Trigger background processing update when switching to a preview tab.

Implements "Go Direct to the preview screen after slicing #152"

src/libslic3r/Print.hpp

@@ -297,7 +297,10 @@ public:
 
     // methods for handling state
     bool                is_step_done(PrintStep step) const { return Inherited::is_step_done(step); }
+    // Returns true if an object step is done on all objects and there's at least one object.    
     bool                is_step_done(PrintObjectStep step) const;
+    // Returns true if the last step was finished with success.
+    bool                finished() const override { return this->is_step_done(psGCodeExport); }
 
     bool                has_infinite_skirt() const;
     bool                has_skirt() const;

src/libslic3r/PrintBase.hpp

@@ -285,6 +285,8 @@ public:
 	void                       cancel_internal() { m_cancel_status = CANCELED_INTERNAL; }
     // Cancel the running computation. Stop execution of all the background threads.
 	void                       restart() { m_cancel_status = NOT_CANCELED; }
+    // Returns true if the last step was finished with success.
+    virtual bool               finished() const = 0;
 
     const PlaceholderParser&   placeholder_parser() const { return m_placeholder_parser; }
     PlaceholderParser&         placeholder_parser() { return m_placeholder_parser; }

src/libslic3r/SLAPrint.cpp

@@ -936,6 +936,18 @@ bool SLAPrint::invalidate_state_by_config_options(const std::vector<t_config_opt
     return invalidated;
 }
 
+// Returns true if an object step is done on all objects and there's at least one object.
+bool SLAPrint::is_step_done(SLAPrintObjectStep step) const
+{
+    if (m_objects.empty())
+        return false;
+    tbb::mutex::scoped_lock lock(this->state_mutex());
+    for (const SLAPrintObject *object : m_objects)
+        if (! object->m_state.is_done_unguarded(step))
+            return false;
+    return true;
+}
+
 SLAPrintObject::SLAPrintObject(SLAPrint *print, ModelObject *model_object):
     Inherited(print, model_object),
     m_stepmask(slaposCount, true),

src/libslic3r/SLAPrint.hpp

@@ -185,6 +185,9 @@ public:
     bool                empty() const override { return m_objects.empty(); }
     ApplyStatus         apply(const Model &model, const DynamicPrintConfig &config) override;
     void                process() override;
+    bool                is_step_done(SLAPrintObjectStep step) const;
+    // Returns true if the last step was finished with success.
+    bool                finished() const override { return this->is_step_done(slaposIndexSlices); }
 
     template<class Fmt> void export_raster(const std::string& fname) {
         if(m_printer) m_printer->save<Fmt>(fname);