3 files changed, 21 insertions, 5 deletions

diff --git a/engines/sci/gui/gui_picture.cpp b/engines/sci/gui/gui_picture.cpp
index d3effcd917..d8fa63954d 100644
--- a/engines/sci/gui/gui_picture.cpp
+++ b/engines/sci/gui/gui_picture.cpp
@@ -498,7 +498,7 @@ void SciGuiPicture::drawVectorData(byte *data, int dataSize) {
 			_priority = pic_priority;
 			// Dithering EGA pictures
 			if (isEGA) {
-				_screen->dither();
+				_screen->dither(_addToFlag);
 			}
 			return;
 		default:
diff --git a/engines/sci/gui/gui_screen.cpp b/engines/sci/gui/gui_screen.cpp
index 26a81ef833..0e0a1ed170 100644
--- a/engines/sci/gui/gui_screen.cpp
+++ b/engines/sci/gui/gui_screen.cpp
@@ -216,7 +216,7 @@ void SciGuiScreen::setPalette(GuiPalette*pal) {
 }
 
 // Currently not really done, its supposed to be possible to only dither _visualScreen
-void SciGuiScreen::dither() {
+void SciGuiScreen::dither(bool addToFlag) {
 	int y, x;
 	byte color;
 	byte *screenPtr = _visualScreen;
@@ -236,12 +236,16 @@ void SciGuiScreen::dither() {
 			}
 		}
 	} else {
+		if (!addToFlag)
+			memset(&_unditherMemorial, 0, sizeof(_unditherMemorial));
 		// Do dithering on visual screen and put decoded but undithered byte onto display-screen
 		for (y = 0; y < _height; y++) {
 			for (x = 0; x < _width; x++) {
 				color = *screenPtr;
 				if (color & 0xF0) {
 					color ^= color << 4;
+					// remember dither combination for cel-undithering
+					_unditherMemorial[color]++;
 					// if decoded color wants do dither with black on left side, we turn it around
 					//  otherwise the normal ega color would get used for display
 					if (color & 0xF0) {
@@ -262,6 +266,13 @@ void SciGuiScreen::unditherSetState(bool flag) {
 	_unditherState = flag;
 }
 
+int16 *SciGuiScreen::unditherGetMemorial() {
+	if (_unditherState)
+		return (int16 *)&_unditherMemorial;
+	else
+		return NULL;
+}
+
 void SciGuiScreen::debugShowMap(int mapNo) {
 	switch (mapNo) {
 	case 0:
diff --git a/engines/sci/gui/gui_screen.h b/engines/sci/gui/gui_screen.h
index c9af0a6ff8..60b49ae351 100644
--- a/engines/sci/gui/gui_screen.h
+++ b/engines/sci/gui/gui_screen.h
@@ -39,6 +39,8 @@ namespace Sci {
 #define SCI_SCREEN_MASK_ALL      SCI_SCREEN_MASK_VISUAL|SCI_SCREEN_MASK_PRIORITY|SCI_SCREEN_MASK_CONTROL
 #define SCI_SCREEN_MASK_DITHERED 128
 
+#define SCI_SCREEN_UNDITHERMEMORIAL_SIZE 256
+
 class SciGuiScreen {
 public:
 	SciGuiScreen(int16 width = 320, int16 height = 200, int16 scaleFactor = 1);
@@ -59,8 +61,9 @@ public:
 
 	void setPalette(GuiPalette*pal);
 
-	void dither();
+	void dither(bool addToFlag);
 	void unditherSetState(bool flag);
+	int16 *unditherGetMemorial();
 
 	void debugShowMap(int mapNo);
 
@@ -73,8 +76,6 @@ public:
 
 	int _picNotValid; // possible values 0, 1 and 2
 
-	bool _unditherState;
-
 private:
 	void restoreBitsScreen(Common::Rect rect, byte *&memoryPtr, byte *screen);
 	void saveBitsScreen(Common::Rect rect, byte *screen, byte *&memoryPtr);
@@ -82,6 +83,9 @@ private:
 	uint16 _baseTable[SCI_SCREEN_MAXHEIGHT];
 	uint16 _baseDisplayTable[SCI_SCREEN_MAXHEIGHT];
 
+	bool _unditherState;
+	int16 _unditherMemorial[SCI_SCREEN_UNDITHERMEMORIAL_SIZE];
+
 public:	// HACK. TODO: make private
 	// these screens have the real resolution of the game engine (320x200 for SCI0/SCI1/SCI11 games, 640x480 for SCI2 games)
 	//  SCI0 games will be dithered in here at any time
@@ -92,6 +96,7 @@ public:	// HACK. TODO: make private
 	// this screen is the one that is actually displayed to the user. It may be 640x480 for japanese SCI1 games
 	//  SCI0 games may be undithered in here. Only read from this buffer for Save/ShowBits usage.
 	byte *_displayScreen;
+private:
 
 	// this is a pointer to the currently active screen (changing it only required for debug purposes)
 	byte *_activeScreen;