RenderBackend::RenderBackend() :
+RenderBackend::RenderBackend(QObject *parent) :
+  QObject(parent),
   viewer_node_(nullptr)
 {
 
@@ -10,7 +11,7 @@ RenderBackend::~RenderBackend()
 {
 }
 
-const QString &RenderBackend::GetError()
+const QString &RenderBackend::GetError() const
 {
   return error_;
 }
@@ -19,14 +20,18 @@ void RenderBackend::SetViewerNode(ViewerOutput *viewer_node)
 {
   if (viewer_node_ != nullptr) {
     disconnect(viewer_node_, SIGNAL(TextureChangedBetween(const rational&, const rational&)), this, SLOT(Compile()));
+    disconnect(viewer_node_, SIGNAL(TextureChangedBetween(const rational&, const rational&)), this, SLOT(InvalidateCache(const rational&, const rational&)));
   }
 
   viewer_node_ = viewer_node;
 
   if (viewer_node_ != nullptr) {
     connect(viewer_node_, SIGNAL(TextureChangedBetween(const rational&, const rational&)), this, SLOT(Compile()));
+    connect(viewer_node_, SIGNAL(TextureChangedBetween(const rational&, const rational&)), this, SLOT(InvalidateCache(const rational&, const rational&)));
   }
 
+  ViewerNodeChangedEvent(viewer_node_);
+
   Decompile();
 }
 
@@ -35,6 +40,11 @@ void RenderBackend::SetError(const QString &error)
   error_ = error;
 }
 
+void RenderBackend::ViewerNodeChangedEvent(ViewerOutput *node)
+{
+  Q_UNUSED(node)
+}
+
 ViewerOutput *RenderBackend::viewer_node() const
 {
   return viewer_node_;