Codechange: [SDL2] Split Start() in a few more functions

This makes it a bit easier to follow what is going on, and
allow future subdrivers to hook into a few of these functions.

Reworked the code slighly while at it, to return early where
possible.

src/video/sdl2_v.cpp

@@ -673,28 +673,40 @@ int VideoDriver_SDL::PollEvent()
 	return -1;
 }
 
-const char *VideoDriver_SDL::Start(const StringList &parm)
+static const char *InitializeSDL()
 {
-	if (BlitterFactory::GetCurrentBlitter()->GetScreenDepth() == 0) return "Only real blitters supported";
-
 	/* Explicitly disable hardware acceleration. Enabling this causes
 	 * UpdateWindowSurface() to update the window's texture instead of
 	 * its surface. */
 	SDL_SetHint(SDL_HINT_FRAMEBUFFER_ACCELERATION, "0");
 	SDL_SetHint(SDL_HINT_MOUSE_RELATIVE_MODE_WARP, "1");
 
-	/* Just on the offchance the audio subsystem started before the video system,
-	 * check whether any part of SDL has been initialised before getting here.
-	 * Slightly duplicated with sound/sdl_s.cpp */
-	int ret_code = 0;
-	if (SDL_WasInit(SDL_INIT_VIDEO) == 0) {
-		ret_code = SDL_InitSubSystem(SDL_INIT_VIDEO);
-	}
-	if (ret_code < 0) return SDL_GetError();
+	/* Check if the video-driver is already initialized. */
+	if (SDL_WasInit(SDL_INIT_VIDEO) != 0) return nullptr;
 
+	if (SDL_InitSubSystem(SDL_INIT_VIDEO) < 0) return SDL_GetError();
+	return nullptr;
+}
+
+const char *VideoDriver_SDL::Initialize()
+{
 	this->UpdateAutoResolution();
 
+	const char *error = InitializeSDL();
+	if (error != nullptr) return error;
+
 	FindResolutions();
+	DEBUG(driver, 2, "Resolution for display: %ux%u", _cur_resolution.width, _cur_resolution.height);
+
+	return nullptr;
+}
+
+const char *VideoDriver_SDL::Start(const StringList &parm)
+{
+	if (BlitterFactory::GetCurrentBlitter()->GetScreenDepth() == 0) return "Only real blitters supported";
+
+	const char *error = this->Initialize();
+	if (error != nullptr) return error;
 
 	this->startup_display = FindStartupDisplay(GetDriverParamInt(parm, "display", -1));
 

src/video/sdl2_v.h

@@ -56,6 +56,7 @@ private:
 	void MainLoopCleanup();
 	bool CreateMainSurface(uint w, uint h, bool resize);
 	bool CreateMainWindow(uint w, uint h);
+	const char *Initialize();
 
 #ifdef __EMSCRIPTEN__
 	/* Convert a constant pointer back to a non-constant pointer to a member function. */