Learn to Program with Small Basic

to become a value other than 0 (this is called polling; it’s similar to asking
“Are we there yet?” during a long trip). When choice1 becomes a value other
than 0 (line 13), the body of the If block is executed (lines 14–19). We draw
image W3 to show a blank result (lines 14–15). Next, we set the computer’s
choice, choice2, to a random value between 1 and 3 (line 16). Then we call
SwitchImages() to show the images that correspond to choice1 and choice2
(line 17). Then we call ShowWinner() to show the result of this round of the
game (line 18). Finally, we set choice1 back to 0 to tell the OnMouseDown()
subroutine that the main loop is ready for another round of the game
(line 19).
Next, you’ll add each subroutine one at a time.
Step 2: Add the MouseDown Handler
Now let’s handle the MouseDown event to figure out the player’s choice. Add
the OnMouseDown() subroutine in Listing 14-5 to the bottom of the program.
1 Sub OnMouseDown
2 If (choice1 = 0) Then ' Ready for another round
3 y = GraphicsWindow.MouseY ' Vertical click position
4 If ((y > 80) And (y < 120)) Then ' Within range
5 x = GraphicsWindow.MouseX ' Horizontal click
6 If ((x > 40) And (x < 80)) Then ' Rock
7 choice1 = 1
8 ElseIf ((x > 110) And (x < 150)) Then ' Paper
9 choice1 = 2
10 ElseIf ((x > 175) And (x < 215)) Then ' Scissors
11 choice1 = 3
12 EndIf
13 EndIf
14 EndIf
15 EndSub
Listing 14-5: Checking the choice the user clicked
Small Basic calls this subroutine when the player clicks anywhere in the
graphics window. First, the subroutine checks the value of choice1 (line 2).
If choice1 is 0, the subroutine checks where the player clicked to see whether
they clicked one of the three buttons. If choice1 is not 0, that means the
main loop is still processing the player’s last choice, so the subroutine just
ignores the mouse click. This way your game won’t get confused if the
player clicks all over the place.
To see whether the player clicks one of the three image buttons, the
subroutine checks the vertical position of the click (line 4). If it’s within the
range of the images, the subroutine checks the horizontal position (line 6).
The If/ElseIf ladder then compares the horizontal position with the left and
right edges of each image and sets choice1 accordingly (lines 6–12).
202 Chapter 14