- Prevented direct reference to the back buffer in many cases (apart from a few, where it's modified directly)

- Added skeleton code for dirty rectangle handling (still unfinished and non-working)
- Added wrapper functions to access the back buffer, which add the appropriate dirty rectangles automatically

svn-id: r35264

12 files changed, 207 insertions, 90 deletions

diff --git a/engines/saga/events.cpp b/engines/saga/events.cpp
index a456e81f96..b42ea97765 100644
--- a/engines/saga/events.cpp
+++ b/engines/saga/events.cpp
@@ -522,7 +522,7 @@ int Events::handleOneShot(Event *event) {
 			rect.bottom = event->param3;
 			rect.left = event->param4;
 			rect.right = event->param5;
-			((Surface *)event->data)->drawRect(rect, event->param);
+			_vm->_gfx->drawRect(rect, event->param);
 			break;
 		case kEventSetFlag:
 			_vm->_render->setFlag(event->param);
diff --git a/engines/saga/font.cpp b/engines/saga/font.cpp
index 1361e310d6..d9d8a4ab8a 100644
--- a/engines/saga/font.cpp
+++ b/engines/saga/font.cpp
@@ -310,7 +310,6 @@ void Font::outFont(const FontStyle &drawFont, const char *text, size_t count, co
 	byte *outputPointer;
 	byte *outputPointer_min;
 	byte *outputPointer_max;
-	Surface *backBuffer = _vm->_gfx->getBackBuffer();
 
 	int row;
 	int rowLimit;
@@ -320,7 +319,7 @@ void Font::outFont(const FontStyle &drawFont, const char *text, size_t count, co
 	int c_bit;
 	int ct;
 
-	if ((point.x > backBuffer->w) || (point.y > backBuffer->h)) {
+	if ((point.x > _vm->_gfx->getBackBufferWidth()) || (point.y > _vm->_gfx->getBackBufferHeight())) {
 		// Output string can't be visible
 		return;
 	}
@@ -373,7 +372,7 @@ void Font::outFont(const FontStyle &drawFont, const char *text, size_t count, co
 
 		// Get length of character in bytes
 		c_byte_len = ((drawFont.fontCharEntry[c_code].width - 1) / 8) + 1;
-		rowLimit = (backBuffer->h < (textPoint.y + drawFont.header.charHeight)) ? backBuffer->h : textPoint.y + drawFont.header.charHeight;
+		rowLimit = (_vm->_gfx->getBackBufferHeight() < (textPoint.y + drawFont.header.charHeight)) ? _vm->_gfx->getBackBufferHeight() : textPoint.y + drawFont.header.charHeight;
 		charRow = 0;
 
 		for (row = textPoint.y; row < rowLimit; row++, charRow++) {
@@ -382,9 +381,9 @@ void Font::outFont(const FontStyle &drawFont, const char *text, size_t count, co
 				continue;
 			}
 
-			outputPointer = (byte *)backBuffer->pixels + (backBuffer->pitch * row) + textPoint.x;
-			outputPointer_min = (byte *)backBuffer->pixels + (backBuffer->pitch * row) + (textPoint.x > 0 ? textPoint.x : 0);
-			outputPointer_max = outputPointer + (backBuffer->pitch - textPoint.x);
+			outputPointer = _vm->_gfx->getBackBufferPixels() + (_vm->_gfx->getBackBufferPitch() * row) + textPoint.x;
+			outputPointer_min = _vm->_gfx->getBackBufferPixels() + (_vm->_gfx->getBackBufferPitch() * row) + (textPoint.x > 0 ? textPoint.x : 0);
+			outputPointer_max = outputPointer + (_vm->_gfx->getBackBufferPitch() - textPoint.x);
 
 			// If character starts off the screen, jump to next character
 			if (outputPointer < outputPointer_min) {
@@ -415,7 +414,6 @@ void Font::textDraw(FontId fontId, const char *text, const Common::Point &point,
 	int textLength;
 	int fitWidth;
 	Common::Point textPoint(point);
-	Surface *backBuffer = _vm->_gfx->getBackBuffer();
 
 	textLength = strlen(text);
 
@@ -431,8 +429,8 @@ void Font::textDraw(FontId fontId, const char *text, const Common::Point &point,
 		textPoint.x = TEXT_CENTERLIMIT;
 	}
 
-	if (textPoint.x > backBuffer->w - TEXT_CENTERLIMIT) {
-		textPoint.x = backBuffer->w - TEXT_CENTERLIMIT;
+	if (textPoint.x > _vm->_gfx->getBackBufferWidth() - TEXT_CENTERLIMIT) {
+		textPoint.x = _vm->_gfx->getBackBufferWidth() - TEXT_CENTERLIMIT;
 	}
 
 	if (textPoint.x < (TEXT_MARGIN * 2)) {
@@ -442,12 +440,12 @@ void Font::textDraw(FontId fontId, const char *text, const Common::Point &point,
 
 	textWidth = getStringWidth(fontId, text, textLength, flags);
 
-	if (textPoint.x < (backBuffer->w / 2)) {
+	if (textPoint.x < (_vm->_gfx->getBackBufferWidth() / 2)) {
 		// Fit to right side
 		fitWidth = (textPoint.x - TEXT_MARGIN) * 2;
 	} else {
 		// Fit to left side
-		fitWidth = ((backBuffer->w - TEXT_MARGIN) - textPoint.x) * 2;
+		fitWidth = ((_vm->_gfx->getBackBufferWidth() - TEXT_MARGIN) - textPoint.x) * 2;
 	}
 
 	if (fitWidth < textWidth) {
diff --git a/engines/saga/gfx.cpp b/engines/saga/gfx.cpp
index 285a33b656..eac1d871ae 100644
--- a/engines/saga/gfx.cpp
+++ b/engines/saga/gfx.cpp
@@ -30,6 +30,7 @@
 #include "saga/interface.h"
 #include "saga/rscfile.h"
 #include "saga/scene.h"
+#include "saga/render.h"
 
 #include "common/system.h"
 #include "graphics/cursorman.h"
@@ -561,4 +562,28 @@ bool hitTestPoly(const Point *points, unsigned int npoints, const Point& test_po
 	return inside_flag;
 }
 
+// This method adds a dirty rectangle automatically
+void Gfx::drawFrame(const Common::Point &p1, const Common::Point &p2, int color) {
+	_backBuffer.drawFrame(p1, p2, color);
+	_vm->_render->addDirtyRect(Common::Rect(p1.x, p1.y, p2.x, p2.y));
+}
+
+// This method adds a dirty rectangle automatically
+void Gfx::drawRect(const Common::Rect &destRect, int color) {
+	_backBuffer.drawRect(destRect, color);
+	_vm->_render->addDirtyRect(destRect);
+}
+
+// This method adds a dirty rectangle automatically
+void Gfx::fillRect(const Common::Rect &destRect, uint32 color) {
+	_backBuffer.fillRect(destRect, color);
+	_vm->_render->addDirtyRect(destRect);
+}
+
+// This method adds a dirty rectangle automatically
+void Gfx::drawRegion(const Common::Rect &destRect, const byte *sourceBuffer) {
+	_backBuffer.blit(destRect, sourceBuffer);
+	_vm->_render->addDirtyRect(destRect);
+}
+
 } // End of namespace Saga
diff --git a/engines/saga/gfx.h b/engines/saga/gfx.h
index 7894dfaff3..6cd5d2469b 100644
--- a/engines/saga/gfx.h
+++ b/engines/saga/gfx.h
@@ -138,9 +138,6 @@ public:
 
 	Gfx(SagaEngine *vm, OSystem *system, int width, int height);
 	~Gfx();
-	Surface *getBackBuffer() {
-		return &_backBuffer;
-	}
 
 	void initPalette();
 	void setPalette(const PalEntry *pal, bool full = false);
@@ -154,6 +151,77 @@ public:
 	void showCursor(bool state);
 	void setCursor(CursorType cursorType = kCursorNormal);
 
+	// Back buffer access methods. These all take care of adding the necessary dirty rectangles
+	// APART FROM setPixelColor() and getBackBufferPixels()
+
+	// This method adds a dirty rectangle automatically
+	void drawFrame(const Common::Point &p1, const Common::Point &p2, int color);
+
+	// This method adds a dirty rectangle automatically
+	void drawRect(const Common::Rect &destRect, int color);
+
+	// This method adds a dirty rectangle automatically
+	void fillRect(const Common::Rect &destRect, uint32 color);
+
+	// This method adds a dirty rectangle automatically
+	void drawRegion(const Common::Rect &destRect, const byte *sourceBuffer);
+
+	// Used for testing
+	void drawPalette() {
+		_backBuffer.drawPalette();
+	}
+
+	// WARNING: This method does not add a dirty rectangle automatically.
+	// Whenever it gets called, the corresponding caller must take care
+	// to add the corresponding dirty rectangle itself
+	void hLine(int x, int y, int x2, uint32 color) {
+		_backBuffer.hLine(x, y, x2, color);
+	}
+
+	// WARNING: This method does not add a dirty rectangle automatically.
+	// Whenever it gets called, the corresponding caller must take care
+	// to add the corresponding dirty rectangle itself
+	void vLine(int x, int y, int y2, uint32 color) {
+		_backBuffer.vLine(x, y, y2, color);
+	}
+
+	// WARNING: This method does not add a dirty rectangle automatically.
+	// Whenever it gets called, the corresponding caller must take care
+	// to add the corresponding dirty rectangle itself
+	void setPixelColor(int x, int y, byte color) {
+		((byte *)_backBuffer.getBasePtr(x, y))[0] = color;
+	}
+
+	// WARNING: This method does not add a dirty rectangle automatically.
+	// Whenever it gets called, the corresponding caller must take care
+	// to add the corresponding dirty rectangle itself
+	void drawPolyLine(Common::Point *points, int count, int color) {
+		_backBuffer.drawPolyLine(points, count, color);
+	}
+
+	// WARNING: This method allows direct modification of the back buffer
+	// Whenever it gets called, the corresponding caller must take care
+	// to add the corresponding dirty rectangle itself
+	byte *getBackBufferPixels() {
+		return (byte *)_backBuffer.pixels;
+	}
+
+	uint16 getBackBufferWidth() {
+		return _backBuffer.w;
+	}
+
+	uint16 getBackBufferHeight() {
+		return _backBuffer.h;
+	}
+
+	uint16 getBackBufferPitch() {
+		return _backBuffer.pitch;
+	}
+
+	void getBackBufferRect(Common::Rect &rect) {
+		_backBuffer.getRect(rect);
+	}
+
 private:
 	Surface _backBuffer;
 	byte _currentPal[PAL_ENTRIES * 4];
diff --git a/engines/saga/interface.cpp b/engines/saga/interface.cpp
index e6c6921784..e18e1654a0 100644
--- a/engines/saga/interface.cpp
+++ b/engines/saga/interface.cpp
@@ -799,7 +799,7 @@ void Interface::draw() {
 	if (_panelMode == kPanelMain || _panelMode == kPanelMap ||
 		(_panelMode == kPanelNull && _vm->getGameId() == GID_IHNM_DEMO)) {
 		_mainPanel.getRect(rect);
-		_vm->_gfx->getBackBuffer()->blit(rect, _mainPanel.image);
+		_vm->_gfx->drawRegion(rect, _mainPanel.image);
 
 		for (int i = 0; i < kVerbTypeIdsMax; i++) {
 			if (_verbTypeToPanelButton[i] != NULL) {
@@ -808,7 +808,7 @@ void Interface::draw() {
 		}
 	} else if (_panelMode == kPanelConverse) {
 		_conversePanel.getRect(rect);
-		_vm->_gfx->getBackBuffer()->blit(rect, _conversePanel.image);
+		_vm->_gfx->drawRegion(rect, _conversePanel.image);
 		converseDisplayTextLines();
 	}
 
@@ -941,10 +941,9 @@ void Interface::drawOption() {
 	Point point;
 	Point sliderPoint;
 	int spritenum = 0;
-	Surface *backBuffer = _vm->_gfx->getBackBuffer();
 
 	_optionPanel.getRect(rect);
-	backBuffer->blit(rect, _optionPanel.image);
+	_vm->_gfx->drawRegion(rect, _optionPanel.image);
 
 	for (int i = 0; i < _optionPanel.buttonsCount; i++) {
 		panelButton = &_optionPanel.buttons[i];
@@ -964,7 +963,7 @@ void Interface::drawOption() {
 
 	if (_optionSaveRectTop.height() > 0) {
 		if (_vm->getGameType() == GType_ITE)
-			backBuffer->drawRect(_optionSaveRectTop, kITEColorDarkGrey);
+			_vm->_gfx->drawRect(_optionSaveRectTop, kITEColorDarkGrey);
 	}
 
 	if (_vm->getGameType() == GType_ITE) {
@@ -978,7 +977,7 @@ void Interface::drawOption() {
 	}
 
 	if (_optionSaveRectBottom.height() > 0) {
-		backBuffer->drawRect(_optionSaveRectBottom, kITEColorDarkGrey);
+		_vm->_gfx->drawRect(_optionSaveRectBottom, kITEColorDarkGrey);
 	}
 
 	_optionPanel.calcPanelButtonRect(_optionSaveFilePanel, rect);
@@ -999,7 +998,7 @@ void Interface::drawOption() {
 		if (idx < _vm->getSaveFilesCount()) {
 			rect2.top = rect.top + j * (fontHeight + 1);
 			rect2.bottom = rect2.top + fontHeight;
-			backBuffer->fillRect(rect2, bgColor);
+			_vm->_gfx->fillRect(rect2, bgColor);
 			text = _vm->getSaveFile(idx)->name;
 			textPoint.x = rect.left + 1;
 			textPoint.y = rect2.top;
@@ -1021,7 +1020,7 @@ void Interface::drawQuit() {
 	if (_vm->getGameType() == GType_ITE)
 		drawButtonBox(rect, kButton, false);
 	else
-		_vm->_gfx->getBackBuffer()->blit(rect, _quitPanel.image);
+		_vm->_gfx->drawRegion(rect, _quitPanel.image);
 
 	for (i = 0; i < _quitPanel.buttonsCount; i++) {
 		panelButton = &_quitPanel.buttons[i];
@@ -1085,7 +1084,7 @@ void Interface::drawLoad() {
 	if (_vm->getGameType() == GType_ITE)
 		drawButtonBox(rect, kButton, false);
 	else
-		_vm->_gfx->getBackBuffer()->blit(rect, _loadPanel.image);
+		_vm->_gfx->drawRegion(rect, _loadPanel.image);
 
 	for (i = 0; i < _loadPanel.buttonsCount; i++) {
 		panelButton = &_loadPanel.buttons[i];
@@ -1266,7 +1265,6 @@ void Interface::drawTextInput(InterfacePanel *panel, PanelButton *panelButton) {
 	char ch[2];
 	int fgColor;
 	uint i;
-	Surface *backBuffer = _vm->_gfx->getBackBuffer();
 
 	ch[1] = 0;
 	panel->calcPanelButtonRect(panelButton, rect);
@@ -1280,7 +1278,7 @@ void Interface::drawTextInput(InterfacePanel *panel, PanelButton *panelButton) {
 		rect.setWidth(_vm->_font->getStringWidth(kKnownFontSmall, ch, 0, kFontNormal));
 		if ((i == _textInputPos) && _textInput) {
 			fgColor = _vm->KnownColor2ColorId(kKnownColorBlack);
-			backBuffer->fillRect(rect, _vm->KnownColor2ColorId(kKnownColorWhite));
+			_vm->_gfx->fillRect(rect, _vm->KnownColor2ColorId(kKnownColorWhite));
 		} else {
 			fgColor = _vm->KnownColor2ColorId(kKnownColorWhite);
 		}
@@ -1293,7 +1291,7 @@ void Interface::drawTextInput(InterfacePanel *panel, PanelButton *panelButton) {
 	if (_textInput && (_textInputPos >= i)) {
 		ch[0] = ' ';
 		rect.setWidth(_vm->_font->getStringWidth(kKnownFontSmall, ch, 0, kFontNormal));
-		backBuffer->fillRect(rect, _vm->KnownColor2ColorId(kKnownColorWhite));
+		_vm->_gfx->fillRect(rect, _vm->KnownColor2ColorId(kKnownColorWhite));
 	}
 }
 
@@ -1306,7 +1304,7 @@ void Interface::drawSave() {
 	if (_vm->getGameType() == GType_ITE)
 		drawButtonBox(rect, kButton, false);
 	else
-		_vm->_gfx->getBackBuffer()->blit(rect, _savePanel.image);
+		_vm->_gfx->drawRegion(rect, _savePanel.image);
 
 	for (i = 0; i < _savePanel.buttonsCount; i++) {
 		panelButton = &_savePanel.buttons[i];
@@ -1882,7 +1880,7 @@ void Interface::drawStatusBar() {
 	rect.right = rect.left + _vm->getDisplayWidth();
 	rect.bottom = rect.top + _vm->getDisplayInfo().statusHeight;
 
-	_vm->_gfx->getBackBuffer()->drawRect(rect, _vm->getDisplayInfo().statusBGColor - offset);
+	_vm->_gfx->drawRect(rect, _vm->getDisplayInfo().statusBGColor - offset);
 
 	stringWidth = _vm->_font->getStringWidth(kKnownFontSmall, _statusText, 0, kFontNormal);
 
@@ -2097,7 +2095,6 @@ void Interface::drawInventory() {
 	Rect rect;
 	int ci = _inventoryStart;
 	ObjectData *obj;
-	Surface *backBuffer = _vm->_gfx->getBackBuffer();
 
 	if (_inventoryStart != 0) {
 		drawPanelButtonArrow(&_mainPanel, _inventoryUpButton);
@@ -2113,9 +2110,9 @@ void Interface::drawInventory() {
 		_mainPanel.calcPanelButtonRect(&_mainPanel.buttons[i], rect);
 
 		if (_vm->getGameType() == GType_ITE)
-			backBuffer->drawRect(rect, kITEColorDarkGrey);
+			_vm->_gfx->drawRect(rect, kITEColorDarkGrey);
 		else
-			backBuffer->drawRect(rect, _vm->KnownColor2ColorId(kKnownColorBlack));
+			_vm->_gfx->drawRect(rect, _vm->KnownColor2ColorId(kKnownColorBlack));
 
 		if (ci < _inventoryCount) {
 			obj = _vm->_actor->getObj(_inventory[ci]);
@@ -2142,7 +2139,6 @@ void Interface::drawButtonBox(const Rect& rect, ButtonKind kind, bool down) {
 	byte fillColor;
 	byte solidColor;
 	byte odl, our, idl, iur;
-	Surface *backBuffer = _vm->_gfx->getBackBuffer();
 
 	switch (kind ) {
 		case kSlider:
@@ -2190,14 +2186,11 @@ void Interface::drawButtonBox(const Rect& rect, ButtonKind kind, bool down) {
 	int xe = rect.right - 1;
 	int ye = rect.bottom - 1;
 
-	((byte *)backBuffer->getBasePtr(x, y))[0] = cornerColor;
-	((byte *)backBuffer->getBasePtr(x, ye))[0] = cornerColor;
-	((byte *)backBuffer->getBasePtr(xe, y))[0] = cornerColor;
-	((byte *)backBuffer->getBasePtr(xe, ye))[0] = cornerColor;
-	backBuffer->hLine(x + 1, y, x + w - 2, frameColor);
-	backBuffer->hLine(x + 1, ye, x + w - 2, frameColor);
-	backBuffer->vLine(x, y + 1, y + h - 2, frameColor);
-	backBuffer->vLine(xe, y + 1, y + h - 2, frameColor);
+	_vm->_gfx->drawRect(Common::Rect(x, y, x + w, y + h), frameColor);
+	_vm->_gfx->setPixelColor(x, y, cornerColor);
+	_vm->_gfx->setPixelColor(x, ye, cornerColor);
+	_vm->_gfx->setPixelColor(xe, y, cornerColor);
+	_vm->_gfx->setPixelColor(xe, ye, cornerColor);
 
 	x++;
 	y++;
@@ -2205,10 +2198,11 @@ void Interface::drawButtonBox(const Rect& rect, ButtonKind kind, bool down) {
 	ye--;
 	w -= 2;
 	h -= 2;
-	backBuffer->vLine(x, y, y + h - 1, odl);
-	backBuffer->hLine(x, ye, x + w - 1, odl);
-	backBuffer->vLine(xe, y, y + h - 2, our);
-	backBuffer->hLine(x + 1, y, x + 1 + w - 2, our);
+	// drawRect() above added a dirty rectangle automatically for these
+	_vm->_gfx->vLine(x, y, y + h - 1, odl);
+	_vm->_gfx->hLine(x, ye, x + w - 1, odl);
+	_vm->_gfx->vLine(xe, y, y + h - 2, our);
+	_vm->_gfx->hLine(x + 1, y, x + 1 + w - 2, our);
 
 	x++;
 	y++;
@@ -2216,18 +2210,19 @@ void Interface::drawButtonBox(const Rect& rect, ButtonKind kind, bool down) {
 	ye--;
 	w -= 2;
 	h -= 2;
-	((byte *)backBuffer->getBasePtr(x, y))[0] = fillColor;
-	((byte *)backBuffer->getBasePtr(xe, ye))[0] = fillColor;
-	backBuffer->vLine(x, y + 1, y + 1 + h - 2, idl);
-	backBuffer->hLine(x + 1, ye, x + 1 + w - 2, idl);
-	backBuffer->vLine(xe, y, y + h - 2, iur);
-	backBuffer->hLine(x + 1, y, x + 1 + w - 2, iur);
+	// drawRect() above added a dirty rectangle automatically for these
+	_vm->_gfx->setPixelColor(x, y, fillColor);
+	_vm->_gfx->setPixelColor(xe, ye, fillColor);
+	_vm->_gfx->vLine(x, y + 1, y + 1 + h - 2, idl);
+	_vm->_gfx->hLine(x + 1, ye, x + 1 + w - 2, idl);
+	_vm->_gfx->vLine(xe, y, y + h - 2, iur);
+	_vm->_gfx->hLine(x + 1, y, x + 1 + w - 2, iur);
 
 	x++; y++;
 	w -= 2; h -= 2;
 
 	Common::Rect fill(x, y, x + w, y + h);
-	backBuffer->fillRect(fill, solidColor);
+	_vm->_gfx->fillRect(fill, solidColor);
 }
 
 static const int readingSpeeds[] = { kTextClick, kTextSlow, kTextMid, kTextFast };
@@ -2519,7 +2514,6 @@ void Interface::converseDisplayTextLines() {
 	};
 	Rect rect(8, _vm->getDisplayInfo().converseTextLines * _vm->getDisplayInfo().converseTextHeight);
 	Point textPoint;
-	Surface *backBuffer = _vm->_gfx->getBackBuffer();
 
 	assert(_conversePanel.buttonsCount >= 6);
 
@@ -2536,9 +2530,9 @@ void Interface::converseDisplayTextLines() {
 		_conversePanel.y + _conversePanel.buttons[0].yOffset);
 
 	if (_vm->getGameType() == GType_ITE)
-		backBuffer->drawRect(rect, kITEColorDarkGrey);	//fill bullet place
+		_vm->_gfx->drawRect(rect, kITEColorDarkGrey);	//fill bullet place
 	else
-		backBuffer->drawRect(rect, _vm->KnownColor2ColorId(kKnownColorBlack));	//fill bullet place
+		_vm->_gfx->drawRect(rect, _vm->KnownColor2ColorId(kKnownColorBlack));	//fill bullet place
 
 	for (int i = 0; i < _vm->getDisplayInfo().converseTextLines; i++) {
 		relPos = _converseStartPos + i;
@@ -2567,7 +2561,7 @@ void Interface::converseDisplayTextLines() {
 
 		_conversePanel.calcPanelButtonRect(&_conversePanel.buttons[i], rect);
 		rect.left += 8;
-		backBuffer->drawRect(rect, backgnd);
+		_vm->_gfx->drawRect(rect, backgnd);
 
 		str = _converseText[relPos].text;
 
@@ -2743,7 +2737,7 @@ void Interface::mapPanelShow() {
 	rect.setWidth(imageWidth);
 	rect.setHeight(imageHeight);
 
-	_vm->_gfx->getBackBuffer()->blit(rect, image);
+	_vm->_gfx->drawRegion(rect, image);
 
 	// Evil Evil
 	for (i = 0; i < 6 ; i++) {
@@ -2847,7 +2841,7 @@ void Interface::keyBoss() {
 		cPal[i].blue = 128;
 	}
 
-	_vm->_gfx->getBackBuffer()->blit(rect, image);
+	_vm->_gfx->drawRegion(rect, image);
 
 	_vm->_gfx->setPalette(cPal);
 
diff --git a/engines/saga/isomap.cpp b/engines/saga/isomap.cpp
index 6a4b5110dd..dd481f00e5 100644
--- a/engines/saga/isomap.cpp
+++ b/engines/saga/isomap.cpp
@@ -378,7 +378,7 @@ int16 IsoMap::findMulti(int16 tileIndex, int16 absU, int16 absV, int16 absH) {
 
 void IsoMap::draw() {
 	_tileClip = _vm->_scene->getSceneClip();
-	_vm->_gfx->getBackBuffer()->drawRect(_tileClip, 0);
+	_vm->_gfx->drawRegion(_tileClip, 0);
 	drawTiles(NULL);
 }
 
@@ -708,7 +708,6 @@ void IsoMap::drawTile(uint16 tileIndex, const Point &point, const Location *loca
 	int row, col, count, lowBound;
 	int bgRunCount;
 	int fgRunCount;
-	Surface *backBuffer = _vm->_gfx->getBackBuffer();
 
 	if (tileIndex >= _tilesCount) {
 		error("IsoMap::drawTile wrong tileIndex");
@@ -832,7 +831,7 @@ void IsoMap::drawTile(uint16 tileIndex, const Point &point, const Location *loca
 	for (row = drawPoint.y; row < lowBound; row++) {
 		widthCount = 0;
 		if (row >= _tileClip.top) {
-			drawPointer = (byte *)backBuffer->pixels + drawPoint.x + (row * backBuffer->pitch);
+			drawPointer = _vm->_gfx->getBackBufferPixels() + drawPoint.x + (row * _vm->_gfx->getBackBufferPitch());
 			col = drawPoint.x;
 			for (;;) {
 				bgRunCount = *readPointer++;
@@ -852,8 +851,8 @@ void IsoMap::drawTile(uint16 tileIndex, const Point &point, const Location *loca
 					col++;
 				}
 				while ((col < _tileClip.right) && (count < fgRunCount)) {
-					assert((byte *)backBuffer->pixels <= (byte *)(drawPointer + count));
-					assert((byte *)((byte *)backBuffer->pixels + (_vm->getDisplayWidth() *
+					assert(_vm->_gfx->getBackBufferPixels() <= (byte *)(drawPointer + count));
+					assert((_vm->_gfx->getBackBufferPixels() + (_vm->getDisplayWidth() *
 								 _vm->getDisplayHeight())) > (byte *)(drawPointer + count));
 					drawPointer[count] = readPointer[count];
 					count++;
diff --git a/engines/saga/objectmap.cpp b/engines/saga/objectmap.cpp
index 17256a67d9..d10c4ffaa7 100644
--- a/engines/saga/objectmap.cpp
+++ b/engines/saga/objectmap.cpp
@@ -149,7 +149,6 @@ void HitZone::draw(SagaEngine *vm, int color) {
 	Point *points;
 	Point specialPoint1;
 	Point specialPoint2;
-	Surface *backBuffer = vm->_gfx->getBackBuffer();
 
 	for (i = 0; i < _clickAreasCount; i++) {
 		clickArea = &_clickAreas[i];
@@ -168,11 +167,11 @@ void HitZone::draw(SagaEngine *vm, int color) {
 
 		if (pointsCount == 2) {
 			// 2 points represent a box
-			backBuffer->drawFrame(points[0], points[1], color);
+			vm->_gfx->drawFrame(points[0], points[1], color);
 		} else {
 			if (pointsCount > 2) {
 				// Otherwise draw a polyline
-				backBuffer->drawPolyLine(points, pointsCount, color);
+				vm->_gfx->drawPolyLine(points, pointsCount, color);
 			}
 		}
 		if (vm->_scene->getFlags() & kSceneFlagISO) {
@@ -186,7 +185,7 @@ void HitZone::draw(SagaEngine *vm, int color) {
 		specialPoint1.y--;
 		specialPoint2.x++;
 		specialPoint2.y++;
-		backBuffer->drawFrame(specialPoint1, specialPoint2, color);
+		vm->_gfx->drawFrame(specialPoint1, specialPoint2, color);
 	}
 }
 #endif
diff --git a/engines/saga/render.cpp b/engines/saga/render.cpp
index fa84188a78..e78e6f9947 100644
--- a/engines/saga/render.cpp
+++ b/engines/saga/render.cpp
@@ -77,18 +77,18 @@ bool Render::initialized() {
 }
 
 void Render::drawScene() {
-	Surface *backBufferSurface;
 	Point mousePoint;
 	Point textPoint;
 	int curMode = _vm->_interface->getMode();
 	assert(_initialized);
 
+	// TODO: Remove this
+	_fullRefresh = true;
+
 #ifdef SAGA_DEBUG
 	_renderedFrameCount++;
 #endif
 
-	backBufferSurface = _vm->_gfx->getBackBuffer();
-
 	// Get mouse coordinates
 	mousePoint = _vm->mousePos();
 
@@ -165,7 +165,7 @@ void Render::drawScene() {
 	if (_flags & RF_SHOW_FPS) {
 		char txtBuffer[20];
 		sprintf(txtBuffer, "%d", _fps);
-		textPoint.x = backBufferSurface->w - _vm->_font->getStringWidth(kKnownFontSmall, txtBuffer, 0, kFontOutline);
+		textPoint.x = _vm->_gfx->getBackBufferWidth() - _vm->_font->getStringWidth(kKnownFontSmall, txtBuffer, 0, kFontOutline);
 		textPoint.y = 2;
 
 		_vm->_font->textDraw(kKnownFontSmall, txtBuffer, textPoint, kITEColorBrightWhite, kITEColorBlack, kFontOutline);
@@ -175,7 +175,7 @@ void Render::drawScene() {
 	// Display "paused game" message, if applicable
 	if (_flags & RF_RENDERPAUSE) {
 		const char *pauseString = (_vm->getGameType() == GType_ITE) ? pauseStringITE : pauseStringIHNM;
-		textPoint.x = (backBufferSurface->w - _vm->_font->getStringWidth(kKnownFontPause, pauseString, 0, kFontOutline)) / 2;
+		textPoint.x = (_vm->_gfx->getBackBufferWidth() - _vm->_font->getStringWidth(kKnownFontPause, pauseString, 0, kFontOutline)) / 2;
 		textPoint.y = 90;
 
 		_vm->_font->textDraw(kKnownFontPause, pauseString, textPoint, 
@@ -195,16 +195,32 @@ void Render::drawScene() {
 
 	// Display palette test, if applicable
 	if (_flags & RF_PALETTE_TEST) {
-		backBufferSurface->drawPalette();
+		_vm->_gfx->drawPalette();
 	}
 #endif
 
-	_system->copyRectToScreen((byte *)backBufferSurface->pixels, backBufferSurface->w, 0, 0,
-							  backBufferSurface->w, backBufferSurface->h);
+	drawDirtyRects();
 
 	_system->updateScreen();
 }
 
+void Render::drawDirtyRects() {
+	if (_fullRefresh) {
+		_system->copyRectToScreen(_vm->_gfx->getBackBufferPixels(), _vm->_gfx->getBackBufferWidth(), 0, 0,
+								  _vm->_gfx->getBackBufferWidth(), _vm->_gfx->getBackBufferHeight());
+	} else {
+
+		// TODO: check if dirty rectangles are intersecting or contained within each other
+
+ 	 	Common::List<Common::Rect>::const_iterator it;
+ 	 	for (it = _dirtyRects.begin(); it != _dirtyRects.end(); ++it) {
+			g_system->copyRectToScreen(_vm->_gfx->getBackBufferPixels(), it->width(), it->left, it->top, it->width(), it->height());
+		}
+	}
+
+	_dirtyRects.clear();
+}
+
 #ifdef SAGA_DEBUG
 void Render::fpsTimerCallback(void *refCon) {
 	((Render *)refCon)->fpsTimer();
diff --git a/engines/saga/render.h b/engines/saga/render.h
index fe4ce7f890..772bbca1a6 100644
--- a/engines/saga/render.h
+++ b/engines/saga/render.h
@@ -29,6 +29,8 @@
 #define SAGA_RENDER_H
 
 #include "saga/sprite.h"
+#include "saga/gfx.h"
+#include "common/list.h"
 
 namespace Saga {
 
@@ -77,6 +79,24 @@ public:
 		return &_backGroundSurface;
 	}
 
+	void addDirtyRect(Common::Rect rect) {
+		_dirtyRects.push_back(rect);
+	}
+
+	void clearDirtyRects() {
+		_dirtyRects.clear();
+	}
+
+	void setFullRefresh(bool flag) {
+		_fullRefresh = flag;
+	}
+
+	bool isFullRefresh() {
+		return _fullRefresh;
+	}
+
+	void drawDirtyRects();
+
 private:
 #ifdef SAGA_DEBUG
 	static void fpsTimerCallback(void *refCon);
@@ -88,6 +108,8 @@ private:
 	SagaEngine *_vm;
 	OSystem *_system;
 	bool _initialized;
+	Common::List<Common::Rect> _dirtyRects;
+	bool _fullRefresh;
 
 	// Module data
 	Surface _backGroundSurface;
diff --git a/engines/saga/scene.cpp b/engines/saga/scene.cpp
index de7ad727de..5a7a7446e1 100644
--- a/engines/saga/scene.cpp
+++ b/engines/saga/scene.cpp
@@ -468,7 +468,7 @@ void Scene::changeScene(int16 sceneNumber, int actorsEntrance, SceneTransitionTy
 					colors = pal;
 					rect.setWidth(bbmBuffer.w);
 					rect.setHeight(bbmBuffer.h);
-					_vm->_gfx->getBackBuffer()->blit(rect, (const byte*)bbmBuffer.pixels);
+					_vm->_gfx->drawRegion(rect, (const byte*)bbmBuffer.pixels);
 					for (int j = 0; j < PAL_ENTRIES; j++) {
 						cPal[j].red = *pal++;
 						cPal[j].green = *pal++;
@@ -1151,7 +1151,7 @@ void Scene::draw() {
 		Rect rect;
 		_vm->_render->getBackGroundSurface()->getRect(rect);
 		rect.bottom = (_sceneClip.bottom < rect.bottom) ? getHeight() : rect.bottom;
-		_vm->_gfx->getBackBuffer()->blit(rect, (const byte *)_vm->_render->getBackGroundSurface()->pixels);
+		_vm->_gfx->drawRegion(rect, (const byte *)_vm->_render->getBackGroundSurface()->pixels);
 	}
 }
 
@@ -1181,8 +1181,8 @@ void Scene::endScene() {
 		_vm->_scene->getBGInfo(bgInfo);
 		_vm->_render->getBackGroundSurface()->blit(bgInfo.bounds, bgInfo.buffer);
 	} else {
-		_vm->_gfx->getBackBuffer()->getRect(rect);
-		_vm->_render->getBackGroundSurface()->blit(rect, (const byte *)_vm->_gfx->getBackBuffer()->pixels);
+		_vm->_gfx->getBackBufferRect(rect);
+		_vm->_render->getBackGroundSurface()->blit(rect, (const byte *)_vm->_gfx->getBackBufferPixels());
 	}
 
 	// Free scene background
diff --git a/engines/saga/sfuncs.cpp b/engines/saga/sfuncs.cpp
index c2d7096153..54cded5d25 100644
--- a/engines/saga/sfuncs.cpp
+++ b/engines/saga/sfuncs.cpp
@@ -1171,7 +1171,6 @@ void Script::sfSimulSpeech2(SCRIPTFUNC_PARAMS) {
 // Param1: string rid
 void Script::sfPlacard(SCRIPTFUNC_PARAMS) {
 	int stringId = thread->pop();
-	Surface *backBuffer = _vm->_gfx->getBackBuffer();
 	static PalEntry cur_pal[PAL_ENTRIES];
 	PalEntry *pal;
 	Event event;
@@ -1216,7 +1215,6 @@ void Script::sfPlacard(SCRIPTFUNC_PARAMS) {
 	event.type = kEvTOneshot;
 	event.code = kGraphicsEvent;
 	event.op = kEventFillRect;
-	event.data = backBuffer;
 	event.param = 138;
 	event.param2 = 0;
 	event.param3 = _vm->_scene->getHeight();
diff --git a/engines/saga/sprite.cpp b/engines/saga/sprite.cpp
index 2723ce7d7f..200b0af206 100644
--- a/engines/saga/sprite.cpp
+++ b/engines/saga/sprite.cpp
@@ -218,9 +218,8 @@ void Sprite::drawClip(const Rect &clipRect, const Point &spritePointer, int widt
 	int i, j, jo, io;
 	byte *bufRowPointer;
 	const byte *srcRowPointer;
-	Surface *backBuffer = _vm->_gfx->getBackBuffer();
 
-	bufRowPointer = (byte *)backBuffer->pixels + backBuffer->pitch * spritePointer.y;
+	bufRowPointer = _vm->_gfx->getBackBufferPixels() + _vm->_gfx->getBackBufferPitch() * spritePointer.y;
 	srcRowPointer = spriteBuffer;
 
 	clipWidth = CLIP(width, 0, clipRect.right - spritePointer.x);
@@ -233,14 +232,14 @@ void Sprite::drawClip(const Rect &clipRect, const Point &spritePointer, int widt
 	}
 	if (spritePointer.y < clipRect.top) {
 		io = clipRect.top - spritePointer.y;
-		bufRowPointer += backBuffer->pitch * io;
+		bufRowPointer += _vm->_gfx->getBackBufferPitch() * io;
 		srcRowPointer += width * io;
 	}
 
 	for (i = io; i < clipHeight; i++) {
 		for (j = jo; j < clipWidth; j++) {
-			assert((byte *)backBuffer->pixels <= (byte *)(bufRowPointer + j + spritePointer.x));
-			assert(((byte *)backBuffer->pixels + (_vm->getDisplayWidth() *
+			assert(_vm->_gfx->getBackBufferPixels() <= (byte *)(bufRowPointer + j + spritePointer.x));
+			assert((_vm->_gfx->getBackBufferPixels() + (_vm->getDisplayWidth() *
 				 _vm->getDisplayHeight())) > (byte *)(bufRowPointer + j + spritePointer.x));
 			assert((const byte *)spriteBuffer <= (const byte *)(srcRowPointer + j));
 			assert(((const byte *)spriteBuffer + (width * height)) > (const byte *)(srcRowPointer + j));
@@ -249,7 +248,7 @@ void Sprite::drawClip(const Rect &clipRect, const Point &spritePointer, int widt
 				*(bufRowPointer + j + spritePointer.x) = *(srcRowPointer + j);
 			}
 		}
-		bufRowPointer += backBuffer->pitch;
+		bufRowPointer += _vm->_gfx->getBackBufferPitch();
 		srcRowPointer += width;
 	}
 }
@@ -333,7 +332,6 @@ void Sprite::drawOccluded(const Rect &clipRect, SpriteList &spriteList, int spri
 	int height = 0;
 	int xAlign = 0;
 	int yAlign = 0;
-	Surface *backBuffer = _vm->_gfx->getBackBuffer();
 
 	ClipData clipData;
 
@@ -371,7 +369,7 @@ void Sprite::drawOccluded(const Rect &clipRect, SpriteList &spriteList, int spri
 	// Finally, draw the occluded sprite
 
 	sourceRowPointer = spriteBuffer + clipData.drawSource.x + (clipData.drawSource.y * width);
-	destRowPointer = (byte *)backBuffer->pixels + clipData.drawDest.x + (clipData.drawDest.y * backBuffer->pitch);
+	destRowPointer = _vm->_gfx->getBackBufferPixels() + clipData.drawDest.x + (clipData.drawDest.y * _vm->_gfx->getBackBufferPitch());
 	maskRowPointer = maskBuffer + clipData.drawDest.x + (clipData.drawDest.y * maskWidth);
 
 	for (y = 0; y < clipData.drawHeight; y++) {
@@ -389,7 +387,7 @@ void Sprite::drawOccluded(const Rect &clipRect, SpriteList &spriteList, int spri
 			destPointer++;
 			maskPointer++;
 		}
-		destRowPointer += backBuffer->pitch;
+		destRowPointer += _vm->_gfx->getBackBufferPitch();
 		maskRowPointer += maskWidth;
 		sourceRowPointer += width;
 	}