IPHONE: Implement very basic GFX transaction support.

This allows for AR ratio correction changes to take place, even when the AR
setting is set after initSize for example.

backends/platform/iphone/osys_main.h

@@ -121,6 +121,10 @@ class OSystem_IPHONE : public EventsBaseBackend, public PaletteManager {
 	virtual bool setGraphicsMode(int mode);
 	virtual int getGraphicsMode() const;
 	virtual void initSize(uint width, uint height, const Graphics::PixelFormat *format);
+
+	virtual void beginGFXTransaction();
+	virtual TransactionError endGFXTransaction();
+
 	virtual int16 getHeight();
 	virtual int16 getWidth();
 

backends/platform/iphone/osys_video.mm

@@ -44,7 +44,6 @@
 	case kGraphicsModeNone:
 	case kGraphicsModeLinear:
 		_videoContext->graphicsMode = (GraphicsModes)mode;
-		[g_iPhoneViewInstance performSelectorOnMainThread:@selector(setGraphicsMode) withObject:nil waitUntilDone: YES];
 		return true;
 
 	default:
@@ -68,17 +67,21 @@
 	_gameScreenRaw = (byte *)malloc(width * height);
 	bzero(_gameScreenRaw, width * height);
 
-	updateOutputSurface();
-
-	clearOverlay();
-
 	_fullScreenIsDirty = false;
 	dirtyFullScreen();
-	_videoContext->mouseIsVisible = false;
 	_mouseCursorPaletteEnabled = false;
+}
+
+void OSystem_IPHONE::beginGFXTransaction() {
+}
+
+OSystem::TransactionError OSystem_IPHONE::endGFXTransaction() {
 	_screenChangeCount++;
+	updateOutputSurface();
+	[g_iPhoneViewInstance performSelectorOnMainThread:@selector(setGraphicsMode) withObject:nil waitUntilDone: YES];
 
-	updateScreen();
+	// TODO: Can we return better error codes?
+	return kTransactionSuccess;
 }
 
 void OSystem_IPHONE::updateOutputSurface() {