Matlab Class 6 Xiaotao Su, Ph.D. Visual Psychophysicist

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

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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)

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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//audac
ity.sourceforge.net/
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Getting Input from the Mouse

• mouse_x, mouse_y, buttons GetMouse(window_ptr)
  
• Hide and show the windows cursor during a
  simulationHideCursor, ShowCursor
• If sum(buttons)gt0, a button has been clicked

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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 circleScreen(window, 'FillOval',
  dot_color, circle_rect)
• The position of the cursor marks the center of
  the circle and the rectangle it is inscribed in.

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• mousingAround.m
• clear all
• try
• which_screen0
• 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(toclt5) mouse_x, mouse_y, buttons
GetMouse if(sum(buttons)gt0) dot_color
red else dot_color green end cursor
mouse_x-dot_r, mouse_y-dot_r, ...
mouse_xdot_r, mouse_ydot_r Screen(window_pt
r, 'FillOval', dot_color, cursor) Screen('Flip',
window_ptr) end clear Screen ShowCursor catch
clear Screen ShowCursor end
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Direction/Velocity Vectors

• A vector has both magnitude and direction
• Direction x,y
• Magnitude v v(x2y2) sqrt(x2 y2)
  Pythagorean

x
v
y
x
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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) lt
  screen_dimensions(2)
• Collision w/ left border if rect1(1) lt
  screen_dimensions(1)
• Collision w/ bottom border if rect1(4) gt
  screen_dimensions(4)
• Collision w/ right border if rect1(3) gt
  screen_dimensions(2)

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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

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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_xgtshape_rect(1))...
• (mouse_xltshape_rect(3))...
• (mouse_ygtshape_rect(2))...
• (mouse_yltshape_rect(4)))
• shape_color purple
• end