desktop-ui: improve terminal support on windows

Previously, terminal (console) support on Windows required opting in at
compile time. Now, the runtime behavior is largely the same regardless
of how ares is compiled.

- ares will attach to the terminal of the parent process (if present) by
  default and redirect any unset stdio streams.
- If the --terminal argument is provided, ares will always create a new
  terminal window and stdio will be redirected to it.
- Otherwise, if stdio handles were already valid on launch they will be
  left alone (to support redirection to/from files).

desktop-ui/desktop-ui.cpp

@@ -39,6 +39,11 @@ auto locate(const string& name) -> string {
 
 #include <nall/main.hpp>
 auto nall::main(Arguments arguments) -> void {
+#if defined(PLATFORM_WINDOWS)
+  bool createTerminal = arguments.take("--terminal");
+  terminal::redirectStdioToTerminal(createTerminal);
+#endif
+
   Application::setName("ares");
   Application::setScreenSaver(false);
 
@@ -74,6 +79,9 @@ auto nall::main(Arguments arguments) -> void {
     print("Usage: ares [OPTIONS]... game\n\n");
     print("Options:\n");
     print("  --help               Displays available options and exit\n");
+#if defined(PLATFORM_WINDOWS)
+    print("  --terminal           Create new terminal window\n");
+#endif
     print("  --fullscreen         Start in full screen mode\n");
     print("  --system name        Specifiy the system name\n");
     print("\n");

nall/nall.cpp

@@ -16,6 +16,7 @@
 #include <nall/platform.cpp>
 #include <nall/random.cpp>
 #include <nall/run.cpp>
+#include <nall/terminal.cpp>
 #include <nall/thread.cpp>
 //currently unused by ares
 //#include <nall/smtp.cpp>

nall/terminal.cpp

@@ -0,0 +1,21 @@
+#include <nall/terminal.hpp>
+
+namespace nall::terminal {
+
+NALL_HEADER_INLINE auto redirectStdioToTerminal(bool create) -> void {
+#if defined(PLATFORM_WINDOWS)
+  if(create) {
+    FreeConsole();
+    if(!AllocConsole()) return;
+  } else if(!AttachConsole(ATTACH_PARENT_PROCESS)) {
+    return;
+  }
+
+  //unless a new terminal was requested, do not reopen already valid handles (allow redirection to/from file)
+  if(create || _get_osfhandle(_fileno(stdin )) < 0) freopen("CONIN$" , "r", stdin );
+  if(create || _get_osfhandle(_fileno(stdout)) < 0) freopen("CONOUT$", "w", stdout);
+  if(create || _get_osfhandle(_fileno(stderr)) < 0) freopen("CONOUT$", "w", stderr);
+#endif
+}
+
+}

nall/terminal.hpp

@@ -4,6 +4,8 @@
 
 namespace nall::terminal {
 
+auto redirectStdioToTerminal(bool create) -> void;
+
 inline auto escapable() -> bool {
   #if defined(PLATFORM_WINDOWS)
   //todo: colors are supported by Windows 10+ and with alternate terminals (eg msys)
@@ -63,3 +65,7 @@ template<typename... P> inline auto gray(P&&... p) -> string {
 }
 
 }
+
+#if defined(NALL_HEADER_ONLY)
+  #include <nall/terminal.cpp>
+#endif