function AlphaImageTutorial
% AlphaImageTutorial
%
% Display a gaussian masked image, locked to the cursor position,
% using the Screen('DrawTexture') command.
%
% This illustrates an application of OpenGL Alpha blending by displaying
% an image masked with a gaussian transparency mask.
%
% In each frame, first the image is drawn. Then a texture acting as a
% transparency mask is drawn "over" the image, leaving only selected
% parts of the image.
%
% Please note that we only use two textures: One holding the image,
% the other defining the mask.
%
% see also: PsychDemos, MovieDemo, DriftDemo

% HISTORY
%
% mm/dd/yy
%
%  6/28/04    awi     Adapted from Denis Pelli's DriftDemo.m for OS 9
%  7/18/04    awi     Added Priority call.  Fixed.
%  9/8/04     awi     Added Try/Catch, cosmetic changes to comments and see also.
%  1/4/05     mk      Adapted from awi's DriftDemoOSX.
%  24/1/05    fwc     Adapted from AlphaImageDriftDemoOSX, bug in
%                     drawtexture prevents it from doing what I really want
%  28/1/05    fwc     Yeah, works great now after bug was removed from
%                     drawtexture by mk, cleaned up code
%  02/07/05   fwc     slightly simplified demo by removing some options
%                       such as automode
%  3/30/05    awi     Added 'BlendFunction' call to set alpha blending mode
%                     The default alpha blending mode for Screen has
%                     changed, this added call sets it to the previous
%                     default.
%  4/23/05    mk      Small modifications to make it compatible with
%                     "normal" Screen.mexmac.
%  12/31/05   mk      Small modifications to make it compatible with Matlab-5
%  10/14/06   dhb     Rename without OSX bit.  Fewer warnings.
%             dhb     More comments, cleaned.

% PsychDefaultSetup(featurelevel) - Perform standard setup for Psychtoolbox, 
% the feature level of 2 sets PTB up to use an unclamped 0 - 1 color range.
PsychDefaultSetup(2);

% Screen is able to do a lot of configuration and performance checks on
% open, and will print out a fair amount of detailed information when
% it does.  These commands supress that checking behavior and just let
% the demo go straight into action.  See ScreenTest for an example of
% how to do detailed checking.
oldVisualDebugLevel = Screen('Preference', 'VisualDebugLevel', 3);
oldSupressAllWarnings = Screen('Preference', 'SuppressAllWarnings', 1);
oldSkipSyncTests = Screen('Preference', 'SkipSyncTests', 2);

% Standard coding practice, use try/catch to allow cleanup on error.
try
	% Say hello in command window
	fprintf('\nAlphaImageDemo\n');
	
	% Get the list of screens and choose the one with the highest screen number.
	% Screen 0 is, by definition, the display with the menu bar. Often when
	% two monitors are connected the one without the menu bar is used as
	% the stimulus display.  Chosing the display with the highest dislay number is
	% a best guess about where you want the stimulus displayed.
	screenNumber=max(Screen('Screens'));
	
	% Open a double buffered fullscreen window and draw a gray background
	% and front and back buffers.
	[w, wRect]=PsychImaging('OpenWindow',screenNumber, 0.5, [], 32, 2);
	
	%This is our alpha blending mode
	Screen(w,'BlendFunction',GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
	
	% Find the color values which correspond to white, gray and black.
	black=BlackIndex(w);
	gray=GrayIndex(w);
	white=WhiteIndex(w);
	
	% Import image and and convert it, stored in
	% MATLAB matrix, into a Psychtoolbox OpenGL texture using 'MakeTexture';
	myimgfile = [ PsychtoolboxRoot 'PsychDemos' filesep 'AlphaImageDemo' filesep 'konijntjes1024x768.jpg'];
	fprintf('Using image ''%s''\n', myimgfile);
	imdata=imread(myimgfile);
	
	% Crop image if it is larger then screen size. There's no image scaling
	% in maketexture
	[iy, ix, iz]=size(imdata); %#ok<NASGU>
	[wW, wH]=WindowSize(w);
	if ix>wW || iy>wH
		fprintf('Image size exceeds screen size\n');
		fprintf('Image will be cropped\n');
	end
	if ix>wW
		cl=round((ix-wW)/2);
		cr=(ix-wW)-cl;
	else
		cl=0;
		cr=0;
	end
	if iy>wH
		ct=round((iy-wH)/2);
		cb=(iy-wH)-ct;
	else
		ct=0;
		cb=0;
	end
	
	% Set up texture and rects
	imagetex=Screen('MakeTexture', w, imdata(1+ct:iy-cb, 1+cl:ix-cr,:));
	tRect=Screen('Rect', imagetex);
	[ctRect, dx, dy]=CenterRect(tRect, wRect);
	
	% We create a Luminance+Alpha matrix for use as transparency mask:
	% Layer 1 (Luminance) is filled with luminance value 'gray' of the
	% background.
	ms = 100;
	transLayer = 2;
	[x,y] = meshgrid(-ms:ms, -ms:ms);
	maskblob = ones(2*ms+1, 2*ms+1, transLayer) * gray;
	size(maskblob);
	
	% Layer 2 (Transparency aka Alpha) is filled with gaussian transparency
	% mask.
	xsd = ms/2.0;
	ysd = ms/2.0;
	maskblob(:,:,transLayer)= white - exp(-((x/xsd).^2)-((y/ysd).^2))*white;
	
	% Build a single transparency mask texture
	masktex=Screen('MakeTexture', w, maskblob);
	mRect=Screen('Rect', masktex);
	fprintf('Size image texture: %d x %d\n', RectWidth(tRect), RectHeight(tRect));
	fprintf('Size  mask texture: %d x %d\n', RectWidth(mRect), RectHeight(mRect));
	
	% Blank sceen
	Screen('FillRect',w, gray);
	Screen('Flip', w);
	
	% initialize mouse position at center
	[a,b]=WindowCenter(w);
	SetMouse(a,b,screenNumber);
	HideCursor;
	
	% Bump priority for speed
	priorityLevel=MaxPriority(w);
	Priority(priorityLevel);
	
	% Pre-load textures
	Screen('DrawTexture', w, imagetex);
	Screen('DrawTexture', w, masktex);
	Screen('FillRect',w, gray);
	Screen('Flip', w);
	
	mode = 0;
	
	% Main mouse tracking loop
	mxold=0;
	myold=0;
	while (1)
		% We wait at least 10 ms each loop-iteration so that we
		% don't overload the system in realtime-priority:
		WaitSecs(0.01);
		
		% We only redraw if mouse has been moved:
		[mx, my, buttons]=GetMouse(screenNumber);
		if (mx~=mxold || my~=myold)
			myrect=[mx-ms my-ms mx+ms+1 my+ms+1]; % center dRect on current mouseposition
			dRect = ClipRect(myrect,ctRect);
			sRect=OffsetRect(dRect, -dx, -dy);
			
			if ~IsEmptyRect(dRect)
				
				if mode == 0
					% Draw whole image:
					Screen('DrawTexture', w, imagetex);
					% Useful info for user about how to quit.
					Screen('DrawText', w, 'No mask Visible.  Click mouse to begin...', 20, 20, black);
				end
				
				if mode == 1
					% Draw whole image:
					Screen('DrawTexture', w, imagetex);
					
					% Draw selected aperture rectangle:
					Screen('FillRect', w, [1 0 0 0.25], dRect);
					% Useful info for user about how to quit.
					Screen('DrawText', w, 'Red FillRect with 0.25 alpha.  Click mouse for next mode...', 20, 20, black);
				end
				
				if mode >= 2
					% Draw image for current frame:
					Screen('DrawTexture', w, imagetex, sRect, dRect);
					if mode==2;Screen('DrawText', w, 'No mask, just destination rect.  Click mouse for next mode...', 20, 20, black);end
				end
				
				if mode == 3
					% Overdraw -- and therefore alpha-blend -- with gaussian alpha mask
					Screen('DrawTexture', w, masktex, [], myrect);
					% Useful info for user about how to quit.
					Screen('DrawText', w, 'Gaussian mask.  Click mouse to exit...', 20, 20, black);
				end
							
				% Show result on screen:
				Screen('Flip', w);
			end
		end
		mxold=mx;
		myold=my;
		
		% Break out of loop on mouse click
		if find(buttons)
			while any(buttons)
				[mx, my, buttons]=GetMouse(screenNumber);
			end
			
			mode = mode + 1;
			
			if mode == 4
				break;
			end
		end
	end
	
	% The same command which closes onscreen and offscreen windows also
	% closes textures.
	sca;
	ShowCursor;
	Priority(0);
	
	% Restore preferences
	Screen('Preference', 'VisualDebugLevel', oldVisualDebugLevel);
	Screen('Preference', 'SuppressAllWarnings', oldSupressAllWarnings);
	Screen('Preference', 'SkipSyncTests', oldSkipSyncTests);
	
	% This "catch" section executes in case of an error in the "try" section
	% above.  Importantly, it closes the onscreen window if it's open.
catch
	
	sca;
	ShowCursor;
	Priority(0);
	
	% Restore preferences
	Screen('Preference', 'VisualDebugLevel', oldVisualDebugLevel);
	Screen('Preference', 'SuppressAllWarnings', oldSupressAllWarnings);
	Screen('Preference', 'SkipSyncTests', oldSkipSyncTests);

	psychrethrow(psychlasterror);
end