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)

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]);

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]);

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 http://audacity.sourceforge.net/

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

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.

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

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

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)

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

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