implement swapping the position of both screens

closes #855

src/frontend/FrontendUtil.h

@@ -120,7 +120,8 @@ void EnableCheats(bool enable);
 //     2 = emphasize bottom screen
 // * screenGap: size of the gap between the two screens
 // * integerScale: force screens to be scaled up at integer scaling factors
-void SetupScreenLayout(int screenWidth, int screenHeight, int screenLayout, int rotation, int sizing, int screenGap, bool integerScale);
+// * screenSwap: whether to swap the position of both screens
+void SetupScreenLayout(int screenWidth, int screenHeight, int screenLayout, int rotation, int sizing, int screenGap, bool integerScale, int swapScreens);
 
 // get a 2x3 transform matrix for each screen
 // note: the transform assumes an origin point at the top left of the display,

src/frontend/Util_Video.cpp

@@ -109,7 +109,7 @@ void M23_Transform(float* m, float& x, float& y)
 }
 
 
-void SetupScreenLayout(int screenWidth, int screenHeight, int screenLayout, int rotation, int sizing, int screenGap, bool integerScale)
+void SetupScreenLayout(int screenWidth, int screenHeight, int screenLayout, int rotation, int sizing, int screenGap, bool integerScale, int swapScreens)
 {
     float refpoints[4][2] =
     {
@@ -152,7 +152,7 @@ void SetupScreenLayout(int screenWidth, int screenHeight, int screenLayout, int
             (((layout == 0 && (rotation % 2 == 0)) || (layout == 1 && (rotation % 2 == 1))
                 ? 192.f : 256.f)
             + screenGap) / 2.f;
-        if (rotation == 1 || rotation == 2)
+        if ((rotation == 1 || rotation == 2) ^ swapScreens)
             offset *= -1.f;
 
         M23_Translate(TopScreenMtx, (idx==0)?-offset:0, (idx==1)?-offset:0);

src/frontend/qt_sdl/PlatformConfig.cpp

@@ -39,6 +39,7 @@ int WindowMaximized;
 int ScreenRotation;
 int ScreenGap;
 int ScreenLayout;
+int ScreenSwap;
 int ScreenSizing;
 int IntegerScaling;
 int ScreenFilter;
@@ -135,6 +136,7 @@ ConfigEntry PlatformConfigFile[] =
     {"ScreenRotation", 0, &ScreenRotation, 0, NULL, 0},
     {"ScreenGap",      0, &ScreenGap,      0, NULL, 0},
     {"ScreenLayout",   0, &ScreenLayout,   0, NULL, 0},
+    {"ScreenSwap",     0, &ScreenSwap,     0, NULL, 0},
     {"ScreenSizing",   0, &ScreenSizing,   0, NULL, 0},
     {"IntegerScaling", 0, &IntegerScaling, 0, NULL, 0},
     {"ScreenFilter",   0, &ScreenFilter,   1, NULL, 0},

src/frontend/qt_sdl/PlatformConfig.h

@@ -53,6 +53,7 @@ extern int WindowMaximized;
 extern int ScreenRotation;
 extern int ScreenGap;
 extern int ScreenLayout;
+extern int ScreenSwap;
 extern int ScreenSizing;
 extern int IntegerScaling;
 extern int ScreenFilter;

src/frontend/qt_sdl/main.cpp

@@ -647,7 +647,8 @@ void ScreenHandler::screenSetupLayout(int w, int h)
                                 Config::ScreenRotation,
                                 sizing,
                                 Config::ScreenGap,
-                                Config::IntegerScaling != 0);
+                                Config::IntegerScaling != 0,
+                                Config::ScreenSwap != 0);
 
     Frontend::GetScreenTransforms(screenMatrix[0], screenMatrix[1]);
 }
@@ -1232,6 +1233,12 @@ MainWindow::MainWindow(QWidget* parent) : QMainWindow(parent)
             }
 
             connect(grpScreenLayout, &QActionGroup::triggered, this, &MainWindow::onChangeScreenLayout);
+        
+            submenu->addSeparator();
+
+            actScreenSwap = submenu->addAction("Swap screens");
+            actScreenSwap->setCheckable(true);
+            connect(actScreenSwap, &QAction::triggered, this, &MainWindow::onChangeScreenSwap);
         }
         {
             QMenu* submenu = menu->addMenu("Screen sizing");
@@ -1315,6 +1322,8 @@ MainWindow::MainWindow(QWidget* parent) : QMainWindow(parent)
     actScreenSizing[Config::ScreenSizing]->setChecked(true);
     actIntegerScaling->setChecked(Config::IntegerScaling != 0);
 
+    actScreenSwap->setChecked(Config::ScreenSwap != 0);
+
     actScreenFiltering->setChecked(Config::ScreenFilter != 0);
     actShowOSD->setChecked(Config::ShowOSD != 0);
 
@@ -2049,6 +2058,13 @@ void MainWindow::onChangeScreenLayout(QAction* act)
     emit screenLayoutChange();
 }
 
+void MainWindow::onChangeScreenSwap(bool checked)
+{
+    Config::ScreenSwap = checked?1:0;
+
+    emit screenLayoutChange();
+}
+
 void MainWindow::onChangeScreenSizing(QAction* act)
 {
     int sizing = act->data().toInt();

src/frontend/qt_sdl/main.h

@@ -222,6 +222,7 @@ private slots:
     void onChangeScreenRotation(QAction* act);
     void onChangeScreenGap(QAction* act);
     void onChangeScreenLayout(QAction* act);
+    void onChangeScreenSwap(bool checked);
     void onChangeScreenSizing(QAction* act);
     void onChangeIntegerScaling(bool checked);
     void onChangeScreenFiltering(bool checked);
@@ -279,6 +280,7 @@ public:
     QAction* actScreenGap[6];
     QActionGroup* grpScreenLayout;
     QAction* actScreenLayout[3];
+    QAction* actScreenSwap;
     QActionGroup* grpScreenSizing;
     QAction* actScreenSizing[4];
     QAction* actIntegerScaling;