Learn to Program with Small Basic

Lines 2–8 set up the GraphicsWindow object. Line 10 defines the line feed
character (for appending new lines to the strings). Lines 12–22 define the
rhyme array, which contains the strings for this rhyme. Note how the elements
of this array relate to the boxes in Figure 18-8. Line 24 creates the Next button,
and line 25 registers the handler for the ButtonClicked event. Then the
nextLine variable is set to 11 to point to the 11th element of the rhyme array,
which is the first page of the story (line 26), and OnButtonClicked() is called
to show the first page of the rhyme (line 27).
Now we’ll add the OnButtonClicked() subroutine in Listing 18-12. This
subroutine is called when the user clicks the Next button.
1 Sub OnButtonClicked
2 img = Program.Directory + "\Page" + (12 - nextLine) + ".png"
3 GraphicsWindow.DrawImage(img, 0, 0)
4
5 strOut = "This is "
6 For N = nextLine To 11
7 strOut = Text.Append(strOut, rhyme[N])
8 EndFor
9 GraphicsWindow.DrawText(10, 10, strOut)
10
11 nextLine = nextLine - 1
12 If (nextLine = 0) Then
13 nextLine = 11
14 EndIf
15 EndSub
Listing 18-12: The OnButtonClicked() subroutine
Line 2 fills img with the name of the image for the current page of the
rhyme. When nextLine is 11, we’ll show Page1.png (which is 12 minus 11).
When nextLine is 10, we’ll show Page2.png (12 minus 10), and when nextLine
is 9, we’ll show Page3.png (12 minus 9), and so on. Line 3 draws the image
on the graphics window. We then build up the output string (lines 5–8).
We set strOut to "This is " (line 5) and then start a loop that goes from
nextLine to 11 (lines 6–8). When nextLine is 11, the loop runs one time and
appends rhyme[11] to strOut. When nextLine is 10, the loop runs from 10 to 11
and appends rhyme[10] and then rhyme[11] to strOut. Similarly, when nextLine
is 9, the loop runs from 9 to 11 and appends rhyme[9], rhyme[10], and then
rhyme[11] to strOut.
When the loop ends, strOut contains the entire string for the rhyme at
this stage of the story. We display this string using DrawText() in line 9.
Then we decrease nextLine by 1 to point to the previous element in the
rhyme array (line 11). If nextLine becomes 0 (line 12), the story is done, so we
set it back to 11 to start over (line 13). As a result, when the user clicks the
Next button at the last page of the story, the program goes back to displaying
the first page. We’ve finished the tale before it got stale!
Advanced Text Magic 283