1. Matlab Class 6 Xiaotao Su, Ph. D
Matlab Class 6 Xiaotao Su, Ph.D. Visual Psychophysicist & IT Group Leader & Hristiyan Kourtev Rutgers Center for Cognitive Science (RuCCS)

2. Displaying images on screen w/ PTB
img = imread(‘winter.jpg’, ‘jpg’);
You draw an image just like you would a rectangle:
Screen(window, ‘PutImage’, img, [0, 0, 200, 200]);

3. Image info and structures
img_info = imfinfo(‘winter.jpg’)
img_info.Width will be the width of the image
screen(window, ‘PutImage’, img,
[0, 0, img_info.Width, img_info.Height]);

4. Making/Playing sounds w/ PTB
A sound is a 2 x N matrix where N is the number of bits that make up the sound file and the two channels are for left and right
[sound, samplerate, samplesize] =
wavread(‘feedback.wav’);
sound = sound’;
Snd(‘Play’, sound, samplerate, samplesize);
Tip:
To make your own wav files I recommend
using an application called audacity

5. Getting Input from the Mouse
[mouse_x, mouse_y, buttons] = GetMouse(window_ptr);
Hide and show the windows cursor during a simulation: HideCursor, ShowCursor
If sum(buttons)>0, a button has been clicked

6. Task 1 – Mousing Around
Draw a green circle of radius 30 pixels, whose location on the screen is controlled by the mouse
Change the color of the circle to red when a button is clicked and back to green when released
Hints: You will need to use the following functions
Draw a circle: Screen(window, 'FillOval', dot_color, circle_rect);
The position of the cursor marks the center of the circle and the rectangle it is inscribed in.

7. dot_r = 20; %radius of cursor HideCursor; green = [0, 255, 0];
% mousingAround.m
clear all;
try
which_screen=0;
bg_color = [0, 0, 0];
[window_ptr, screen_dimensions]= …
Screen(which_screen, … 'OpenWindow', bg_color);
dot_r = 20; %radius of cursor
HideCursor;
green = [0, 255, 0];
red = [255,0, 0];
tic;
while(toc<5)
[mouse_x, mouse_y, buttons] = GetMouse;
if(sum(buttons)>0)
dot_color = red;
else
dot_color = green;
end
cursor = [ mouse_x-dot_r, mouse_y-dot_r, ...
mouse_x+dot_r, mouse_y+dot_r];
Screen(window_ptr, 'FillOval', dot_color, cursor);
Screen('Flip', window_ptr);
clear Screen;
ShowCursor;
catch

8. Direction/Velocity Vectors
A vector has both magnitude and direction
Direction = [x,y]
Magnitude = v = √(x2+y2) = sqrt(x^2 + y^2) % Pythagorean x v y x

9. Detecting Collisions With Borders
rect1 = [10, 10, 50, 50]; % [x1, y1, x2, y2]
screen_dimensions = [0, 0, 1280, 1024];
Collision w/ top border if: rect1(2) <= screen_dimensions(2)
Collision w/ left border if: rect1(1) <= screen_dimensions(1)
Collision w/ bottom border if: rect1(4) >= screen_dimensions(4)
Collision w/ right border if: rect1(3) >= screen_dimensions(2)

10. Task 2 – Bouncing off the walls
Modify your existing program to add 2 blue squares that start off in a random direction at speed 5 and 7 pixels respectively and bounce off the walls
Hints:
Will need to use the Pythagorean theorem to calculate the direction vectors making sure the magnitude is as specified
If a square bumps into the left or right walls, invert (multiply by -1) the x component of its velocity vector
If a square bumps into the top or bottom walls, invert (multiply by -1) the y component of its velocity vector

11. Task 3 – Click, Click Modify your program to:
Add a circular cursor controlled by the mouse
Make the squares clickable. They should change color to purple when clicked.
Hint: Purple = [255,0,255];
Hint: The cursor is inside the square if:
if((mouse_x>shape_rect(1))&...
(mouse_x<shape_rect(3))&...
(mouse_y>shape_rect(2))&...
(mouse_y<shape_rect(4)))
shape_color = purple;
end