Eliminate blocking in Error() and Message() calls.

This serves two purposes.

First, we want to (some day) convert these messages into a less
obtrustive form, something like toaster notifications, such that they
don't interrupt workflow as harshly. That would, of course, be
nonblocking.

Second, some platforms, like Emscripten, do not support nested event
loops, and it's not possible to display a modal dialog on them
synchronously.

When making this commit, I've reviewed all Error() and Message()
calls to ensure that only some of the following is true for all
of them:
  * The call is followed a break or return statement that exits
    an UI entry point (e.g. an MenuX function);
  * The call is followed by cleanup (in fact, in this case the new
    behavior is better, since even with a synchronous modal dialog
    we have to be reentrant);
  * The message is an informational message only and nothing
    unexpected will happen if the operation proceeds in background.

In general, all Error() calls already satisfied the above conditions,
although in some cases I changed control flow aroudn them to more
clearly show that. The Message() calls that didn't satisfy these
conditions were reworked into an asynchronous form.

There are three explicit RunModal() calls left that need to be
reworked into an async form.

src/confscreen.cpp

@@ -331,10 +331,10 @@ bool TextWindow::EditControlDoneForConfiguration(const std::string &s) {
             double x, y, z;
             if(sscanf(s.c_str(), "%lf, %lf, %lf", &x, &y, &z)==3) {
                 SS.lightDir[edit.i] = Vector::From(x, y, z);
+                SS.GW.Invalidate();
             } else {
                 Error(_("Bad format: specify coordinates as x, y, z"));
             }
-            SS.GW.Invalidate();
             break;
         }
         case Edit::COLOR: {
@@ -367,11 +367,11 @@ bool TextWindow::EditControlDoneForConfiguration(const std::string &s) {
         }
         case Edit::CAMERA_TANGENT: {
             SS.cameraTangent = (min(2.0, max(0.0, atof(s.c_str()))))/1000.0;
+            SS.GW.Invalidate();
             if(!SS.usePerspectiveProj) {
                 Message(_("The perspective factor will have no effect until you "
                           "enable View -> Use Perspective Projection."));
             }
-            SS.GW.Invalidate();
             break;
         }
         case Edit::GRID_SPACING: {
@@ -385,8 +385,8 @@ bool TextWindow::EditControlDoneForConfiguration(const std::string &s) {
                 Error(_("Specify between 0 and 8 digits after the decimal."));
             } else {
                 SS.SetUnitDigitsAfterDecimal(v);
+                SS.GW.Invalidate();
             }
-            SS.GW.Invalidate();
             break;
         }
         case Edit::EXPORT_SCALE: {

src/file.cpp

@@ -844,6 +844,7 @@ static Platform::MessageDialog::Response LocateImportedFile(const Platform::Path
         dialog->AddButton(C_("button", "&Cancel"), MessageDialog::Response::CANCEL);
     }
 
+    // FIXME(async): asyncify this call
     return dialog->RunModal();
 }
 

src/graphicswin.cpp

@@ -678,24 +678,24 @@ void GraphicsWindow::MenuView(Command id) {
 
         case Command::SHOW_GRID:
             SS.GW.showSnapGrid = !SS.GW.showSnapGrid;
+            SS.GW.EnsureValidActives();
+            SS.GW.Invalidate();
             if(SS.GW.showSnapGrid && !SS.GW.LockedInWorkplane()) {
                 Message(_("No workplane is active, so the grid will not appear."));
             }
-            SS.GW.EnsureValidActives();
-            SS.GW.Invalidate();
             break;
 
         case Command::PERSPECTIVE_PROJ:
             SS.usePerspectiveProj = !SS.usePerspectiveProj;
+            SS.GW.EnsureValidActives();
+            SS.GW.Invalidate();
             if(SS.cameraTangent < 1e-6) {
                 Error(_("The perspective factor is set to zero, so the view will "
                         "always be a parallel projection.\n\n"
                         "For a perspective projection, modify the perspective "
                         "factor in the configuration screen. A value around 0.3 "
                         "is typical."));
             }
-            SS.GW.EnsureValidActives();
-            SS.GW.Invalidate();
             break;
 
         case Command::ONTO_WORKPLANE:
@@ -1050,11 +1050,11 @@ void GraphicsWindow::MenuEdit(Command id) {
                     }
                 }
             } while(didSomething);
+            SS.GW.Invalidate();
+            SS.ScheduleShowTW();
             if(newlySelected == 0) {
                 Error(_("No additional entities share endpoints with the selected entities."));
             }
-            SS.GW.Invalidate();
-            SS.ScheduleShowTW();
             break;
         }
 
@@ -1077,7 +1077,6 @@ void GraphicsWindow::MenuEdit(Command id) {
                 break;
             }
 
-
             SS.UndoRemember();
             // Rotate by ninety degrees about the coordinate axis closest
             // to the screen normal.
@@ -1168,20 +1167,18 @@ void GraphicsWindow::MenuRequest(Command id) {
             } else if(g->type == Group::Type::DRAWING_WORKPLANE) {
                 // The group's default workplane
                 g->activeWorkplane = g->h.entity(0);
-                Message(_("No workplane selected. Activating default workplane "
-                          "for this group."));
-            }
-
-            if(!SS.GW.LockedInWorkplane()) {
+                MessageAndRun([] {
+                    // Align the view with the selected workplane
+                    SS.GW.ClearSuper();
+                    SS.GW.AnimateOntoWorkplane();
+                }, _("No workplane selected. Activating default workplane "
+                     "for this group."));
+            } else {
                 Error(_("No workplane is selected, and the active group does "
                         "not have a default workplane. Try selecting a "
                         "workplane, or activating a sketch-in-new-workplane "
                         "group."));
-                break;
             }
-            // Align the view with the selected workplane
-            SS.GW.ClearSuper();
-            SS.GW.AnimateOntoWorkplane();
             break;
         }
         case Command::FREE_IN_3D:
@@ -1232,12 +1229,13 @@ void GraphicsWindow::MenuRequest(Command id) {
             break;
 
         case Command::CONSTRUCTION: {
-            SS.UndoRemember();
             SS.GW.GroupSelection();
             if(SS.GW.gs.entities == 0) {
                 Error(_("No entities are selected. Select entities before "
                         "trying to toggle their construction state."));
+                break;
             }
+            SS.UndoRemember();
             int i;
             for(i = 0; i < SS.GW.gs.entities; i++) {
                 hEntity he = SS.GW.gs.entity[i];

src/importdxf.cpp

@@ -1100,6 +1100,7 @@ static void ImportDwgDxf(const Platform::Path &filename,
     importer.clearBlockTransform();
     if(!read(data, &importer)) {
         Error("Corrupted %s file.", fileType.c_str());
+        return;
     }
     if(importer.unknownEntities > 0) {
         Message("%u %s entities of unknown type were ignored.",

src/modify.cpp

@@ -711,6 +711,7 @@ void GraphicsWindow::SplitLinesOrCurves() {
         }
     } else {
         Error(_("Can't split; no intersection found."));
+        return;
     }
 
     // All done, clean up and regenerate.

src/platform/gui.h

@@ -213,7 +213,7 @@ class Window {
     std::function<void()>               onClose;
     std::function<void(bool)>           onFullScreen;
     std::function<bool(MouseEvent)>     onMouseEvent;
-    std::function<void(SixDofEvent)>  onSixDofEvent;
+    std::function<void(SixDofEvent)>    onSixDofEvent;
     std::function<bool(KeyboardEvent)>  onKeyboardEvent;
     std::function<void(std::string)>    onEditingDone;
     std::function<void(double)>         onScrollbarAdjusted;
@@ -293,6 +293,8 @@ class MessageDialog {
         CANCEL
     };
 
+    std::function<void(Response)> onResponse;
+
     virtual ~MessageDialog() {}
 
     virtual void SetType(Type type) = 0;
@@ -303,6 +305,12 @@ class MessageDialog {
     virtual void AddButton(std::string name, Response response, bool isDefault = false) = 0;
 
     virtual Response RunModal() = 0;
+    virtual void ShowModal() {
+        Response response = RunModal();
+        if(onResponse) {
+            onResponse(response);
+        }
+    }
 };
 
 typedef std::shared_ptr<MessageDialog> MessageDialogRef;

src/platform/guigtk.cpp

@@ -1078,7 +1078,11 @@ class MessageDialogImplGtk final : public MessageDialog {
         : gtkDialog(parent, "", /*use_markup=*/false, Gtk::MESSAGE_INFO,
                     Gtk::BUTTONS_NONE, /*modal=*/true)
     {
-         SetTitle("Message");
+        SetTitle("Message");
+
+        gtkDialog.signal_response().connect([this](int gtkResponse) {
+            ProcessResponse(gtkResponse);
+        });
     }
 
     void SetType(Type type) override {
@@ -1129,21 +1133,35 @@ class MessageDialogImplGtk final : public MessageDialog {
         }
     }
 
-    Response RunModal() override {
-        switch(gtkDialog.run()) {
-            case Gtk::RESPONSE_OK:     return Response::OK;     break;
-            case Gtk::RESPONSE_YES:    return Response::YES;    break;
-            case Gtk::RESPONSE_NO:     return Response::NO;     break;
-            case Gtk::RESPONSE_CANCEL: return Response::CANCEL; break;
+    Response ProcessResponse(int gtkResponse) {
+        Response response;
+        switch(gtkResponse) {
+            case Gtk::RESPONSE_OK:     response = Response::OK;     break;
+            case Gtk::RESPONSE_YES:    response = Response::YES;    break;
+            case Gtk::RESPONSE_NO:     response = Response::NO;     break;
+            case Gtk::RESPONSE_CANCEL: response = Response::CANCEL; break;
 
             case Gtk::RESPONSE_NONE:
             case Gtk::RESPONSE_CLOSE:
             case Gtk::RESPONSE_DELETE_EVENT:
-                return Response::NONE;
+                response = Response::NONE;
                 break;
 
             default: ssassert(false, "Unexpected response");
         }
+
+        if(onResponse) {
+            onResponse(response);
+        }
+        return response;
+    }
+
+    void ShowModal() override {
+        gtkDialog.show();
+    }
+
+    Response RunModal() override {
+        return gtkDialog.run();
     }
 };
 

src/solvespace.cpp

@@ -161,6 +161,7 @@ bool SolveSpaceUI::LoadAutosaveFor(const Platform::Path &filename) {
                       /*isDefault=*/true);
     dialog->AddButton(C_("button", "Do&n't Load"), MessageDialog::Response::NO);
 
+    // FIXME(async): asyncify this call
     if(dialog->RunModal() == MessageDialog::Response::YES) {
         unsaved = true;
         return LoadFromFile(autosaveFile, /*canCancel=*/true);
@@ -463,6 +464,7 @@ bool SolveSpaceUI::OkayToStartNewFile() {
     dialog->AddButton(C_("button", "Do&n't Save"), MessageDialog::Response::NO);
     dialog->AddButton(C_("button", "&Cancel"), MessageDialog::Response::CANCEL);
 
+    // FIXME(async): asyncify this call
     switch(dialog->RunModal()) {
         case MessageDialog::Response::YES:
             return GetFilenameAndSave(/*saveAs=*/false);

src/solvespace.h

@@ -235,6 +235,7 @@ void MultMatrix(double *mata, double *matb, double *matr);
 
 int64_t GetMilliseconds();
 void Message(const char *fmt, ...);
+void MessageAndRun(std::function<void()> onDismiss, const char *fmt, ...);
 void Error(const char *fmt, ...);
 
 class System {

src/util.cpp

@@ -100,10 +100,11 @@ void SolveSpace::MultMatrix(double *mata, double *matb, double *matr) {
 }
 
 //-----------------------------------------------------------------------------
-// Word-wrap the string for our message box appropriately, and then display
+// Format the string for our message box appropriately, and then display
 // that string.
 //-----------------------------------------------------------------------------
-static void MessageBox(const char *fmt, va_list va, bool error)
+static void MessageBox(const char *fmt, va_list va, bool error,
+                       std::function<void()> onDismiss = std::function<void()>())
 {
 #ifndef LIBRARY
     va_list va_size;
@@ -156,7 +157,13 @@ static void MessageBox(const char *fmt, va_list va, bool error)
     }
     dialog->AddButton(C_("button", "&OK"), MessageDialog::Response::OK,
                       /*isDefault=*/true);
-    dialog->RunModal();
+
+    dialog->onResponse = [=](MessageDialog::Response _response) {
+        if(onDismiss) {
+            onDismiss();
+        }
+    };
+    dialog->ShowModal();
 #endif
 }
 void SolveSpace::Error(const char *fmt, ...)
@@ -173,6 +180,13 @@ void SolveSpace::Message(const char *fmt, ...)
     MessageBox(fmt, f, /*error=*/false);
     va_end(f);
 }
+void SolveSpace::MessageAndRun(std::function<void()> onDismiss, const char *fmt, ...)
+{
+    va_list f;
+    va_start(f, fmt);
+    MessageBox(fmt, f, /*error=*/false, onDismiss);
+    va_end(f);
+}
 
 //-----------------------------------------------------------------------------
 // Solve a mostly banded matrix. In a given row, there are LEFT_OF_DIAG