PsychError SCREENOpenWindow(void) 

{
    int					screenNumber, numWindowBuffers, stereomode, multiSample, imagingmode;
    PsychRectType 			rect;
    PsychColorType			color;
    PsychColorModeType  		mode; 
    boolean				isArgThere, settingsMade, didWindowOpen;
    PsychScreenSettingsType		screenSettings;
    PsychWindowRecordType		*windowRecord;
    double dVals[4];
    PsychDepthType		specifiedDepth, possibleDepths, currentDepth, useDepth;
	int dummy1;
	double dummy2, dummy3, dummy4;
	Boolean EmulateOldPTB = PsychPrefStateGet_EmulateOldPTB();
    
	//just for debugging
    //if (PSYCH_DEBUG == PSYCH_ON) printf("Entering SCREENOpen\n");

    //all sub functions should have these two lines
    PsychPushHelp(useString, synopsisString, seeAlsoString);
    if(PsychIsGiveHelp()){PsychGiveHelp();return(PsychError_none);};

    //cap the number of inputs
    PsychErrorExit(PsychCapNumInputArgs(8));   //The maximum number of inputs
    PsychErrorExit(PsychCapNumOutputArgs(2));  //The maximum number of outputs

    //get the screen number from the windowPtrOrScreenNumber.  This also checks to make sure that the specified screen exists.  
    PsychCopyInScreenNumberArg(kPsychUseDefaultArgPosition, TRUE, &screenNumber);
    if(screenNumber==-1)
        PsychErrorExitMsg(PsychError_user, "The specified offscreen window has no ancestral screen."); 

    /*
      The depth checking is ugly because of this stupid depth structure stuff.  
      Instead get a descriptor of the current video settings, change the depth field,
      and pass it to a validate function wich searches a list of valid video modes for the display.
      There seems to be no point in checking the depths alone because the legality of a particular
      depth depends on the other settings specified below.  Its probably best to wait until we have
      digested all settings and then test the full mode, declarin an invalid
      mode and not an invalid pixel size.  We could notice when the depth alone is specified 
      and in that case issue an invalid depth value.
     */  

    //find the PixelSize first because the color specifier depends on the screen depth.  
    PsychInitDepthStruct(&currentDepth);  //get the current depth
    PsychGetScreenDepth(screenNumber, &currentDepth);
    PsychInitDepthStruct(&possibleDepths); //get the possible depths
    PsychGetScreenDepths(screenNumber, &possibleDepths);

    #if PSYCH_SYSTEM == PSYCH_OSX || PSYCH_SYSTEM == PSYCH_WINDOWS
       // MK Experimental Hack: Add the special depth values 30, 64 and 128 to the depth struct. This allows for
       // 10 bpc color buffers and 16 bpc, 32 bpc floating point color buffers on the latest ATI
       // and NVidia hardware. Unfortunately at this point of the init sequence, we are not able
       // to check if these formats are supported by the hardware. Ugly ugly ugly...
       PsychAddValueToDepthStruct(30, &possibleDepths);
       PsychAddValueToDepthStruct(64, &possibleDepths);
       PsychAddValueToDepthStruct(128, &possibleDepths);
    #endif

    PsychInitDepthStruct(&specifiedDepth); //get the requested depth and validate it.  
    isArgThere = PsychCopyInSingleDepthArg(4, FALSE, &specifiedDepth);

    PsychInitDepthStruct(&useDepth);
    if(isArgThere){ //if the argument is there check that the screen supports it...
        if(!PsychIsMemberDepthStruct(&specifiedDepth, &possibleDepths))
            PsychErrorExit(PsychError_invalidDepthArg);
        else
            PsychCopyDepthStruct(&useDepth, &specifiedDepth);
    }else //otherwise use the default
        PsychCopyDepthStruct(&useDepth, &currentDepth);

    //find the rect.
    PsychGetScreenRect(screenNumber, rect); 	//get the rect describing the screen bounds.  This is the default Rect.  

    // Override it with a user supplied rect, if one was supplied:
    isArgThere=PsychCopyInRectArg(kPsychUseDefaultArgPosition, FALSE, rect );
    if (IsPsychRectEmpty(rect)) PsychErrorExitMsg(PsychError_user, "OpenWindow called with invalid (empty) rect argument.");

    //find the number of specified buffers. 

    //OS X:	The number of backbuffers is not a property of the display mode but an attribute of the pixel format.
    //		Therefore the value is held by a window record and not a screen record.    

    numWindowBuffers=2;	
    PsychCopyInIntegerArg(5,FALSE,&numWindowBuffers);
    if(numWindowBuffers < 1 || numWindowBuffers > kPsychMaxNumberWindowBuffers) PsychErrorExit(PsychError_invalidNumberBuffersArg);

    // MK: Check for optional spec of stereoscopic display: 0 (the default) = monoscopic viewing.
    // 1 == Stereo output via OpenGL built-in stereo facilities: This will drive any kind of
    // stereo display hardware that is directly supported by MacOS-X.
    // 2/3 == Stereo output via compressed frame output: Only one backbuffer is used for both
    // views: The left view image is put into the top-half of the screen, the right view image
    // is put into the bottom half of the screen. External hardware demangles this combi-image
    // again into two separate images. CrystalEyes seems to be able to do this. One looses half
    // of the vertical resolution, but potentially gains refresh rate...
    // Future PTB version may include different stereo algorithms with an id > 1, e.g., 

    // anaglyph stereo, interlaced stereo, ...

    stereomode=0;
    PsychCopyInIntegerArg(6,FALSE,&stereomode);
    if(stereomode < 0 || stereomode > 9) PsychErrorExitMsg(PsychError_user, "Invalid stereomode provided (Valid between 0 and 9).");
	if (stereomode!=0 && EmulateOldPTB) PsychErrorExitMsg(PsychError_user, "Sorry, stereo display functions are not supported in OS-9 PTB emulation mode.");

    multiSample=0;
    PsychCopyInIntegerArg(7,FALSE,&multiSample);
    if(multiSample < 0) PsychErrorExitMsg(PsychError_user, "Invalid multisample value provided (Valid are positive numbers >= 0).");
	if (multiSample!=0 && EmulateOldPTB) PsychErrorExitMsg(PsychError_user, "Sorry, anti-aliasing functions are not supported in OS-9 PTB emulation mode.");

	imagingmode=0;
    PsychCopyInIntegerArg(8,FALSE,&imagingmode);
    if(imagingmode < 0) PsychErrorExitMsg(PsychError_user, "Invalid imaging mode provided (See 'help PsychImagingMode' for usage info).");
	if (imagingmode!=0 && EmulateOldPTB) PsychErrorExitMsg(PsychError_user, "Sorry, imaging pipeline functions are not supported in OS-9 PTB emulation mode.");
	
    //set the video mode to change the pixel size.  TO DO: Set the rect and the default color  
    PsychGetScreenSettings(screenNumber, &screenSettings);    
    PsychInitDepthStruct(&(screenSettings.depth));
    PsychCopyDepthStruct(&(screenSettings.depth), &useDepth);

    // Here is where all the work goes on:

    // If the screen is not already captured then to that:
    if(~PsychIsScreenCaptured(screenNumber)) {
        PsychCaptureScreen(screenNumber);

        settingsMade=PsychSetScreenSettings(screenNumber, &screenSettings);
        //Capturing the screen and setting its settings always occur in conjunction
        //There should be a check above to see if the display is captured and openWindow is attempting to chang
        //the bit depth
    }

#if PSYCH_SYSTEM == PSYCH_WINDOWS
    // On M$-Windows we currently only support - and therefore require >= 30 bpp color depth.
    if (PsychGetScreenDepthValue(screenNumber) < 30) {
      // Display running at less than 30 bpp. OpenWindow will fail on M$-Windows anyway, so let's abort
      // now.

      // Release the captured screen:
        PsychReleaseScreen(screenNumber);

	// Output warning text:
        printf("PTB-ERROR: Your display screen %i is not running at the required color depth of at least 30 bit.\n", screenNumber);
        printf("PTB-ERROR: The current setting is %i bit color depth..\n", PsychGetScreenDepthValue(screenNumber));
        printf("PTB-ERROR: This will not work on Microsoft Windows operating systems.\n");
        printf("PTB-ERROR: Please use the 'Display settings' control panel of Windows to change the color depth to\n");
        printf("PTB-ERROR: 32 bits per pixel ('True color' or 'Highest' setting) and then retry. It may be neccessary\n");
        printf("PTB-ERROR: to restart Matlab after applying the change...\n");
        fflush(NULL);

	// Abort with Matlab error:
	PsychErrorExitMsg(PsychError_user, "Insufficient color depth setting for display device (smaller than 30 bpp).");
    }

#endif

    //if (PSYCH_DEBUG == PSYCH_ON) printf("Entering PsychOpenOnscreenWindow\n");
    PsychCopyDepthStruct(&(screenSettings.depth), &useDepth);
    didWindowOpen=PsychOpenOnscreenWindow(&screenSettings, &windowRecord, numWindowBuffers, stereomode, rect, multiSample);

    if (!didWindowOpen) {
        PsychReleaseScreen(screenNumber);

        // We use this dirty hack to exit with an error, but without printing
        // an error message. The specific error message has been printed in
        // PsychOpenOnscreenWindow() already..
        PsychErrMsgTxt("");
    }

    // Sufficient display depth for full alpha-blending and such?
    if (PsychGetScreenDepthValue(screenNumber) < 24) {
        // Nope. Output a little warning.
        printf("PTB-WARNING: Your display screen %i is not running at 24 bit color depth or higher.\n", screenNumber);
        printf("PTB-WARNING: The current setting is %i bit color depth..\n", PsychGetScreenDepthValue(screenNumber));
        printf("PTB-WARNING: This could cause failure to work correctly or visual artifacts in stimuli\n");
        printf("PTB-WARNING: that involve Alpha-Blending. It can also cause drastically reduced color resolution\n");
        printf("PTB-WARNING: for your stimuli! Please try to switch your display to 'True Color' (Windows)\n");
        printf("PTB-WARNING: our 'Millions of Colors' (MacOS-X) to get rid of this warning and the visual artifacts.\n");
        fflush(NULL);
    }
    
	// Define clear color: This depends on the color range of our onscreen window...
    isArgThere=PsychCopyInColorArg(kPsychUseDefaultArgPosition, FALSE, &color); //get from user
    if(!isArgThere) PsychLoadColorStruct(&color, kPsychIndexColor, PsychGetWhiteValueFromWindow(windowRecord)); //or use the default
    PsychCoerceColorMode(&color);

	// Initialize internal image processing pipeline if requested:
	PsychInitializeImagingPipeline(windowRecord, imagingmode);
	
	// On OS-X, if we are int quad-buffered frame sequential stereo mode, we automatically generate
	// blue-line-sync style sync lines for use with stereo shutter glasses. We don't do this
	// by default on Windows or Linux: These systems either don't have stereo capable hardware,
	// or they have some and its drivers already take care of sync signal generation.
	if ((PSYCH_SYSTEM == PSYCH_OSX) && (windowRecord->stereomode==kPsychOpenGLStereo)) {
		if (PsychPrefStateGet_Verbosity()>3) printf("PTB-INFO: Enabling internal blue line sync renderer for quad-buffered stereo...\n");
		PsychPipelineAddBuiltinFunctionToHook(windowRecord, "LeftFinalizerBlitChain", "Builtin:RenderStereoSyncLine", TRUE, "");
		PsychPipelineEnableHook(windowRecord, "LeftFinalizerBlitChain");		
		PsychPipelineAddBuiltinFunctionToHook(windowRecord, "RightFinalizerBlitChain", "Builtin:RenderStereoSyncLine", TRUE, "");
		PsychPipelineEnableHook(windowRecord, "RightFinalizerBlitChain");		
	}

	// Activate new onscreen window for userspace drawing: If imaging pipeline is active, this
	// will bind the correct rendertargets for the first time:
    PsychSetGLContext(windowRecord);
	PsychSetDrawingTarget(windowRecord);

    // Set the clear color and perform a backbuffer-clear:
    PsychConvertColorToDoubleVector(&color, windowRecord, dVals);
    glClearColor(dVals[0], dVals[1], dVals[2], dVals[3]);
    glClear(GL_COLOR_BUFFER_BIT);

    // Mark end of drawing op. This is needed for single buffered drawing:
    PsychFlushGL(windowRecord);

    // Make sure no OpenGL errors happened up to this point:
    PsychTestForGLErrors();

    // If we are in logo-startup mode (former blue-screen mode) and double-buffering
    // is enabled, then do an initial bufferswap & clear, so the display starts in
    // the user selected background color instead of staying at the blue screen or
    // logo display until the Matlab script first calls 'Flip'.
    if ((PsychPrefStateGet_VisualDebugLevel()>=4) && numWindowBuffers>=2) {
      // Do immediate bufferswap by an internal call to Screen('Flip'). This will also
	  // take care of clearing the backbuffer in preparation of first userspace drawing
	  // commands and such...
	  PsychFlipWindowBuffers(windowRecord, 0, 0, 0, 0, &dummy1, &dummy2, &dummy3, &dummy4);
      // Display now shows background color, so user knows that PTB's 'OpenWindow'
      // procedure is successfully finished.
    }

    PsychTestForGLErrors();

    //Return the window index and the rect argument.
    PsychCopyOutDoubleArg(1, FALSE, windowRecord->windowIndex);

	 // rect argument needs special treatment in stereo mode:
	 if (windowRecord->stereomode==kPsychFreeFusionStereo || windowRecord->stereomode==kPsychFreeCrossFusionStereo) {
			// Special case for stereo: Only half the real window width:
			PsychMakeRect(&rect, windowRecord->rect[kPsychLeft],windowRecord->rect[kPsychTop],
							  windowRecord->rect[kPsychLeft] + PsychGetWidthFromRect(windowRecord->rect)/2,windowRecord->rect[kPsychBottom]);
	 }
	 else {
			// Normal case:
			PsychMakeRect(&rect, windowRecord->rect[kPsychLeft],windowRecord->rect[kPsychTop],windowRecord->rect[kPsychRight],windowRecord->rect[kPsychBottom]);
	 }
    PsychCopyOutRectArg(2, FALSE, rect);

    return(PsychError_none);   
}
PsychError SCREENOpenWindow(void) 

{
    int						screenNumber, numWindowBuffers, stereomode, multiSample, imagingmode;
    PsychRectType 			rect, screenrect;
    PsychColorType			color;
    PsychColorModeType  	mode; 
    boolean					isArgThere, settingsMade, didWindowOpen, useAGL;
    PsychScreenSettingsType	screenSettings;
    PsychWindowRecordType	*windowRecord;
    double dVals[4];
    PsychDepthType			specifiedDepth, possibleDepths, currentDepth, useDepth;
	int dummy1;
	double dummy2, dummy3, dummy4;
	Boolean EmulateOldPTB = PsychPrefStateGet_EmulateOldPTB();
    
	//just for debugging
    //if (PSYCH_DEBUG == PSYCH_ON) printf("Entering SCREENOpen\n");

    //all sub functions should have these two lines
    PsychPushHelp(useString, synopsisString, seeAlsoString);
    if(PsychIsGiveHelp()){PsychGiveHelp();return(PsychError_none);};

    //cap the number of inputs
    PsychErrorExit(PsychCapNumInputArgs(8));   //The maximum number of inputs
    PsychErrorExit(PsychCapNumOutputArgs(2));  //The maximum number of outputs

    //get the screen number from the windowPtrOrScreenNumber.  This also checks to make sure that the specified screen exists.  
    PsychCopyInScreenNumberArg(kPsychUseDefaultArgPosition, TRUE, &screenNumber);
    if(screenNumber==-1)
        PsychErrorExitMsg(PsychError_user, "The specified onscreen window has no ancestral screen."); 

    /*
      The depth checking is ugly because of this stupid depth structure stuff.  
      Instead get a descriptor of the current video settings, change the depth field,
      and pass it to a validate function wich searches a list of valid video modes for the display.
      There seems to be no point in checking the depths alone because the legality of a particular
      depth depends on the other settings specified below.  Its probably best to wait until we have
      digested all settings and then test the full mode, declarin an invalid
      mode and not an invalid pixel size.  We could notice when the depth alone is specified 
      and in that case issue an invalid depth value.
     */  

    //find the PixelSize first because the color specifier depends on the screen depth.  
    PsychInitDepthStruct(&currentDepth);  //get the current depth
    PsychGetScreenDepth(screenNumber, &currentDepth);
    PsychInitDepthStruct(&possibleDepths); //get the possible depths
    PsychGetScreenDepths(screenNumber, &possibleDepths);

    #if PSYCH_SYSTEM == PSYCH_OSX || PSYCH_SYSTEM == PSYCH_WINDOWS
       // MK Experimental Hack: Add the special depth values 64 and 128 to the depth struct. This should 
       // allows for 16 bpc, 32 bpc floating point color buffers on the latest ATI and NVidia hardware.
	   // "Should" means: It doesn't really work with any current driver, but we leave the testcode in
	   // in the hope for future OS and driver releases ;-)
       // Unfortunately at this point of the init sequence, we are not able
       // to check if these formats are supported by the hardware. Ugly ugly ugly...
       PsychAddValueToDepthStruct(64, &possibleDepths);
       PsychAddValueToDepthStruct(128, &possibleDepths);
    #endif

//    #if PSYCH_SYSTEM == PSYCH_OSX || PSYCH_SYSTEM == PSYCH_LINUX
		// On MacOS/X and Linux with ATI Radeon X1000/HD2000/HD3000 hardware and the special
		// kernel support driver installed, we should be able to configure the hardwares
		// framebuffers into ABGR2101010 mode, ie. 2 bits alpha, 10 bpc for red, green, blue.
		// This needs support from the imaging pipeline, or manually converted stimuli, as
		// the GPU doesn't format pixel data properly, only the CRTC scans out in that format.
		// Anyway, allow this setting on OS/X and Linux:
		
		// Update: Some FireGL cards (2008 and later) claim to support this on MS-Windows. Enable
		// this option on Windows as well, so it is at least testable:
		PsychAddValueToDepthStruct(30, &possibleDepths);
//    #endif


    PsychInitDepthStruct(&specifiedDepth); //get the requested depth and validate it.  
    isArgThere = PsychCopyInSingleDepthArg(4, FALSE, &specifiedDepth);

    PsychInitDepthStruct(&useDepth);
    if(isArgThere){ //if the argument is there check that the screen supports it...
        if(!PsychIsMemberDepthStruct(&specifiedDepth, &possibleDepths))
            PsychErrorExit(PsychError_invalidDepthArg);
        else
            PsychCopyDepthStruct(&useDepth, &specifiedDepth);
    }else //otherwise use the default
        PsychCopyDepthStruct(&useDepth, &currentDepth);

    // Initialize the rect argument to the screen rectangle:
    PsychGetScreenRect(screenNumber, rect); 	//get the rect describing the screen bounds.  This is the default Rect.  

    // Override it with a user supplied rect, if one was supplied:
    isArgThere=PsychCopyInRectArg(kPsychUseDefaultArgPosition, FALSE, rect );
    if (IsPsychRectEmpty(rect)) PsychErrorExitMsg(PsychError_user, "OpenWindow called with invalid (empty) rect argument.");

	if (PSYCH_SYSTEM == PSYCH_OSX) {
		// OS/X system: Need to decide if we use a Carbon window + AGL
		// or a fullscreen context with CGL:
		
		// Default to AGL, switch to CGL if below constraints are met:
		useAGL = TRUE;
	
		// Window rect provided which has a different size than screen?

		// We do not use windowed mode if the provided window rectangle either
		// matches the target screens rectangle (and therefore its exact size)
		// or its screens global rectangle.
		PsychGetScreenRect(screenNumber, screenrect);
		if (PsychMatchRect(screenrect, rect)) useAGL=FALSE;
		PsychGetGlobalScreenRect(screenNumber, screenrect);
		if (PsychMatchRect(screenrect, rect)) useAGL=FALSE;

		// Override for use on f$%#$Fd OS/X 10.5.3 - 10.5.6 with NVidia GF 8800 GPU's:
		if (PsychPrefStateGet_ConserveVRAM() & kPsychUseAGLCompositorForFullscreenWindows) useAGL = TRUE;
	}
	else {
		// Non OS/X system: Do not use AGL ;-)
		useAGL = FALSE;
	}
	
    //find the number of specified buffers. 

    //OS X:	The number of backbuffers is not a property of the display mode but an attribute of the pixel format.
    //		Therefore the value is held by a window record and not a screen record.    

    numWindowBuffers=2;	
    PsychCopyInIntegerArg(5,FALSE,&numWindowBuffers);
    if(numWindowBuffers < 1 || numWindowBuffers > kPsychMaxNumberWindowBuffers) PsychErrorExit(PsychError_invalidNumberBuffersArg);

    // MK: Check for optional spec of stereoscopic display: 0 (the default) = monoscopic viewing.
    // 1 == Stereo output via OpenGL built-in stereo facilities: This will drive any kind of
    // stereo display hardware that is directly supported by MacOS-X.
    // 2/3 == Stereo output via compressed frame output: Only one backbuffer is used for both
    // views: The left view image is put into the top-half of the screen, the right view image
    // is put into the bottom half of the screen. External hardware demangles this combi-image
    // again into two separate images. CrystalEyes seems to be able to do this. One looses half
    // of the vertical resolution, but potentially gains refresh rate...
    // Future PTB version may include different stereo algorithms with an id > 1, e.g., 

    // anaglyph stereo, interlaced stereo, ...

    stereomode=0;
    PsychCopyInIntegerArg(6,FALSE,&stereomode);
    if(stereomode < 0 || stereomode > 10) PsychErrorExitMsg(PsychError_user, "Invalid stereomode provided (Valid between 0 and 10).");
	if (stereomode!=0 && EmulateOldPTB) PsychErrorExitMsg(PsychError_user, "Sorry, stereo display functions are not supported in OS-9 PTB emulation mode.");

    multiSample=0;
    PsychCopyInIntegerArg(7,FALSE,&multiSample);
    if(multiSample < 0) PsychErrorExitMsg(PsychError_user, "Invalid multisample value provided (Valid are positive numbers >= 0).");
	if (multiSample!=0 && EmulateOldPTB) PsychErrorExitMsg(PsychError_user, "Sorry, anti-aliasing functions are not supported in OS-9 PTB emulation mode.");

	imagingmode=0;
    PsychCopyInIntegerArg(8,FALSE,&imagingmode);
    if(imagingmode < 0) PsychErrorExitMsg(PsychError_user, "Invalid imaging mode provided (See 'help PsychImagingMode' for usage info).");
	if (imagingmode!=0 && EmulateOldPTB) PsychErrorExitMsg(PsychError_user, "Sorry, imaging pipeline functions are not supported in OS-9 PTB emulation mode.");
	
	// We require use of the imaging pipeline if stereomode for dualwindow display is requested.
	// This makes heavy use of FBO's and blit operations, so imaging pipeline is needed.
	if (stereomode==kPsychDualWindowStereo) {
		// Dual window stereo requested, but imaging pipeline not enabled. Enable it:
		imagingmode|= kPsychNeedFastBackingStore;
		if (PsychPrefStateGet_Verbosity()>3) printf("PTB-INFO: Trying to enable imaging pipeline for dual-window stereo display mode...\n");
	}
	
    //set the video mode to change the pixel size.  TO DO: Set the rect and the default color  
    PsychGetScreenSettings(screenNumber, &screenSettings);    
    PsychInitDepthStruct(&(screenSettings.depth));
    PsychCopyDepthStruct(&(screenSettings.depth), &useDepth);

    // Here is where all the work goes on:

    // If the screen is not already captured then to that:
    if(!PsychIsScreenCaptured(screenNumber) && !useAGL) {
        PsychCaptureScreen(screenNumber);

		// We disable the call to PsychSetScreenSettings here: Its not useful, as it
		// could only change color depth - which is something we don't want to do anyway here.
		// If people want to change displays settings, they should use Screen('Resolution') instead,
		// which is a more clever interface to PsychSetScreenSettings().
		
        // settingsMade=PsychSetScreenSettings(screenNumber, &screenSettings);
        //Capturing the screen and setting its settings always occur in conjunction
        //There should be a check above to see if the display is captured and openWindow is attempting to chang
        //the bit depth
    }

#if PSYCH_SYSTEM == PSYCH_WINDOWS
    // On M$-Windows we currently only support - and therefore require >= 30 bpp color depth.
    if (PsychGetScreenDepthValue(screenNumber) < 30) {
		// Display running at less than 30 bpp. OpenWindow will fail on M$-Windows anyway, so let's abort
		// now.

		// Output warning text:
        printf("PTB-ERROR: Your display screen %i is not running at the required color depth of at least 30 bit.\n", screenNumber);
        printf("PTB-ERROR: The current setting is %i bit color depth..\n", PsychGetScreenDepthValue(screenNumber));
        printf("PTB-ERROR: This will not work on Microsoft Windows operating systems.\n");
        printf("PTB-ERROR: Please use the 'Display settings' control panel of Windows to change the color depth to\n");
        printf("PTB-ERROR: 32 bits per pixel ('True color' or 'Highest' setting) and then retry. It may be neccessary\n");
        printf("PTB-ERROR: to restart Matlab after applying the change...\n");
        fflush(NULL);

		// Release the captured screen:
		PsychRestoreScreenSettings(screenNumber);
		PsychReleaseScreen(screenNumber);

        // Reset master assignment to prepare possible further dual-window config operations:
		sharedContextWindow = NULL;

		// Abort with Matlab error:
		PsychErrorExitMsg(PsychError_user, "Insufficient color depth setting for display device (smaller than 30 bpp).");
    }

#endif

    //if (PSYCH_DEBUG == PSYCH_ON) printf("Entering PsychOpenOnscreenWindow\n");
    PsychCopyDepthStruct(&(screenSettings.depth), &useDepth);
	
	// Create the onscreen window and perform initialization of everything except
	// imaging pipeline and a few other special quirks. If sharedContextWindow is non-NULL,
	// the new window will share its OpenGL context ressources with sharedContextWindow.
	// This is typically used for dual-window stereo mode. Btw. If imaging pipeline is really
	// active, we force multiSample to zero: This way the system backbuffer / pixelformat
	// is enabled without multisampling support, as we do all the multisampling stuff ourselves
	// within the imaging pipeline with multisampled drawbuffer FBO's...
    didWindowOpen=PsychOpenOnscreenWindow(&screenSettings, &windowRecord, numWindowBuffers, stereomode, rect, ((imagingmode==0 || imagingmode==kPsychNeedFastOffscreenWindows) ? multiSample : 0), sharedContextWindow);
    if (!didWindowOpen) {
        if (!useAGL) {
			PsychRestoreScreenSettings(screenNumber);
			PsychReleaseScreen(screenNumber);
		}

		// Reset master assignment to prepare possible further dual-window config operations:
		sharedContextWindow = NULL;

        // We use this dirty hack to exit with an error, but without printing
        // an error message. The specific error message has been printed in
        // PsychOpenOnscreenWindow() already..
        PsychErrMsgTxt("");
    }

    // Sufficient display depth for full alpha-blending and such?
    if (PsychGetScreenDepthValue(screenNumber) < 24) {
        // Nope. Output a little warning.
        printf("PTB-WARNING: Your display screen %i is not running at 24 bit color depth or higher.\n", screenNumber);
        printf("PTB-WARNING: The current setting is %i bit color depth..\n", PsychGetScreenDepthValue(screenNumber));
        printf("PTB-WARNING: This could cause failure to work correctly or visual artifacts in stimuli\n");
        printf("PTB-WARNING: that involve Alpha-Blending. It can also cause drastically reduced color resolution\n");
        printf("PTB-WARNING: for your stimuli! Please try to switch your display to 'True Color' (Windows)\n");
        printf("PTB-WARNING: our 'Millions of Colors' (MacOS-X) to get rid of this warning and the visual artifacts.\n");
        fflush(NULL);
    }
    
	// Define clear color: This depends on the color range of our onscreen window...
    isArgThere=PsychCopyInColorArg(kPsychUseDefaultArgPosition, FALSE, &color); //get from user
    if(!isArgThere) PsychLoadColorStruct(&color, kPsychIndexColor, PsychGetWhiteValueFromWindow(windowRecord)); //or use the default
    PsychCoerceColorMode(&color);

	// Special setup code for dual window stereomode:
	if (stereomode == kPsychDualWindowStereo) {
		if (sharedContextWindow) {
			// This is creation & setup of the slave onscreen window, ie. the one
			// representing the right-eye view. This window doesn't do much. It
			// is not used or referenced in the users experiment script. It receives
			// its final image content during Screen('Flip') operation of the master
			// onscreen window, then gets flipped in sync with the master window.
			
			// Ok, we already have the slave window open and it shares its OpenGL context
			// with the master window. Reset its internal reference to the master:
			windowRecord->slaveWindow = NULL;
			
			// Reset imagingmode for this window prior to imaging pipeline setup. This
			// window is totally passive so it doesn't need the imaging pipeline.
			imagingmode = 0;
						
			// Assign this window to the master window as a slave:
			sharedContextWindow->slaveWindow = windowRecord;
			
			// Reset master assignment to prepare possible further dual-window config operations:
			sharedContextWindow = NULL;

			// Activate the IdentitiyBlitChain for the slave window and add a single identity blit
			// operation to it: This is needed in PsychPreFlipOperations() for final copy of stimulus
			// image into this slave window:
			PsychPipelineAddBuiltinFunctionToHook(windowRecord, "IdentityBlitChain", "Builtin:IdentityBlit", INT_MAX, "");
			PsychPipelineEnableHook(windowRecord, "IdentityBlitChain");

			if (PsychPrefStateGet_Verbosity()>3) printf("PTB-INFO: Created master-slave window relationship for dual-window stereo display mode...\n");

			// Special config finished. The master-slave combo should work from now on...
		}
		else {
			// This is initial setup & creation of the master onscreen window, ie. the one
			// representing the left-eye view and doing all the heavy work, acting as a
			// proxy for both windows.
			
			// Not much to do here. Just store its windowRecord as a reference for creation
			// of the slave window. We'll need it for that purpose...
			sharedContextWindow = windowRecord;
		}
	}

	// Set special half-width flag for window if we are either in a dual-display/dual-view stereo mode or if
	// if is requested as part of the imagingMode flag. This will cause PTB 2D drawing routines and window size
	// query routines etc. to return an effective window width or window rect only half the real width.
	if (windowRecord->stereomode==kPsychFreeFusionStereo || windowRecord->stereomode==kPsychFreeCrossFusionStereo || (imagingmode & kPsychHalfWidthWindow)) {
		windowRecord->specialflags = windowRecord->specialflags | kPsychHalfWidthWindow;
		imagingmode = imagingmode & (~kPsychHalfWidthWindow);
	}

	// Similar handling for windows of half the real height, except that none of our built-in stereo modes requires these,
	// so this is only done on request from external code via the imagingmode flag kPsychHalfHeightWindow.
	// One use of this is when using interleaved line stereo mode (PsychImaging(...'InterleavedLineStereo')) where windows
	// only have a useable net height of half their physical height:
	if (imagingmode & kPsychHalfHeightWindow) {
		windowRecord->specialflags = windowRecord->specialflags | kPsychHalfHeightWindow;
		imagingmode = imagingmode & (~kPsychHalfHeightWindow);
	}

	// Initialize internal image processing pipeline if requested:
	PsychInitializeImagingPipeline(windowRecord, imagingmode, multiSample);
	
	// On OS-X, if we are in quad-buffered frame sequential stereo mode, we automatically generate
	// blue-line-sync style sync lines for use with stereo shutter glasses. We don't do this
	// by default on Windows or Linux: These systems either don't have stereo capable hardware,
	// or they have some and its drivers already take care of sync signal generation.
	if ((PSYCH_SYSTEM == PSYCH_OSX) && (windowRecord->stereomode==kPsychOpenGLStereo)) {
		if (PsychPrefStateGet_Verbosity()>3) printf("PTB-INFO: Enabling internal blue line sync renderer for quad-buffered stereo...\n");
		PsychPipelineAddBuiltinFunctionToHook(windowRecord, "LeftFinalizerBlitChain", "Builtin:RenderStereoSyncLine", INT_MAX, "");
		PsychPipelineEnableHook(windowRecord, "LeftFinalizerBlitChain");		
		PsychPipelineAddBuiltinFunctionToHook(windowRecord, "RightFinalizerBlitChain", "Builtin:RenderStereoSyncLine", INT_MAX, "");
		PsychPipelineEnableHook(windowRecord, "RightFinalizerBlitChain");		
	}

	// Activate new onscreen window for userspace drawing: If imaging pipeline is active, this
	// will bind the correct rendertargets for the first time:
	PsychSetDrawingTarget(windowRecord);

    // Set the clear color and perform a backbuffer-clear:
    PsychConvertColorToDoubleVector(&color, windowRecord, windowRecord->clearColor);
	PsychGLClear(windowRecord);

    // Mark end of drawing op. This is needed for single buffered drawing:
    PsychFlushGL(windowRecord);

    // Make sure no OpenGL errors happened up to this point:
    PsychTestForGLErrors();

    // If we are in logo-startup mode (former blue-screen mode) and double-buffering
    // is enabled, then do an initial bufferswap & clear, so the display starts in
    // the user selected background color instead of staying at the blue screen or
    // logo display until the Matlab script first calls 'Flip'.
    if ((PsychPrefStateGet_VisualDebugLevel()>=4) && numWindowBuffers>=2) {
      // Do immediate bufferswap by an internal call to Screen('Flip'). This will also
	  // take care of clearing the backbuffer in preparation of first userspace drawing
	  // commands and such...
	  PsychFlipWindowBuffers(windowRecord, 0, 0, 0, 0, &dummy1, &dummy2, &dummy3, &dummy4);
      // Display now shows background color, so user knows that PTB's 'OpenWindow'
      // procedure is successfully finished.
    }

    PsychTestForGLErrors();

    //Return the window index and the rect argument.
    PsychCopyOutDoubleArg(1, FALSE, windowRecord->windowIndex);

	// rect argument needs special treatment in stereo mode:
	PsychMakeRect(&rect, windowRecord->rect[kPsychLeft], windowRecord->rect[kPsychTop],
					windowRecord->rect[kPsychLeft] + PsychGetWidthFromRect(windowRecord->rect)/((windowRecord->specialflags & kPsychHalfWidthWindow) ? 2 : 1),
					windowRecord->rect[kPsychTop] + PsychGetHeightFromRect(windowRecord->rect)/((windowRecord->specialflags & kPsychHalfHeightWindow) ? 2 : 1));

    PsychCopyOutRectArg(2, FALSE, rect);

    return(PsychError_none);   
}
PsychError SCREENOpenWindow(void) 

{
    int						screenNumber, numWindowBuffers, stereomode, multiSample, imagingmode, specialflags;
    PsychRectType 			rect, screenrect;
    PsychColorType			color;
    psych_bool				isArgThere, didWindowOpen, useAGL;
    PsychScreenSettingsType	screenSettings;
    PsychWindowRecordType	*windowRecord;
    PsychDepthType			specifiedDepth, possibleDepths, currentDepth, useDepth;
	int                     dummy1;
	double                  dummy2, dummy3, dummy4;

	psych_bool EmulateOldPTB = PsychPrefStateGet_EmulateOldPTB();

    //all sub functions should have these two lines
    PsychPushHelp(useString, synopsisString, seeAlsoString);
    if(PsychIsGiveHelp()){PsychGiveHelp();return(PsychError_none);};

    //cap the number of inputs
    PsychErrorExit(PsychCapNumInputArgs(9));   //The maximum number of inputs
    PsychErrorExit(PsychCapNumOutputArgs(2));  //The maximum number of outputs

    //get the screen number from the windowPtrOrScreenNumber.  This also checks to make sure that the specified screen exists.  
    PsychCopyInScreenNumberArg(kPsychUseDefaultArgPosition, TRUE, &screenNumber);
    if(screenNumber==-1)
        PsychErrorExitMsg(PsychError_user, "The specified onscreen window has no ancestral screen."); 

    /*
      The depth checking is ugly because of this stupid depth structure stuff.  
      Instead get a descriptor of the current video settings, change the depth field,
      and pass it to a validate function wich searches a list of valid video modes for the display.
      There seems to be no point in checking the depths alone because the legality of a particular
      depth depends on the other settings specified below.  Its probably best to wait until we have
      digested all settings and then test the full mode, declarin an invalid
      mode and not an invalid pixel size.  We could notice when the depth alone is specified 
      and in that case issue an invalid depth value.
     */  

    //find the PixelSize first because the color specifier depends on the screen depth.  
    PsychInitDepthStruct(&currentDepth);  //get the current depth
    PsychGetScreenDepth(screenNumber, &currentDepth);
    PsychInitDepthStruct(&possibleDepths); //get the possible depths
    PsychGetScreenDepths(screenNumber, &possibleDepths);

    #if PSYCH_SYSTEM == PSYCH_OSX || PSYCH_SYSTEM == PSYCH_WINDOWS
       // MK Experimental Hack: Add the special depth values 64 and 128 to the depth struct. This should 
       // allows for 16 bpc, 32 bpc floating point color buffers on the latest ATI and NVidia hardware.
	   // "Should" means: It doesn't really work with any current driver, but we leave the testcode in
	   // in the hope for future OS and driver releases ;-)
       // Unfortunately at this point of the init sequence, we are not able
       // to check if these formats are supported by the hardware. Ugly ugly ugly...
       PsychAddValueToDepthStruct(64, &possibleDepths);
       PsychAddValueToDepthStruct(128, &possibleDepths);
    #endif

//    #if PSYCH_SYSTEM == PSYCH_OSX || PSYCH_SYSTEM == PSYCH_LINUX
		// On MacOS/X and Linux with ATI Radeon X1000/HD2000/HD3000 hardware and the special
		// kernel support driver installed, we should be able to configure the hardwares
		// framebuffers into ABGR2101010 mode, ie. 2 bits alpha, 10 bpc for red, green, blue.
		// This needs support from the imaging pipeline, or manually converted stimuli, as
		// the GPU doesn't format pixel data properly, only the CRTC scans out in that format.
		// Anyway, allow this setting on OS/X and Linux:
		
		// Update: Some FireGL cards (2008 and later) claim to support this on MS-Windows. Enable
		// this option on Windows as well, so it is at least testable:
		PsychAddValueToDepthStruct(30, &possibleDepths);
//    #endif


    PsychInitDepthStruct(&specifiedDepth); //get the requested depth and validate it.  
    isArgThere = PsychCopyInSingleDepthArg(4, FALSE, &specifiedDepth);

    PsychInitDepthStruct(&useDepth);
    if(isArgThere){ //if the argument is there check that the screen supports it...
        if(!PsychIsMemberDepthStruct(&specifiedDepth, &possibleDepths))
            PsychErrorExit(PsychError_invalidDepthArg);
        else
            PsychCopyDepthStruct(&useDepth, &specifiedDepth);
    }else //otherwise use the default
        PsychCopyDepthStruct(&useDepth, &currentDepth);

    // Initialize the rect argument to the screen rectangle:
    PsychGetGlobalScreenRect(screenNumber, rect); 	//get the rect describing the screen bounds.  This is the default Rect.  

    // Override it with a user supplied rect, if one was supplied:
    isArgThere=PsychCopyInRectArg(kPsychUseDefaultArgPosition, FALSE, rect );
    if (IsPsychRectEmpty(rect)) PsychErrorExitMsg(PsychError_user, "OpenWindow called with invalid (empty) rect argument.");

	if (PSYCH_SYSTEM == PSYCH_OSX) {
		// OS/X system: Need to decide if we use a Carbon window + AGL
		// or a fullscreen context with CGL:
		
		// Default to AGL, switch to CGL if below constraints are met:
		useAGL = TRUE;
	
		// Window rect provided which has a different size than screen?

		// We do not use windowed mode if the provided window rectangle either
		// matches the target screens rectangle (and therefore its exact size)
		// or its screens global rectangle.
		PsychGetScreenRect(screenNumber, screenrect);
		if (PsychMatchRect(screenrect, rect)) useAGL=FALSE;
		PsychGetGlobalScreenRect(screenNumber, screenrect);
		if (PsychMatchRect(screenrect, rect)) useAGL=FALSE;

		// Override for use on f$%#$Fd OS/X 10.5.3 - 10.5.6 with NVidia GF 8800 GPU's:
		if (PsychPrefStateGet_ConserveVRAM() & kPsychUseAGLCompositorForFullscreenWindows) useAGL = TRUE;
	}
	else {
		// Non OS/X system: Do not use AGL ;-)
		useAGL = FALSE;
	}
	
    //find the number of specified buffers. 

    //OS X:	The number of backbuffers is not a property of the display mode but an attribute of the pixel format.
    //		Therefore the value is held by a window record and not a screen record.    

    numWindowBuffers=2;	
    PsychCopyInIntegerArg(5,FALSE,&numWindowBuffers);
    if(numWindowBuffers < 1 || numWindowBuffers > kPsychMaxNumberWindowBuffers) PsychErrorExit(PsychError_invalidNumberBuffersArg);

    stereomode=0;
    PsychCopyInIntegerArg(6,FALSE,&stereomode);
    if(stereomode < 0 || stereomode > 11) PsychErrorExitMsg(PsychError_user, "Invalid stereomode provided (Valid between 0 and 11).");
	if (stereomode!=0 && EmulateOldPTB) PsychErrorExitMsg(PsychError_user, "Sorry, stereo display functions are not supported in OS-9 PTB emulation mode.");

    multiSample=0;
    PsychCopyInIntegerArg(7,FALSE,&multiSample);
    if(multiSample < 0) PsychErrorExitMsg(PsychError_user, "Invalid multisample value provided (Valid are positive numbers >= 0).");
	if (multiSample!=0 && EmulateOldPTB) PsychErrorExitMsg(PsychError_user, "Sorry, anti-aliasing functions are not supported in OS-9 PTB emulation mode.");

	imagingmode=0;
    PsychCopyInIntegerArg(8,FALSE,&imagingmode);
    if(imagingmode < 0) PsychErrorExitMsg(PsychError_user, "Invalid imaging mode provided (See 'help PsychImagingMode' for usage info).");
	if (imagingmode!=0 && EmulateOldPTB) PsychErrorExitMsg(PsychError_user, "Sorry, imaging pipeline functions are not supported in OS-9 PTB emulation mode.");
	
	specialflags=0;
    PsychCopyInIntegerArg(9,FALSE,&specialflags);
    if (specialflags < 0 || (specialflags > 0 && specialflags!=kPsychGUIWindow)) PsychErrorExitMsg(PsychError_user, "Invalid 'specialflags' provided.");

	// We require use of the imaging pipeline if stereomode for dualwindow display is requested.
	// This makes heavy use of FBO's and blit operations, so imaging pipeline is needed.
	if ((stereomode==kPsychDualWindowStereo) || (imagingmode & kPsychNeedDualWindowOutput)) {
		// Dual window stereo requested, but imaging pipeline not enabled. Enable it:
		imagingmode|= kPsychNeedFastBackingStore;
		if (PsychPrefStateGet_Verbosity()>3) printf("PTB-INFO: Trying to enable imaging pipeline for dual-window stereo display mode or dual-window output mode...\n");
	}
	
    //set the video mode to change the pixel size.  TO DO: Set the rect and the default color  
    PsychGetScreenSettings(screenNumber, &screenSettings);    
    PsychInitDepthStruct(&(screenSettings.depth));
    PsychCopyDepthStruct(&(screenSettings.depth), &useDepth);

    // Here is where all the work goes on:

    // If the screen is not already captured then to that:
    if(!PsychIsScreenCaptured(screenNumber) && !useAGL) {
        PsychCaptureScreen(screenNumber);
    }

#if PSYCH_SYSTEM == PSYCH_WINDOWS
    // On M$-Windows we currently only support - and therefore require >= 30 bpp color depth.
    if (PsychGetScreenDepthValue(screenNumber) < 30) {
		// Display running at less than 30 bpp. OpenWindow will fail on M$-Windows anyway, so let's abort
		// now.

		// Output warning text:
        printf("PTB-ERROR: Your display screen %i is not running at the required color depth of at least 30 bit.\n", screenNumber);
        printf("PTB-ERROR: The current setting is %i bit color depth..\n", PsychGetScreenDepthValue(screenNumber));
        printf("PTB-ERROR: This will not work on Microsoft Windows operating systems.\n");
        printf("PTB-ERROR: Please use the 'Display settings' control panel of Windows to change the color depth to\n");
        printf("PTB-ERROR: 32 bits per pixel ('True color' or 'Highest' setting) and then retry. It may be neccessary\n");
        printf("PTB-ERROR: to restart Matlab after applying the change...\n");
        fflush(NULL);

		// Release the captured screen:
		PsychRestoreScreenSettings(screenNumber);
		PsychReleaseScreen(screenNumber);

        // Reset master assignment to prepare possible further dual-window config operations:
		sharedContextWindow = NULL;

		// Abort with Matlab error:
		PsychErrorExitMsg(PsychError_user, "Insufficient color depth setting for display device (smaller than 30 bpp).");
    }

#endif

    //if (PSYCH_DEBUG == PSYCH_ON) printf("Entering PsychOpenOnscreenWindow\n");
    PsychCopyDepthStruct(&(screenSettings.depth), &useDepth);
	
	// Create the onscreen window and perform initialization of everything except
	// imaging pipeline and a few other special quirks. If sharedContextWindow is non-NULL,
	// the new window will share its OpenGL context ressources with sharedContextWindow.
	// This is typically used for dual-window stereo mode. Btw. If imaging pipeline is really
	// active, we force multiSample to zero: This way the system backbuffer / pixelformat
	// is enabled without multisampling support, as we do all the multisampling stuff ourselves
	// within the imaging pipeline with multisampled drawbuffer FBO's...
    didWindowOpen=PsychOpenOnscreenWindow(&screenSettings, &windowRecord, numWindowBuffers, stereomode, rect, ((imagingmode==0 || imagingmode==kPsychNeedFastOffscreenWindows) ? multiSample : 0), sharedContextWindow, specialflags);
    if (!didWindowOpen) {
        if (!useAGL) {
			PsychRestoreScreenSettings(screenNumber);
			PsychReleaseScreen(screenNumber);
		}

		// Reset master assignment to prepare possible further dual-window config operations:
		sharedContextWindow = NULL;

        // We use this dirty hack to exit with an error, but without printing
        // an error message. The specific error message has been printed in
        // PsychOpenOnscreenWindow() already..
        PsychErrMsgTxt("");
    }

    // Sufficient display depth for full alpha-blending and such?
    if (PsychGetScreenDepthValue(screenNumber) < 24) {
        // Nope. Output a little warning.
        printf("PTB-WARNING: Your display screen %i is not running at 24 bit color depth or higher.\n", screenNumber);
        printf("PTB-WARNING: The current setting is %i bit color depth..\n", PsychGetScreenDepthValue(screenNumber));
        printf("PTB-WARNING: This could cause failure to work correctly or visual artifacts in stimuli\n");
        printf("PTB-WARNING: that involve Alpha-Blending. It can also cause drastically reduced color resolution\n");
        printf("PTB-WARNING: for your stimuli! Please try to switch your display to 'True Color' (Windows)\n");
        printf("PTB-WARNING: our 'Millions of Colors' (MacOS-X) to get rid of this warning and the visual artifacts.\n");
        fflush(NULL);
    }
    
	// Define clear color: This depends on the color range of our onscreen window...
    isArgThere=PsychCopyInColorArg(kPsychUseDefaultArgPosition, FALSE, &color); //get from user
    if(!isArgThere) PsychLoadColorStruct(&color, kPsychIndexColor, PsychGetWhiteValueFromWindow(windowRecord)); //or use the default
    PsychCoerceColorMode(&color);

    // The imaging pipeline and graphics drivers had over 5 years of time to mature. As of 2012, imaging pipeline based
    // support for fast offscreen windows and for stereoscopic display modes is far superior in performance,
    // robustness, flexibility and convenience to the legacy method which was used in ptb by default so far.
    // Now it is 2012+ and we switch the defaults: If the GPU+driver combo supports it, and usercode doesn't
    // actively opt-out of it, we auto-enable use of FBO backed fast offscreen windows. We don't auto-enable
    // the full pipeline for stereoscopic display modes, but we print some recommendations to the user to
    // consider enabling the full pipeline for stereo display:
    if ((windowRecord->gfxcaps & kPsychGfxCapFBO) && !(PsychPrefStateGet_ConserveVRAM() & kPsychDontAutoEnableImagingPipeline)) {
        // Support for basic use of the PTB imaging pipeline and/or for fast offscreen windows
        // is available - a GPU + driver combo with support for OpenGL framebuffer objects with
        // at least RGBA8 format and rectangle rendertargets.
        // Usercode doesn't disallow automatic use of imaging pipeline or fast offscreen windows,
        // ie. it didn't set the kPsychDontAutoEnableImagingPipeline conserveVRAM flag.
        // Good!
        
        // We will therefore auto-enable use of fast offscreen windows:
        imagingmode |= kPsychNeedFastOffscreenWindows;
        
        // Is a stereomode requested which would benefit from enabling the full imaging pipeline?
        if (stereomode > 0) {
	    if (((stereomode == kPsychOpenGLStereo) && !(windowRecord->gfxcaps & kPsychGfxCapNativeStereo)) || (stereomode == kPsychFrameSequentialStereo)) {
		// Native OpenGL quad-buffered frame-sequential stereo requested, but unsupported by gpu & driver.
		// Or use of our own method requested. We have FBO and framebuffer blit support, so we can roll our
		// own framesequential stereo by use of the imaging pipeline. Enable basic imaging pipeline:
		imagingmode |= kPsychNeedFastBackingStore;

		// Override stereomode to our own homegrown implementation:
		stereomode = kPsychFrameSequentialStereo;
		windowRecord->stereomode = stereomode;

		if (PsychPrefStateGet_Verbosity() > 2) {
		    printf("\n");
		    printf("PTB-INFO: Your script requests use of frame-sequential stereo, but your graphics card\n");
		    printf("PTB-INFO: and driver doesn't support this. I will now fully enable the imaging pipeline\n");
		    printf("PTB-INFO: and use my own home-grown frame-sequential stereo implementation. Note that this\n");
		    printf("PTB-INFO: may not be as robust and high-performance as using a graphics card with native\n");
		    printf("PTB-INFO: frame-sequential stereo support. But let's see what i can do for you...\n\n");
		}
	    }
	    else {
		// Yes: Provide the user with recommendations to enable the pipeline.
		if (!(imagingmode & kPsychNeedFastBackingStore) && (PsychPrefStateGet_Verbosity() > 2)) {
		    printf("\n");
		    printf("PTB-INFO: Your script requests use of a stereoscopic display mode (stereomode = %i).\n", stereomode);
		    printf("PTB-INFO: Stereoscopic stimulus display is usually more flexible, convenient and robust if\n");
		    printf("PTB-INFO: the Psychtoolbox imaging pipeline is enabled. Your graphics card is capable\n");
		    printf("PTB-INFO: of using the pipeline but your script doesn't enable use of the pipeline.\n");
		    printf("PTB-INFO: I recommend you enable use of the pipeline for enhanced stereo stimulus display.\n");
		    printf("PTB-INFO: Have a look at the demoscript ImagingStereoDemo.m on how to do this.\n\n");
		}
	    }
        }
    }

	// Query if OpenGL stereo is natively supported or if our own emulation mode will work:
	if ((((stereomode == kPsychOpenGLStereo) && !(windowRecord->gfxcaps & kPsychGfxCapNativeStereo)) || (stereomode == kPsychFrameSequentialStereo)) &&
	    (!(imagingmode & kPsychNeedFastBackingStore) || (windowRecord->stereomode != kPsychFrameSequentialStereo) || !(windowRecord->gfxcaps & kPsychGfxCapFBO))) {
		// OpenGL native stereo was requested, but is obviously not supported and we can't roll our own implementation either :-(
		printf("\nPTB-ERROR: Asked for OpenGL native stereo (frame-sequential mode) but this doesn't seem to be supported by your graphics hardware or driver.\n");
		printf("PTB-ERROR: Unfortunately using my own implementation via imaging pipeline did not work either, due to lack of hardware support, or because\n");
		printf("PTB-ERROR: did not allow me to auto-enable the pipeline and use this method. This means game over!\n");
		if (PSYCH_SYSTEM == PSYCH_OSX) {
			printf("PTB-ERROR: Frame-sequential stereo should be supported on all recent ATI/AMD and NVidia cards on OS/X, except for the Intel onboard chips,\n");
			printf("PTB-ERROR: at least in fullscreen mode with OS/X 10.5, and also mostly on OS/X 10.4. If it doesn't work, check for OS updates etc.\n\n");
		}
		else {
			printf("PTB-ERROR: Frame-sequential native stereo on Windows or Linux is usually only supported with the professional line of graphics cards\n");
			printf("PTB-ERROR: from NVidia and ATI/AMD, e.g., NVidia Quadro series or ATI Fire series. If you happen to have such a card, check\n");
			printf("PTB-ERROR: your driver settings and/or update your graphics driver.\n\n");
		}
		PsychErrMsgTxt("Frame-Sequential stereo display mode requested, but unsupported. Emulation unsupported as well. Game over!");
	}

	// Special setup code for dual window stereomode or output mode:
	if (stereomode == kPsychDualWindowStereo || (imagingmode & kPsychNeedDualWindowOutput)) {
		if (sharedContextWindow) {
			// This is creation & setup of the slave onscreen window, ie. the one
			// representing the right-eye or channel 1 view. This window doesn't do much. It
			// is not used or referenced in the users experiment script. It receives
			// its final image content during Screen('Flip') operation of the master
			// onscreen window, then gets flipped in sync with the master window.
			
			// Ok, we already have the slave window open and it shares its OpenGL context
			// with the master window. Reset its internal reference to the master:
			windowRecord->slaveWindow = NULL;
			
			// Reset imagingmode for this window prior to imaging pipeline setup. This
			// window is totally passive so it doesn't need the imaging pipeline.
			imagingmode = 0;

			// Assign this window to the master window as a slave:
			sharedContextWindow->slaveWindow = windowRecord;
			
			// Try to optionally enable framelock / swaplock extensions for the window-pair
			// if this is supported by the given system configuration. If supported, this
			// should guarantee perfect synchronization of bufferswaps across the window-pair:
			PsychOSSetupFrameLock(sharedContextWindow, windowRecord);

			// Reset master assignment to prepare possible further dual-window config operations:
			sharedContextWindow = NULL;

			// Activate the IdentitiyBlitChain for the slave window and add a single identity blit
			// operation to it: This is needed in PsychPreFlipOperations() for final copy of stimulus
			// image into this slave window:
			PsychPipelineAddBuiltinFunctionToHook(windowRecord, "IdentityBlitChain", "Builtin:IdentityBlit", INT_MAX, "");
			PsychPipelineEnableHook(windowRecord, "IdentityBlitChain");

			if (PsychPrefStateGet_Verbosity()>3) printf("PTB-INFO: Created master-slave window relationship for dual-window stereo/output display mode...\n");

			// Special config finished. The master-slave combo should work from now on...			
		}
		else {
			// This is initial setup & creation of the master onscreen window, ie. the one
			// representing the left-eye or channel 0 view and doing all the heavy work, acting as a
			// proxy for both windows.
			
			// Not much to do here. Just store its windowRecord as a reference for creation
			// of the slave window. We'll need it for that purpose...
			sharedContextWindow = windowRecord;
		}
	}

	// Set special half-width flag for window if we are either in a dual-display/dual-view stereo mode or if
	// if is requested as part of the imagingMode flag. This will cause PTB 2D drawing routines and window size
	// query routines etc. to return an effective window width or window rect only half the real width.
	if (windowRecord->stereomode==kPsychFreeFusionStereo || windowRecord->stereomode==kPsychFreeCrossFusionStereo || (imagingmode & kPsychHalfWidthWindow)) {
		windowRecord->specialflags = windowRecord->specialflags | kPsychHalfWidthWindow;
		imagingmode = imagingmode & (~kPsychHalfWidthWindow);
	}

    // Similar handling for twice-width windows: Used for certain packed-pixels (2 stimulus pixels in one fb pixel) formats:
	if (imagingmode & kPsychTwiceWidthWindow) {
		windowRecord->specialflags = windowRecord->specialflags | kPsychTwiceWidthWindow;
		imagingmode = imagingmode & (~kPsychTwiceWidthWindow);
	}

	// Similar handling for windows of half the real height, except that none of our built-in stereo modes requires these,
	// so this is only done on request from external code via the imagingmode flag kPsychHalfHeightWindow.
	// One use of this is when using interleaved line stereo mode (PsychImaging(...'InterleavedLineStereo')) where windows
	// only have a useable net height of half their physical height:
	if (imagingmode & kPsychHalfHeightWindow) {
		windowRecord->specialflags = windowRecord->specialflags | kPsychHalfHeightWindow;
		imagingmode = imagingmode & (~kPsychHalfHeightWindow);
	}

	// Define windows clientrect. It is a copy of windows rect, but stretched or compressed
    // to twice or half the width or height of the windows rect, depending on the special size
    // flags. clientrect is used as reference for all size query functions Screen('Rect'), Screen('WindowSize')
    // and for all Screen 2D drawing functions:
    PsychSetupClientRect(windowRecord);

	// Initialize internal image processing pipeline if requested:
	if (numWindowBuffers > 0) PsychInitializeImagingPipeline(windowRecord, imagingmode, multiSample);
	
	// On OS-X, if we are in quad-buffered frame sequential stereo mode, we automatically generate
	// blue-line-sync style sync lines for use with stereo shutter glasses. We don't do this
	// by default on Windows or Linux: These systems either don't have stereo capable hardware,
	// or they have some and its drivers already take care of sync signal generation.
	if (((PSYCH_SYSTEM == PSYCH_OSX) && (windowRecord->stereomode == kPsychOpenGLStereo)) || (windowRecord->stereomode == kPsychFrameSequentialStereo)) {
		if (PsychPrefStateGet_Verbosity()>3) printf("PTB-INFO: Enabling internal blue line sync renderer for quad-buffered stereo...\n");
		PsychPipelineAddBuiltinFunctionToHook(windowRecord, "LeftFinalizerBlitChain", "Builtin:RenderStereoSyncLine", INT_MAX, "");
		PsychPipelineEnableHook(windowRecord, "LeftFinalizerBlitChain");		
		PsychPipelineAddBuiltinFunctionToHook(windowRecord, "RightFinalizerBlitChain", "Builtin:RenderStereoSyncLine", INT_MAX, "");
		PsychPipelineEnableHook(windowRecord, "RightFinalizerBlitChain");		
	}

	// Activate new onscreen window for userspace drawing: If imaging pipeline is active, this
	// will bind the correct rendertargets for the first time. We soft-reset first to get
	// into a defined state:
	PsychSetDrawingTarget((PsychWindowRecordType*) 0x1);
	PsychSetDrawingTarget(windowRecord);

    // Set the clear color and perform a backbuffer-clear:
    PsychConvertColorToDoubleVector(&color, windowRecord, windowRecord->clearColor);
    PsychGLClear(windowRecord);

    // Mark end of drawing op. This is needed for single buffered drawing:
    PsychFlushGL(windowRecord);

    // Make sure no OpenGL errors happened up to this point:
    PsychTestForGLErrors();

    // If we are in logo-startup mode (former blue-screen mode) and double-buffering
    // is enabled, then do an initial bufferswap & clear, so the display starts in
    // the user selected background color instead of staying at the blue screen or
    // logo display until the Matlab script first calls 'Flip'.
    if (((PsychPrefStateGet_VisualDebugLevel()>=4) || (windowRecord->stereomode > 0)) && numWindowBuffers>=2) {
      // Do three immediate bufferswaps by an internal call to Screen('Flip'). This will also
      // take care of clearing the backbuffer in preparation of first userspace drawing
      // commands and such. We need up-to 3 calls to clear triple-buffered setups from framebuffer junk.
      PsychFlipWindowBuffers(windowRecord, 0, 0, 0, 0, &dummy1, &dummy2, &dummy3, &dummy4);
      PsychFlipWindowBuffers(windowRecord, 0, 0, 0, 0, &dummy1, &dummy2, &dummy3, &dummy4);
      PsychFlipWindowBuffers(windowRecord, 0, 0, 0, 0, &dummy1, &dummy2, &dummy3, &dummy4);
      // Display now shows background color, so user knows that PTB's 'OpenWindow'
      // procedure is successfully finished.
    }

    PsychTestForGLErrors();

    // Reset flipcounter to zero:
    windowRecord->flipCount = 0;
	
    //Return the window index and the rect argument.
    PsychCopyOutDoubleArg(1, FALSE, windowRecord->windowIndex);

    // Optionally return the windows clientrect:
    PsychCopyOutRectArg(2, FALSE, windowRecord->clientrect);

    return(PsychError_none);   
}