SDL: Implement a hellish workaround to fix bug #3368143.

The bug in question is "SDL/OpenGL: Crash when switching renderer backend". To
fix it I added a stupid graphics state copying to the SDL backend, in case the
graphics manager is switched. The implementation of this is considered a pure
workaround, no one should ever do it like this in reality... I just want to
die when looking at this... Not sure why I actually committed it.

Anyway it at least makes the OpenGL backend testable for those who do not
want to fiddle with the config file directly.

2 files changed, 61 insertions, 2 deletions

diff --git a/backends/graphics/surfacesdl/surfacesdl-graphics.cpp b/backends/graphics/surfacesdl/surfacesdl-graphics.cpp
index 81c439e7e2..146200148a 100644
--- a/backends/graphics/surfacesdl/surfacesdl-graphics.cpp
+++ b/backends/graphics/surfacesdl/surfacesdl-graphics.cpp
@@ -249,7 +249,10 @@ void SurfaceSdlGraphicsManager::setFeatureState(OSystem::Feature f, bool enable)
 }
 
 bool SurfaceSdlGraphicsManager::getFeatureState(OSystem::Feature f) {
-	assert(_transactionMode == kTransactionNone);
+	// We need to allow this to be called from within a transaction, since we
+	// currently use it to retreive the graphics state, when switching from
+	// SDL->OpenGL mode for example.
+	//assert(_transactionMode == kTransactionNone);
 
 	switch (f) {
 	case OSystem::kFeatureFullscreenMode:
diff --git a/backends/platform/sdl/sdl.cpp b/backends/platform/sdl/sdl.cpp
index 63871f5034..ba57841256 100644
--- a/backends/platform/sdl/sdl.cpp
+++ b/backends/platform/sdl/sdl.cpp
@@ -49,6 +49,7 @@
 #include "backends/graphics/surfacesdl/surfacesdl-graphics.h"
 #ifdef USE_OPENGL
 #include "backends/graphics/openglsdl/openglsdl-graphics.h"
+#include "graphics/cursorman.cpp"
 #endif
 
 #include "icons/scummvm.xpm"
@@ -524,6 +525,22 @@ bool OSystem_SDL::setGraphicsMode(int mode) {
 		i = _sdlModesCount;
 	}
 
+	// Very hacky way to set up the old graphics manager state, in case we
+	// switch from SDL->OpenGL or OpenGL->SDL.
+	//
+	// This is a probably temporary workaround to fix bugs like #3368143
+	// "SDL/OpenGL: Crash when switching renderer backend".
+	const int screenWidth = _graphicsManager->getWidth();
+	const int screenHeight = _graphicsManager->getHeight();
+	const bool arState = _graphicsManager->getFeatureState(kFeatureAspectRatioCorrection);
+	const bool fullscreen = _graphicsManager->getFeatureState(kFeatureFullscreenMode);
+	const bool cursorPalette = _graphicsManager->getFeatureState(kFeatureCursorPalette);
+#ifdef USE_RGB_COLOR
+	const Graphics::PixelFormat pixelFormat = _graphicsManager->getScreenFormat();
+#endif
+
+	bool switchedManager = false;
+
 	// Loop through modes
 	while (srcMode->name) {
 		if (i == mode) {
@@ -535,16 +552,55 @@ bool OSystem_SDL::setGraphicsMode(int mode) {
 				_graphicsManager = new SurfaceSdlGraphicsManager(_eventSource);
 				((SurfaceSdlGraphicsManager *)_graphicsManager)->initEventObserver();
 				_graphicsManager->beginGFXTransaction();
+
+				switchedManager = true;
 			} else if (_graphicsMode < _sdlModesCount && mode >= _sdlModesCount) {
 				debug(1, "switching to OpenGL graphics");
 				delete _graphicsManager;
 				_graphicsManager = new OpenGLSdlGraphicsManager(_eventSource);
 				((OpenGLSdlGraphicsManager *)_graphicsManager)->initEventObserver();
 				_graphicsManager->beginGFXTransaction();
+
+				switchedManager = true;
 			}
 
 			_graphicsMode = mode;
-			return _graphicsManager->setGraphicsMode(srcMode->id);
+
+			if (switchedManager) {
+#ifdef USE_RGB_COLOR
+				_graphicsManager->initSize(screenWidth, screenHeight, &pixelFormat);
+#else
+				_graphicsManager->initSize(screenWidth, screenHeight, 0);
+#endif
+				_graphicsManager->setFeatureState(kFeatureAspectRatioCorrection, arState);
+				_graphicsManager->setFeatureState(kFeatureFullscreenMode, fullscreen);
+				_graphicsManager->setFeatureState(kFeatureCursorPalette, cursorPalette);
+
+				// Worst part about this right now, tell the cursor manager to
+				// resetup the cursor + cursor palette if necessarily
+
+				// First we need to try to setup the old state on the new manager...
+				if (_graphicsManager->endGFXTransaction() != kTransactionSuccess) {
+					// Oh my god if this failed the client code might just explode.
+					return false;
+				}
+
+				// Next setup the cursor again
+				CursorMan.pushCursor(0, 0, 0, 0, 0, 0);
+				CursorMan.popCursor();
+
+				// Next setup cursor palette if needed
+				if (cursorPalette) {
+					CursorMan.pushCursorPalette(0, 0, 0);
+					CursorMan.popCursorPalette();
+				}
+
+				_graphicsManager->beginGFXTransaction();
+				// Oh my god if this failed the client code might just explode.
+				return _graphicsManager->setGraphicsMode(srcMode->id);
+			} else {
+				return _graphicsManager->setGraphicsMode(srcMode->id);
+			}
 		}
 
 		i++;