I recently started work on a game project, and decided to use GLFW for windowing / OpenGL context handling. GLFW doesn't have support for creating message boxes / dialogs, and I was unable to find anything simple online to do the job, so I decided to take a shot at creating a library to do so.

I've completed a first iteration of the library (which I'm calling 'Boxer') that supports the creation of message boxes on OS X, Windows, and Linux (with GTK+). I've never released any code intended for reuse, and I'd love to get some feedback, specifically in C++ / library best practices.

There are four files: the header file and an implementation file for each OS. Everything is set up to be built with CMake.

Source

boxer.h

#ifndef BOXER_H
#define BOXER_H

namespace boxer {

enum class Style {
   Info,
   Warning,
   Error,
   Question
};

enum class Buttons {
   OK,
   OKCancel,
   YesNo
};

enum class Selection {
   OK,
   Cancel,
   Yes,
   No,
   None
};

const Style DEFAULT_STYLE = Style::Info;
const Buttons DEFAULT_BUTTONS = Buttons::OK;

Selection show(const char *message, const char *title, Style style, Buttons buttons);

inline Selection show(const char *message, const char *title, Style style) {
   return show(message, title, style, DEFAULT_BUTTONS);
}

inline Selection show(const char *message, const char *title, Buttons buttons) {
   return show(message, title, DEFAULT_STYLE, buttons);
}

inline Selection show(const char *message, const char *title) {
   return show(message, title, DEFAULT_STYLE, DEFAULT_BUTTONS);
}

} // namespace boxer

#endif

boxer_linux.cpp

#include <boxer/boxer.h>
#include <gtk/gtk.h>

namespace boxer {

namespace {

GtkMessageType getMessageType(Style style) {
   switch (style) {
      case Style::Info:
         return GTK_MESSAGE_INFO;
      case Style::Warning:
         return GTK_MESSAGE_WARNING;
      case Style::Error:
         return GTK_MESSAGE_ERROR;
      case Style::Question:
         return GTK_MESSAGE_QUESTION;
      default:
         return GTK_MESSAGE_INFO;
   }
}

GtkButtonsType getButtonsType(Buttons buttons) {
   switch (buttons) {
      case Buttons::OK:
         return GTK_BUTTONS_OK;
      case Buttons::OKCancel:
         return GTK_BUTTONS_OK_CANCEL;
      case Buttons::YesNo:
         return GTK_BUTTONS_YES_NO;
      default:
         return GTK_BUTTONS_OK;
   }
}

Selection getSelection(gint response) {
   switch (response) {
      case GTK_RESPONSE_OK:
         return Selection::OK;
      case GTK_RESPONSE_CANCEL:
         return Selection::Cancel;
      case GTK_RESPONSE_YES:
         return Selection::Yes;
      case GTK_RESPONSE_NO:
         return Selection::No;
      default:
         return Selection::None;
   }
}

} // namespace

Selection show(const char *message, const char *title, Style style, Buttons buttons) {
   if (!gtk_init_check(0, NULL)) {
      return Selection::None;
   }

   GtkWidget *dialog = gtk_message_dialog_new(NULL,
                                              GTK_DIALOG_MODAL,
                                              getMessageType(style),
                                              getButtonsType(buttons),
                                              "%s",
                                              message);
   gtk_window_set_title(GTK_WINDOW(dialog), title);
   Selection selection = getSelection(gtk_dialog_run(GTK_DIALOG(dialog)));

   gtk_widget_destroy(GTK_WIDGET(dialog));
   while (g_main_context_iteration(NULL, false));

   return selection;
}

} // namespace boxer

boxer_osx.mm

#include <boxer/boxer.h>
#import <Cocoa/Cocoa.h>

namespace boxer {

namespace {

NSString* const OK_STR = @"OK";
NSString* const CANCEL_STR = @"Cancel";
NSString* const YES_STR = @"Yes";
NSString* const NO_STR = @"No";

NSAlertStyle getAlertStyle(Style style) {
   switch (style) {
      case Style::Info:
         return NSInformationalAlertStyle;
      case Style::Warning:
         return NSWarningAlertStyle;
      case Style::Error:
         return NSCriticalAlertStyle;
      case Style::Question:
         return NSWarningAlertStyle;
      default:
         return NSInformationalAlertStyle;
   }
}

void setButtons(NSAlert *alert, Buttons buttons) {
   switch (buttons) {
      case Buttons::OK:
         [alert addButtonWithTitle:OK_STR];
         break;
      case Buttons::OKCancel:
         [alert addButtonWithTitle:OK_STR];
         [alert addButtonWithTitle:CANCEL_STR];
         break;
      case Buttons::YesNo:
         [alert addButtonWithTitle:YES_STR];
         [alert addButtonWithTitle:NO_STR];
         break;
      default:
         [alert addButtonWithTitle:OK_STR];
   }
}

Selection getSelection(int index, Buttons buttons) {
   switch (buttons) {
      case Buttons::OK:
         return index == NSAlertFirstButtonReturn ? Selection::OK : Selection::None;
      case Buttons::OKCancel:
         if (index == NSAlertFirstButtonReturn) {
            return Selection::OK;
         } else if (index == NSAlertSecondButtonReturn) {
            return Selection::Cancel;
         } else {
            return Selection::None;
         }
      case Buttons::YesNo:
         if (index == NSAlertFirstButtonReturn) {
            return Selection::Yes;
         } else if (index == NSAlertSecondButtonReturn) {
            return Selection::No;
         } else {
            return Selection::None;
         }
      default:
         return Selection::None;
   }
}

} // namespace

Selection show(const char *message, const char *title, Style style, Buttons buttons) {
   NSAlert *alert = [[NSAlert alloc] init];

   [alert setMessageText:[NSString stringWithCString:title
                                   encoding:[NSString defaultCStringEncoding]]];
   [alert setInformativeText:[NSString stringWithCString:message
                                       encoding:[NSString defaultCStringEncoding]]];

   [alert setAlertStyle:getAlertStyle(style)];
   setButtons(alert, buttons);

   Selection selection = getSelection([alert runModal], buttons);
   [alert release];

   return selection;
}

} // namespace boxer

boxer_win.cpp

#include <boxer/boxer.h>
#include <windows.h>

namespace boxer {

namespace {

UINT getIcon(Style style) {
   switch (style) {
      case Style::Info:
         return MB_ICONINFORMATION;
      case Style::Warning:
         return MB_ICONWARNING;
      case Style::Error:
         return MB_ICONERROR;
      case Style::Question:
         return MB_ICONQUESTION;
      default:
         return MB_ICONINFORMATION;
   }
}

UINT getButtons(Buttons buttons) {
   switch (buttons) {
      case Buttons::OK:
         return MB_OK;
      case Buttons::OKCancel:
         return MB_OKCANCEL;
      case Buttons::YesNo:
         return MB_YESNO;
      default:
         return MB_OK;
   }
}

Selection getSelection(int response) {
   switch (response) {
      case IDOK:
         return Selection::OK;
      case IDCANCEL:
         return Selection::Cancel;
      case IDYES:
         return Selection::Yes;
      case IDNO:
         return Selection::No;
      default:
         return Selection::None;
   }
}

} // namespace

Selection show(const char *message, const char *title, Style style, Buttons buttons) {
   UINT flags = MB_TASKMODAL;

   flags |= getIcon(style);
   flags |= getButtons(buttons);

   return getSelection(MessageBox(NULL, message, title, flags));
}

} // namespace boxer

Example

Here is an example program that uses Boxer:

#include <boxer/boxer.h>

int main(int argc, char *argv[]) {
   boxer::show("Simple message boxes are very easy to create.", "Simple Example");

   boxer::show("There are a few different message box styles to choose from.", "Style Example", boxer::Style::Error);

   boxer::Selection selection;
   do {
      selection = boxer::show("Different buttons may be used, and the user's selection can be checked. Would you like to see this message again?", "Selection Example", boxer::Style::Question, boxer::Buttons::YesNo);
   } while (selection == boxer::Selection::Yes);

   return 0;
}