SDL: Do not reset window size when engines update rendering surface

This change allows:

* Engines to update their target rendering surface/size and pixel
  format with the backend multiple times during gameplay;
* Users to resize the ScummVM window without having it reset
  size/position every time an engine updates its target surface
  format;
* Conversions/scaling to continue to run efficiently in hardware,
  instead of requiring engines to pick their maximum possible
  output format once and upscale inefficiently in software;
* The window to reset size once when an engine calls to set its
  initial output size, and to reset again once ScummVM returns to
  the launcher.

This is relevant for at least SCI32 and DreamWeb engines, which
perform graphics mode switches during games.

2 files changed, 10 insertions, 4 deletions

diff --git a/backends/platform/sdl/sdl.cpp b/backends/platform/sdl/sdl.cpp
index bbd5c89f80..f44d87666a 100644
--- a/backends/platform/sdl/sdl.cpp
+++ b/backends/platform/sdl/sdl.cpp
@@ -297,20 +297,28 @@ void OSystem_SDL::initBackend() {
 	dynamic_cast<SdlGraphicsManager *>(_graphicsManager)->activateManager();
 }
 
-#if defined(USE_TASKBAR)
 void OSystem_SDL::engineInit() {
+#if SDL_VERSION_ATLEAST(2, 0, 0)
+	dynamic_cast<SdlGraphicsManager *>(_graphicsManager)->unlockWindowSize();
+#endif
+#ifdef USE_TASKBAR
 	// Add the started engine to the list of recent tasks
 	_taskbarManager->addRecent(ConfMan.getActiveDomainName(), ConfMan.get("description"));
 
 	// Set the overlay icon the current running engine
 	_taskbarManager->setOverlayIcon(ConfMan.getActiveDomainName(), ConfMan.get("description"));
+#endif
 }
 
 void OSystem_SDL::engineDone() {
+#if SDL_VERSION_ATLEAST(2, 0, 0)
+	dynamic_cast<SdlGraphicsManager *>(_graphicsManager)->unlockWindowSize();
+#endif
+#ifdef USE_TASKBAR
 	// Remove overlay icon
 	_taskbarManager->setOverlayIcon("", "");
-}
 #endif
+}
 
 void OSystem_SDL::initSDL() {
 	// Check if SDL has not been initialized
diff --git a/backends/platform/sdl/sdl.h b/backends/platform/sdl/sdl.h
index bc4292be0b..61513fa65f 100644
--- a/backends/platform/sdl/sdl.h
+++ b/backends/platform/sdl/sdl.h
@@ -59,10 +59,8 @@ public:
 
 	// Override functions from ModularBackend and OSystem
 	virtual void initBackend();
-#if defined(USE_TASKBAR)
 	virtual void engineInit();
 	virtual void engineDone();
-#endif
 	virtual void quit();
 	virtual void fatalError();