1. Scratch for Interactivity Dr. Ben Schafer Department of Computer Science University of Northern Iowa

2. Activity #1 – adding simple interactivity Yesterday at one point I suggested that you create a sequence of actions so that the sprite draws –A square (saved as “SquareTracer” ??) –An octagon –An equilateral triangle

3. Activity #1 – adding simple interactivity Suppose that instead I asked you to write a program that had the sprite draw an n-sided regular polygon where n was provided by the human user of our program.

4. Activity #1 – adding simple interactivity Learn about –introduce variables –introduce mathematical operations –introduce slider based interaction

5. Some challenges How do we get the input from the user? How do we tell the computer to repeat based on this answer? How do we change out side length and angles based on this answer?

6. One solution While we technically have several problems, all are solved through the introduction of a variable.

7. Thought questions What is a variable? Where do we use one in general? Where do we use one(s) in this problem?

8. Variables Select the variables menu from the script block area. Notice that by default none are provided and that there are no script blocks available. Press the Make a variable button.

9. Variables We need to give our variable a good name. In this situation we want a variable to store the number of sides on our polygon. Therefore…

10. Variables After creating a variable several script blocks appear below a list of our current variables (at this point, only one).

11. Variables Insert the “set … to … “ block at the beginning of the cat’s script and assign it’s initial value to 4

12. Variables Replace the numerical 4 in the repeat block with the sides block from the variables menu (notice it has rounded edges meaning it can be placed there)

13. Variables Run this program. What do you observe? Change the “4” to a “6” What do you observe?

14. Variables Despite the fact that we have a six in as the sides we still get a square. Although, notice the cat is in a different place. What’s going on?

15. Variables We need to adjust our angle when we change the number of sides. Should that be another variable? It could be, but there’s a better (easier) way.

16. Operators How is the amount of each turn (angle) related to the number of sides? If there is a mathematical relationship (and there is) we can use operator blocks to have the computer make the calculation.

17. Operators Notice that the Operators menu contains several mathematical (rounded edge) and boolean/logical (angle edge) blocks

18. Modifying our code We can improve our solution by replacing the “hard coded” numbers of 100 and 90 with mathematical calculations based off of the original number of sides. Try a variety of inputs. Does it seem to work?

19. Other ways to provide input? Ok, a human user SORT of has a way to change the sides, but it is pretty lame. How can we provide input during execution (“run-time”)?

20. Variable Sliders Right click on the display for “sides” Select the slider option. Test out the resulting program.

21. Slider values are too extreme Right click again on the sides display. Notice that the options have changed now that it is a slider. Select “set slider min and max” Set min=3 and max=20

22. Thoughts, comments, questions?

23. Activity #2 – A game We will make a game where the player controls a baby using the arrow keys to catch a falling ball. If the baby misses the ball the game is over.

24. Activity #2 - Goals Learn about –introduce event handling –introduce conditionals –more with loops –more with variables –more with parallel execution (yesterday) –more with message passing (yesterday)

25. Delete the Cat Click on the scissors and your cursor turns to scissors and then click on the cat to delete it Or right click on the cat and pick delete

26. Add the Baby Click on the button with the picture of folder with a star in it –if you hover over it, it says "Choose new sprite from file"

27. Select the People Folder

28. Scroll to the Baby Click on the baby and then OK

29. Resize Your Sprite! You can make your sprite larger or smaller by using the “grow sprite” or “shrink sprite” icons. You click on one of these icons, then click on your sprite until it is the size you’d like. shrink grow

30. Move the Sprite Select (click on the arrow and then on the sprite) and click and drag the sprite to the bottom of the window

31. Add a Background Click on the Stage –In the bottom right area Click on the Backgrounds tab –In the center Click on the import button Pick a background –Like bedroom1 in indoors

32. Event Handling We want to control the baby using the arrow keys –When we click the left arrow the baby should move left –When we click the right arrow the baby should move right This is a form of event handling –Responding to user actions like mouse clicks and key presses

33. The Scratch Stage The Scratch stage is 480 pixels wide and 360 pixels high. -240 240 180 -180 0,0 at the center of the stage Moving right increases the x valueMoving left decreases the x value

34. Respond to Arrow Keys Click on Control and then drag out "when space key pressed"

35. Respond to Right Arrow Click on down arrow next to space and select right arrow

36. Respond to Right Arrow Click on Motion and drag out "move 10 steps"

37. Change the move amount Click on the 10 –it will highlight in blue Type 5 and press enter

38. Respond to Arrow Keys Drag out "when space key pressed" Change "space" to "left arrow" Drag out "move 10 steps" Change it to -5 (to move left) Click on the stage and try out the left and right arrow keys –Does the sprite leave the window?

39. Paint a Ball Click on the paint brush and star –It will say "Paint new sprite" if you hover over it

40. Draw the Ball Click the circle tool –and then use the eyedropper to pick a color –and then click in the drawing area and drag to create the ball Click ok when done Circle tool and eyedropper Drawing area

41. Size the ball as desired and move it to the top Click and drag the ball to the top of the window

42. Make the Ball Fall When the green flag is clicked we want the ball to always start at the top and fall down –Click on Control –Drag out "When green flag clicked"

43. Start the Ball Click on Motion Drag out “go to x # y # “ –this will always start the ball at its current position (Scratch doesn’t automatically put it back for you).

44. Sequential Execution One block is executed after the other In order from top to bottom When the green flag is clicked –the ball will go to the specified x and y location

45. Loops We want the ball to continue to move down unless the baby catches it How do we make this happen? –We could use lots of blocks one after the other –But, that would be slow and repetitive We need a way to repeat a block or set of blocks –This is called a loop or iteration

46. Make the ball fall Click on Control –drag out "forever" Click on Motion –drag out “change y by 10” –Change it to -1 Try it out!

47. Catch the ball! If the ball touches the baby then it is caught Let's track how many balls we have caught with a score –We will increment the score each time we catch a ball

48. Variables If we are going to keep track of the score –We want something to hold the current score –And we want to be able to change the score –We want the value to change or vary This is called a variable

49. Track the score When we start the game set the score to 0 Click on Variables Click on Make a Variable Name it score

50. Set score to 0 In the ball script Drag the “forever” down Drag out "set score to 0“ Drag the “forever” back up Notice the score showing on the window

51. Conditionals We want to increase the score if the baby caught the ball –So this action will only occur only if some condition is true –This is called a conditional or an “if”

52. Conditional Statements This code means that if the user presses the Space key on the keyboard, the sprite will move 10 steps. Notice the “angle edged” block. These blocks are used to answer Boolean (true/false) questions.

53. Conditional Statements Notice the “angle edged” block. These blocks are used to answer Boolean (true/false) questions. Conditional blocks are obtained from either the Operators or the Sensing menu.

54. Sensing The sensing menu contains a number of blocks which detect whether certain situations are true (or false). In our current program we are interested in the “touching” block.

55. Did we catch the ball? From Control drag out an “if” Check if the ball is touching the baby –Get this in Sensing If this is true increment the score –From Variables

56. Increment the score Try it out! –is this what you expected? Computers do what you tell them to –Not what you want them to

57. Reset the Ball If we caught the ball –Increment the score –And move the ball to some random spot at the top of the window –So we don’t keep increasing the score

58. Reset the Ball Click on Number –drag out "pick random 1 to 10" –drop on the x value after “go to x:” –change the 1 to -235 and change 10 to 235 –change the y value to match the y in the first “go to x # y #”

59. Adding Losing If the baby doesn't catch the ball it just gets stuck at the bottom of the screen Let's tell the player that he or she lost

60. Add a text sprite Click on the Paint new sprite button –Click on the T for text –Pick the color –Modify the font size –Move the square to where you want the text –Type You Lost!

61. Hide the sprite We don’t want to tell the player that she lost when the game starts –So hide the message when the game starts Click on Control –drag out "when green flag clicked" Click on Looks –drag out “hide”

62. Check if Lost If the y position gets near the bottom (near -180) –Drag out an if from Control –Drag out a blank < blank From Numbers –Add a y position From Motion –Type in -175

63. Broadcast a message Sprites communicate by passing messages –One sprite broadcasts the message –Other sprites can listen for it and react to it when they receive it –Click on Control drag out "broadcast blank" click on the drop down arrow next to new – name it lost Add “stop script” –to stop the forever loop Sprites communicate by passing messages –One sprite broadcasts the message –Other sprites can listen for it and react to it when they receive it –Click on Control drag out "broadcast blank" click on the drop down arrow next to new – name it lost Add “stop script” –to stop the forever loop

64. Receive Lost Click on the text sprite Click on Control –drag out "when I receive blank" –click on the down arrow and select lost Click on Looks –drag out “show” Click on Control –drag out “stop all” to stop all scripts

65. Parallel Execution We have several things happening at the same time –when the green flag is clicked This is called parallel execution –More than one thing happening at a time

66. Create Instructions Click on the Show Project Notes icon in the upper right corner Add the instructions Press OK

67. Test your game Click the green flag If you want, adjust the speed of the ball –Increase the amount it changes in y Modify the sprites using the “Costume” tab Save your game with the “Save” button

68. Other Ideas Add a sound when you lose Add the ability to win –When you reach a certain score –Track the amount of time it takes as well Speed up the ball over time Add more sprites to catch Add a sprite to avoid (like a big brother) –killer sprite

69. Concept Summary The Variables menu –can hold values and can change value The Sensing menu –Can be used to see if certain conditions exist Forever loops –repeat all the commands inside of them one at a time until the script is stopped or all scripts are stopped Conditionals – ifs –only execute the body of the if when the condition is true –Sometimes used with sensing blocks

70. Concept Summary Sprites can pass messages –and receive them Sprites can react to events –like clicking the green flag and pressing the left or right arrow keys Sprites can have several scripts, costumes, and sounds Things can happen one after the other – sequential execution or at the same time – parallel execution