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Point1 sprite

Drawer sprite
(invisible)

Point2 sprite
Tutor sprite

Figure 6-26: User interface for the equation-finder application

The user drags the two sprites representing the end points of the line
onto the Stage, and the application automatically displays the equation of
the resulting line. The application contains four sprites: Point1 and Point2
are used to mark the two end points of the line; Drawer is a hidden sprite
that draws a straight line between the two points; and Tutor is responsible
for computing and displaying the equation of the line.
The scripts for Point1 and Point2 are very similar. They contain some
logic (not shown here) that restricts the sprites’ locations to the intersec-
tion points of the grid. Essentially, when the user drags the Point1 sprite,
it updates the variables that hold its coordinates (named X1 and Y1) and
broadcasts Redraw. Similarly, when the user drags the Point2 sprite, it
updates the variables that hold its coordinates (named X2 and Y2) and
broadcasts the same message. All four variables (X1, X2, Y1, and Y2) can
only take integer values in the range –9 to 9. You can find the details of
these scripts in the file EquationOfALine.sb2. Let’s now take a look at the
scripts for the Drawer sprite, shown in Figure 6-27.

Figure 6-27: Scripts for the Drawer sprite

148 Chapter 6
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