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.

6 files changed, 58 insertions, 18 deletions

diff --git a/backends/graphics/openglsdl/openglsdl-graphics.cpp b/backends/graphics/openglsdl/openglsdl-graphics.cpp
index f664314862..efc10a0d2c 100644
--- a/backends/graphics/openglsdl/openglsdl-graphics.cpp
+++ b/backends/graphics/openglsdl/openglsdl-graphics.cpp
@@ -509,16 +509,8 @@ bool OpenGLSdlGraphicsManager::setupMode(uint width, uint height) {
 	SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, _glContextMajor);
 	SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, _glContextMinor);
 
-	if (!_window->createOrUpdateWindow(width, height, flags)) {
-		// We treat fullscreen requests as a "hint" for now. This means in
-		// case it is not available we simply ignore it.
-		if (_wantsFullScreen) {
-			_window->createOrUpdateWindow(width, height, SDL_WINDOW_OPENGL | SDL_WINDOW_RESIZABLE);
-		}
-
-		if (!_window->getSDLWindow()) {
-			return false;
-		}
+	if (!createOrUpdateWindow(width, height, flags)) {
+		return false;
 	}
 
 	_glContext = SDL_GL_CreateContext(_window->getSDLWindow());
diff --git a/backends/graphics/sdl/sdl-graphics.cpp b/backends/graphics/sdl/sdl-graphics.cpp
index a13ca45477..aa6087beae 100644
--- a/backends/graphics/sdl/sdl-graphics.cpp
+++ b/backends/graphics/sdl/sdl-graphics.cpp
@@ -21,13 +21,16 @@
  */
 
 #include "backends/graphics/sdl/sdl-graphics.h"
-
 #include "backends/platform/sdl/sdl-sys.h"
 #include "backends/events/sdl/sdl-events.h"
 #include "common/textconsole.h"
 
 SdlGraphicsManager::SdlGraphicsManager(SdlEventSource *source, SdlWindow *window)
-	: _eventSource(source), _window(window) {
+	: _eventSource(source), _window(window)
+#if SDL_VERSION_ATLEAST(2, 0, 0)
+	, _allowWindowSizeReset(false), _lastFlags(0)
+#endif
+	  {
 }
 
 SdlGraphicsManager::~SdlGraphicsManager() {
@@ -73,3 +76,26 @@ bool SdlGraphicsManager::setState(const State &state) {
 	}
 }
 
+#if SDL_VERSION_ATLEAST(2, 0, 0)
+bool SdlGraphicsManager::createOrUpdateWindow(const int width, const int height, const Uint32 flags) {
+	if (!_window) {
+		return false;
+	}
+
+	// We only update the actual window when flags change (which usually means
+	// fullscreen mode is entered/exited) or when updates are forced so that we
+	// do not reset the window size whenever a game makes a call to change the
+	// size or pixel format of the internal game surface (since a user may have
+	// resized the game window)
+	if (!_window->getSDLWindow() || _lastFlags != flags || _allowWindowSizeReset) {
+		if (!_window->createOrUpdateWindow(width, height, flags)) {
+			return false;
+		}
+
+		_lastFlags = flags;
+		_allowWindowSizeReset = false;
+	}
+
+	return true;
+}
+#endif
diff --git a/backends/graphics/sdl/sdl-graphics.h b/backends/graphics/sdl/sdl-graphics.h
index 7f8790a9b4..937beef9b4 100644
--- a/backends/graphics/sdl/sdl-graphics.h
+++ b/backends/graphics/sdl/sdl-graphics.h
@@ -123,6 +123,17 @@ public:
 	SdlWindow *getWindow() const { return _window; }
 
 protected:
+#if SDL_VERSION_ATLEAST(2, 0, 0)
+public:
+	void unlockWindowSize() { _allowWindowSizeReset = true; }
+
+protected:
+	Uint32 _lastFlags;
+	bool _allowWindowSizeReset;
+
+	bool createOrUpdateWindow(const int width, const int height, const Uint32 flags);
+#endif
+
 	SdlEventSource *_eventSource;
 	SdlWindow *_window;
 };
diff --git a/backends/graphics/surfacesdl/surfacesdl-graphics.cpp b/backends/graphics/surfacesdl/surfacesdl-graphics.cpp
index 983b71ab28..cd7e11b32d 100644
--- a/backends/graphics/surfacesdl/surfacesdl-graphics.cpp
+++ b/backends/graphics/surfacesdl/surfacesdl-graphics.cpp
@@ -784,9 +784,14 @@ void SurfaceSdlGraphicsManager::initSize(uint w, uint h, const Graphics::PixelFo
 	}
 #endif
 
-	// Avoid redundant res changes
+#if !SDL_VERSION_ATLEAST(2, 0, 0)
+	// Avoid redundant res changes, only in SDL1. In SDL2, redundancies may not
+	// actually be redundant if ScummVM is switching between game engines and
+	// the screen dimensions are being reinitialized, since window resizing is
+	// supposed to reset when this happens
 	if ((int)w == _videoMode.screenWidth && (int)h == _videoMode.screenHeight)
 		return;
+#endif
 
 	_videoMode.screenWidth = w;
 	_videoMode.screenHeight = h;
@@ -2797,7 +2802,7 @@ SDL_Surface *SurfaceSdlGraphicsManager::SDL_SetVideoMode(int width, int height,
 		createWindowFlags |= SDL_WINDOW_FULLSCREEN_DESKTOP;
 	}
 
-	if (!_window->createOrUpdateWindow(width, height, createWindowFlags)) {
+	if (!createOrUpdateWindow(width, height, createWindowFlags)) {
 		return nullptr;
 	}
 
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();