function DriftDemo
% DriftDemo
% ___________________________________________________________________
%
% Display an animated grating using the new Screen('DrawTexture') command.
% In Psychtoolbox-3 Screen('DrawTexture') replaces
% Screen('CopyWindow').
%
% This is a very simple, bare bones demo on how to do frame animation. For
% much more efficient ways to draw gratings and gabors, have a look at
% DriftDemo2, DriftDemo3, DriftDemo4, ProceduralGaborDemo, GarboriumDemo,
% ProceduralGarboriumDemo and DriftWaitDemo.
%
% CopyWindow vs. DrawTexture:
%
% In the OS 9 Psychtoolbox, Screen ('CopyWindow") was used for all
% time-critical display of images, in particular for display of the movie
% frames in animated stimuli. In contrast, Screen('DrawTexture') should not
% be used for display of all graphic elements, but only for display of
% MATLAB matrices. For all other graphical elements, such as lines, rectangles,
% and ovals we recommend that these be drawn directly to the  display
% window during the animation rather than rendered to offscreen windows
% prior to the animation.
% _________________________________________________________________________
%
% see also: PsychDemos, MovieDemo

% HISTORY
%  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.
%  4/23/05    mk      Added Priority(0) in catch section, moved Screen('OpenWindow')
%                     before first call to Screen('MakeTexture') in
%                     preparation of future improvements to 'MakeTexture'.
%  2/28/09    mk      Smallish refinements, cleanups, updated comments.

try
    % This script calls Psychtoolbox commands available only in OpenGL-based
    % versions of the Psychtoolbox. (So far, the OS X Psychtoolbox is the
    % only OpenGL-base Psychtoolbox.)  The Psychtoolbox command AssertPsychOpenGL will issue
    % an error message if someone tries to execute this script on a computer without
    % an OpenGL Psychtoolbox.
    AssertOpenGL;

    % 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.
    screens=Screen('Screens');
    screenNumber=max(screens);

      % Find the color values which correspond to white and black: Usually
    % black is always 0 and white 255, but this rule is not true if one of
    % the high precision framebuffer modes is enabled via the
    % PsychImaging() commmand, so we query the true values via the
    % functions WhiteIndex and BlackIndex:
    white=WhiteIndex(screenNumber);
    black=BlackIndex(screenNumber);

    % Round gray to integral number, to avoid roundoff artifacts with some
    % graphics cards:
    gray=round((white+black)/2);

    % This makes sure that on floating point framebuffers we still get a
    % well defined gray. It isn't strictly neccessary in this demo:
    if gray == white
        gray=white / 2;
    end

    % Contrast 'inc'rement range for given white and gray values:
    inc=white-gray;

    % Open a double buffered fullscreen window and select a gray background
    % color:
    w=Screen('OpenWindow',screenNumber, gray);

    % Compute each frame of the movie and convert the those frames, stored in
    % MATLAB matices, into Psychtoolbox OpenGL textures using 'MakeTexture';
    numFrames=12; % temporal period, in frames, of the drifting grating
    for i=1:numFrames
        phase=(i/numFrames)*2*pi;
        % grating
        [x,y]=meshgrid(-300:300,-300:300);
        angle=30*pi/180; % 30 deg orientation.
        f=0.05*2*pi; % cycles/pixel
        a=cos(angle)*f;
        b=sin(angle)*f;
        m=exp(-((x/90).^2)-((y/90).^2)).*sin(a*x+b*y+phase);
        tex(i)=Screen('MakeTexture', w, round(gray+inc*m)); %#ok<AGROW>
    end

    % Run the movie animation for a fixed period.
    movieDurationSecs=5;
    frameRate=Screen('FrameRate',screenNumber);

    % If MacOSX does not know the frame rate the 'FrameRate' will return 0.
    % That usually means we run on a flat panel with 60 Hz fixed refresh
    % rate:
    if frameRate == 0
        frameRate=60;
    end

    % Convert movieDuration in seconds to duration in frames to draw:
    movieDurationFrames=round(movieDurationSecs * frameRate);
    movieFrameIndices=mod(0:(movieDurationFrames-1), numFrames) + 1;

    % Use realtime priority for better timing precision:
    priorityLevel=MaxPriority(w);
    Priority(priorityLevel);

    % Animation loop:
    for i=1:movieDurationFrames
        % Draw image:
        Screen('DrawTexture', w, tex(movieFrameIndices(i)));
        % Show it at next display vertical retrace. Please check DriftDemo2
        % and later, as well as DriftWaitDemo for much better approaches to
        % guarantee a robust and constant animation display timing! This is
        % very basic and not best practice!
        Screen('Flip', w);
    end

    Priority(0);

    % Close all textures. This is not strictly needed, as
    % Screen('CloseAll') would do it anyway. However, it avoids warnings by
    % Psychtoolbox about unclosed textures. The warnings trigger if more
    % than 10 textures are open at invocation of Screen('CloseAll') and we
    % have 12 textues here:
    Screen('Close');

    % Close window:
    sca;

catch
    %this "catch" section executes in case of an error in the "try" section
    %above.  Importantly, it closes the onscreen window if its open.
    sca;
    Priority(0);
    psychrethrow(psychlasterror);
end %try..catch..