Keith Schneider, 17 August 2006 Matlab and Psychophysics Toolbox Seminar
Part 5. Animation II
Rotations
One of the parameters in the Screen('DrawTexture') that we haven’t utilized yet is the rotation parameter. The video hardware can quickly rotate, translate and resize any image, and the function takes advantage of that. Here’s an example of a spinning image (you can try this out with red/green 3D glass if you have them to experience binocular rivalry).
% rotating binocular rivalry stimulus
% Key press start rotation, stop rotation and exit.
潘基文是哪国人% Wear red/green glass and fixate at the center.
cycles = 20; % spatial frequency (cycles per stimulus)
period = 1; % rotation period (c)
[w, rect] = Screen('OpenWindow', 0, [0 0 0]);
hidecursor;
xc = rect(3)/2; % coordinates of screen center
yc = rect(4)/2;
% make stimulus image
xysize = rect(4);
xylim = 2*pi*cycles;
熟石灰化学式[x,y] = meshgrid(-xylim:2*xylim/(xysize-1):xylim, ...
-xylim:2*xylim/(xysize-1):xylim);
img = zeros(xysize,xysize,3);
circle = x.^2 + y.^2 <= xylim^2; % circular boundry
img(:,:,1) = (sin(x)+1)/2*255 .* circle; % red channel
img(:,:,2) = (sin(y)+1)/2*255 .* circle; % green channel
t = Screen('MakeTexture', w, img);
Screen('DrawTexture', w, t);
Screen('FillOval',w,[255 255 255],[xc-4 yc-4 xc+4 yc+4]); %fixation pt. Screen('Flip', w);
KbWait;
while KbCheck; end% make sure all keys are relead
% animation loop
keyisdown = 0;
start_time = GetSecs;
while (~keyisdown)
th = mod(360*(GetSecs-start_time)/period,360); % rotation angle
Screen('DrawTexture', w, t, [], [], th);
Screen('FillOval', w, [255 255 255], [xc-4 yc-4 xc+4 yc+4]);
Screen('Flip', w);
keyisdown = KbCheck;
end
while KbCheck; end
KbWait;
ShowCursor;
Screen('Clo',w);
Next we will modify the script we wrote last week to move an image with the mou. Today we will add in image rotations controlled by the left- and right-arrow keys.
img=imread('myimage.jpg');
[yimg,ximg,z]=size(img);
rot_spd = 10; % rotation speed (degrees per frame)
larrow = KbName('LeftArrow'); % modify this for Windows? rarrow = KbName('RightArrow');
[w,rect]=Screen('OpenWindow',0,[0 0 0]);
sx = 400; % desired x-size of image (pixels)
sy = yimg*sx/ximg; % desired y-size--keep proportional
t = Screen('MakeTexture',w,img);
bdown=0;
th = 0; % initial rotation angle (degrees)
HideCursor
while(~any(bdown)) % exit loop if mou button is presd [x,y,bdown]=GetMou;
[keyisdown,cs,keycode] = KbCheck;
if(keycode(larrow))
th = th - rot_spd; % rotate counterclockwi end
if(keycode(rarrow))
th = th + rot_spd; % rotate clockwi
end
destrect=[x-sx/2,y-sy/2,x+sx/2,y+sy/2];
Screen('DrawTexture',w,t,[],destrect,th);
Screen('Flip',w);
end
Screen('Clo',w)
ShowCursor
Flickering checkerboard
Flickering checkerboard stimuli are commonly ud in fMRI experiments to map the visual field. In the following example, the flickering is accomplished by rapidly switching between two complementary images. Also, the apparent rotation of the hemifield stimulus is accomplished by first drawing the fullfield circular stimulus and then drawing a polygon with the background color on top of it to mask half. For a real experiment you would want to add in a fixation point and specify a fixed duration, rather than exiting upon a key press. The most complicated part of this program is the math ud to generate the stimulus pattern. The image checks that is created contains three values, one corresponding to the background color, and one each for the black and white checkers.
% rotating hemifield flickering checkerboard
rcycles = 8; % number of white/black circle pairs
tcycles = 24; % number of white/black angular gment pairs (integer) flicker_freq = 4; % full cycle f
licker frequency (Hz)
flick_dur = 1/flicker_freq/2;
period = 30; % rotation period (c)苗娟
[w, rect] = SCREEN('OpenWindow', 0, 128);
HideCursor
xc = rect(3)/2;
yc = rect(4)/2;
% make stimulus
hi_index=255;
关山阻隔lo_index=0;
bg_index =128;
xysize = rect(4);
s = xysize/sqrt(2); % size ud for mask
xylim = 2*pi*rcycles;
[x,y] = meshgrid(-xylim:2*xylim/(xysize-1):xylim, - ...
xylim:2*xylim/(xysize-1):xylim);
at = atan2(y,x);
checks = ((1+sign(sin(at*tcycles)+eps) .* ...
sign(sin(sqrt(x.^2+y.^2))))/2) * (hi_index-lo_index) + lo_index;
circle = x.^2 + y.^2 <= xylim^2;
checks = circle .* checks + bg_index * ~circle;
t(1) = SCREEN('MakeTexture', w, checks);
t(2) = SCREEN('MakeTexture', w, hi_index - checks); % reverd contrast flick = 1;
flick_time = 0;
start_time = GetSecs;
while (1) % animation loop
村级thetime = GetSecs - start_time; % time (c) since loop started if thetime > flick_time % time to rever contrast?
flick_time = flick_time + flick_dur; % t next flicker time
flick = 3 - flick;
end
SCREEN('DrawTexture', w, t(flick));
% draw mask
theta = 2*pi * mod(thetime, period)/period;
st = sin(theta);
ct = cos(theta);
xy = s * [-st,-ct; -st-ct,st-ct; st-ct,st+ct; st,ct] + ...
ones(4,1) * [xc yc];
Screen('FillPoly', w, bg_index, xy);
SCREEN('Flip', w);
if KbCheck
break% exit loop upon key press
end
end
ShowCursor
SCREEN('Clo',w);
Movies
Another type of animation is a movie. A movie is an animation in which you have pre-computed all of the frames of the animation, storing them in quence into memory using the Screen('MakeTexture') function. The frames can then be played, one frame per screen refresh, using the Screen('DrawTexture') function. A movie animation needs to be ud when you have imported the images you want to display, or the computer is too slow to generate them on the fly.
For example, let’s modify our mou moving and rotating script to display a random dynamic noi stimulus.
nframes = 100; % number of frames in movie
心电图检查什么s=200; % size of square (pixels)
rot_spd = 10; % rotation speed (degrees per frame)
larrow = KbName('LeftArrow'); % modified this for Windows? rarrow = KbName('RightArrow');
[w,rect]=Screen('OpenWindow',0,[0 0 0]);
% compute movie frames
t = zeros(1,nframes);
for i=1:nframes
img=255*rand(s,s,3); % colored noi image
t(i)=Screen('MakeTexture',w,img);
end
i=0;
bdown=0;
th = 0; % initial rotation angle
while(~any(bdown)) % exit loop if mou button is presd
[x,y,bdown]=GetMou;
[keyisdown,cs,keycode] = KbCheck;
if(keycode(larrow))
th = th - rot_spd; % rotate counterclockwi end
if(keycode(rarrow))
th = th + rot_spd; % rotate clockwi
end
destrect=[x-s/2,y-s/2,x+s/2,y+s/2];
i=mod(i,nframes)+1; % cycle through frames
Screen('DrawTexture', w, t(i), [], destrect, th)
Screen('Flip', w);
方的成语end
Screen('Clo',w)
You can also import your own movies. This next example may tax your video card. On Macs the movie playback functions utilize QuickTime. U your own movie or I can supply one.
% translate and rotate movie during playback
rot_spd = 10; % rotation speed (degrees per frame)
larrow = KbName('LeftArrow'); % modify for Windows?
rarrow = KbName('RightArrow');
[w,rect]=Screen('OpenWindow',0,[0 0 0]);
[m dur fps sx sy] = Screen('OpenMovie', w, 'v'); f=0;
bdown=0;
th = 0; % initial rotation angle
Screen('PlayMovie', m, 1, 1); % start movie playback
while(~any(bdown)) % exit loop if mou button is presd [x,y,bdown]=GetMou;
[keyisdown,cs,keycode] = KbCheck;
if(keycode(larrow))
th = th - rot_spd; % rotate counterclockwi end
if(keycode(rarrow))
th = th + rot_spd; % rotate clockwi
end
destrect=[x-sx/2,y-sy/2,x+sx/2,y+sy/2];
t = Screen('GetMovieImage', w, m, 1); % grab frame
Screen('DrawTexture',w,t,[],destrect,th)
Screen('Flip',w);
end
Screen('CloMovie', m);
Screen('Clo',w)
The way this script works is to grab the current frame into a texture using the
Screen('GetMovieImage') function. This texture can then be quickly rotated, translated, resized, etc. You could make the movie bounce around, play multiple instances of the movie by drawing the texture in different locations, etc.
As you can e, the Psychophysics Toolbox is quite powerful. For more examples in changing the movie playback rate, rewinding the movie, and so on, e PlayMoviesDemoOSX.m and related demos in the
Psychtoolbox/PsychDemos/QuickTimeDemos directory, or read the help files for the Screen('OpenMovie') and Screen('PlayMovie') functions.
Dot fields
If you want to display a field containing a large number of moving dots, you may find that the Screen('FillOval') is too slow to draw a sufficiently high density of dots each frame. For this purpo, u the Screen('DrawDots') function. Let’s modify our translating and rotating script to display a field of moving dots:
dot_speed = 10; % dot speed (pixels/frame)
ndots = 500; % number of dots
dot_w = 10; % width of dot (pixels)
s = 500; % field size (pixels)
rot_spd = 2; % rotation speed (degrees per frame)
larrow = KbName('LeftArrow'); % modify for Windows?
rarrow = KbName('RightArrow');
x = s * rand(1,ndots); % initial position
y = s * rand(1,ndots);
w=Screen('OpenWindow',0,0);
Priority(MaxPriority(w));
% Enable alpha blending for smoothed points:简单辞职报告
Screen('BlendFunction', w, GL_SRC_ALPHA, ...
GL_ONE_MINUS_SRC_ALPHA);
bdown=0;
th = 0; % initial heading
HideCursor
while(~any(bdown)) % exit loop if mou button is presd
[mx,my,bdown]=GetMou;
[keyisdown,cs,keycode] = KbCheck;
if(keycode(larrow))
th = th - rot_spd; %rotate heading counterclockwi end
if(keycode(rarrow))
th = th + rot_spd; %rotate heading clockwi end
dx = dot_speed * cos(th*pi/180); % x-velocity
dy = dot_speed * sin(th*pi/180); % y-velocity
x = mod(x+dx,s); % update positions, looping at edges
y = mod(y+dy,s);
Screen('DrawDots',w,[x;y], dot_w, 255, [mx my]-s/2, 1); Screen('Flip',w);
end
Screen('Clo',w)
ShowCursor
Priority(0);
Also, e the DotDemo.m program for an example with multiple dot sizes and colors. If your video card doesn’t support alpha blending, you will e square dots instead of circular ones.
