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Text me

Learn It

  • Almost all games require text to be displayed on the screen.
  • It would be handy to make something we can use again and again without writing the code repeatedly.
  • In computing this is called a function. It is an independent block of code that lives outside the main program and only runs when asked to do so by the main program.
  • Functions definitions always sit at the top of the code after the import statements.

Try It

  • Let's start by writing a simple program, and looking at how we can adapt it to to use functions.
  • What if we wanted a program to multiply some numbers together?
  • Our pseudocode could be something like this:
keepGoing = True
WHILE keepGoing == True:
   firstNumber = INPUT "What number would you like? "
   secondNumber = INPUT "What number to multiply it by? "
   result = firstNumber * secondNumber
   print "The answer is " + result

   yourAnswer = input "Again? "
   IF yourAnswer = "no" THEN
      keepGoing = False
   ENDIF
END WHILE
  • In this program, the WHILE loop has a lot of lines of code in it.
  • It'd be a lot easier to read the code if there were less of it.
  • Let's make some functions to clean this up. Our code could instead say:
  • NOTE: Line numbers are shown to make this easier to discuss.
1 FUNCTION getNumbers()
2    num1 = INPUT "What number would you like? "
3    num2 = INPUT "What number to multiply it by? "
4 RETURN num1, num2
5
6 FUNCTION doTheMaths(a, b)
7    theAnswer = a * b
8 RETURN theAnswer
9 
10 ''' THE ACTUAL PROGRAM STARTS HERE '''
11 keepGoing = True
12 WHILE keepGoing == True
13    firstNumber, secondNumber = getNumbers()
14    result = doTheMaths (firstNumber, secondNumber)
15    print "The answer is " + result
16
17    yourAnswer = input "Again? "
18    IF yourAnswer = "no" THEN
19       keepGoing = False
20    ENDIF
21 END WHILE
  • The the program runs, the two functions at the very top (lines 1-8) are read by the computer, but not used.
  • In effect, we are teaching the computer two new sets of code that we will eventually ask it to run when desired. The first line of code carried out is on line 11 (line 10 is a comment).
  • Pro tip: When you ask the computer to run a function, we use the term calling.
  • On line 13, the program calls the getNumbers() function. The program then runs the code on lines 1-4.
  • The result of running that function is two numbers entered by the user, and stored in variables called num1 and num2.
  • When line 4 of the code is run, the values entered by the user are returned to where we were in the program before the function was called (line 13). The values are stored in firstNumber and secondNumber.
  • The same process is repeated on line 14, but this time the numbers to be calculated are sent along when the doTheMaths() function is called.
  • Here's the Python code to accomplish this task:
def getNumbers():
    num1 = int(input("What number would you like? "))
    num2 = int(input("What number to multiply it by? "))
    return num1, num2

def doTheMaths(a, b):
    theAnswer = a * b
    return theAnswer


''' THE ACTUAL PROGRAM STARTS HERE '''
keepGoing = True
while keepGoing == True:
    firstNumber, secondNumber = getNumbers()
    result = doTheMaths (firstNumber, secondNumber)
    print("The answer is " + str(result))

    yourAnswer = input("Again? ")
    if yourAnswer == "no":
	keepGoing = False
  • Put the code into a new, empty Python file, save it and run it.
  • Challenge: Could you add a function to replace the last 3 lines of the program (seeing if the user wishes to play again) with 1 line?
  • If you're struggling with the concept of functions the task above is explained in the tutorial below:

Download It

Try It

  • We're going to create a function to allow us to draw text onto the screen.
  • Our pseudocode to do this is as follows:
''' Setup code - run once only '''
fontName = Load 'Arial' font into memory

FUNCTION textDraw(msgText)
    font = Use fontName, make the size 22.
    text_surface = Use msgText as the message, and colour it white
    blit the screen, drawing text_surface at coordinates: 100, 100.
END FUNCTION

''' GAME LOOP CODE - run repeatedly '''
CALL textDraw("Good morning, Dave")
  • To code this in Python, first we need to load a font from the PC's font collection and store it in a variable for later use. Add this line just above the game loop (around line 18).
fontName = pygame.font.match_font('arial')
  • It should look like this:

7-1.png

  • Write the code for our function next, adding this code at the top of the program, immediately underneath the import statements near line 4.
def textDraw(msgText):
    font = pygame.font.Font(fontName, 22)
    text_surface = font.render(msgText, True, white)
    screen.blit(text_surface, (100, 100))
  • It'll look like this:
  • NOTE: Make sure you indent your code like in the screenshot above, or this won't work.

7-2.png

  • Now we've taught the computer how to write text, we can call this function any time we want to write something.
  • Add a function call inside the game loop, by adding this code:
textDraw("Good morning, Dave")
  • It'll look like this:
  • NOTE: Again, ensure that you've indented the code.

7-3.png

Program It

  • It would be even more useful if we could tell the textDraw function which X, Y coordinates we’d like the text to be shown at. At the moment, we're always drawing at 100, 100.
  • We can accomplish this by adding another parameter to the function. We have one at the moment, called msgText. Modify your function definition at the top of the code, like this:
def textDraw(msgText, XYPosition):
    font = pygame.font.Font(fontName, 22)
    text_surface = font.render(msgText, True, white)
    screen.blit(text_surface, XYPosition)
  • NOTE: Two lines of code need to be changed; the first and last lines in the function definition. It should look like this:

7-4.png

  • We'll also need to modify the function call so that we send it the values we want to use in our program.
  • Change this line in your game loop (around line 32) to send over more information about where we want the text to appear.
textDraw("Good morning, Dave", (400, 60))
  • It should look like this:

7-5.png

  • Try running the code.
  • If you're unsure of how to complete the tasks so far, this video tutorial explains how to go about them:

Badge It

  • Silver:
    • Add 2 more function calls using your textDraw() function to draw more text at different points on the screen. Add comments to your code, and upload it to BourneToLearn.com
  • Gold:
    • Add another paramenter to your function to control the text size.
    • Draw the words small, medium and lage below each other on the screen, each in different sizes.
    • Upload the code for marking.
  • Platinum:
    • Modify the program so it displays a mouse click counter on the screen, OR
    • Modify your function call so the text moves across the screen.
    • Upload your code for marking.