Learning Processing: A Beginner's Guide to Programming Images ...

312 Learning Processing
textAlign(CENTER);
text( " This text is centered. " ,width/2,60);
textAlign (LEFT) ;
text( " This text is left aligned. " ,width/2,100);
textAlign(RIGHT);
text( " This text is right aligned. " ,width/2,140);
}
textWidth( ) —Calculates and returns the width of any character or text string.
Let’s say we want to create a news ticker, where text scrolls across the bottom of the screen from left
to right . When the news headline leaves the window, it reappears on the right-hand side and scrolls
again. If we know the x location of the beginning of the text and we know the width of that text, we can
determine when it is no longer in view (see Figure 17.4). textWidth( ) gives us that width.
To start, we declare headline, font, and x location variables, initializing them in setup( ) .
// A headline
String headline = " New study shows computer programming lowers cholesterol. " ;
PFont f; // Global font variable
float x; // Horizontal location of headline
void setup() {
f = createFont( " Arial " ,16,true); // Loading font
x = width; // Initializing headline off-screen to the right
}
Th e draw( ) function is similar to our bouncing ball example in Chapter 5. First, we display the text at the
appropriate location.
// Display headline at x location
textFont(f,16);
textAlign(LEFT);
text(headline,x,180);
We change x by a speed value (in this case a negative number so that the text moves to the left.)
// Decrement x
x = x – 3;
textAlign() sets the alignment
for displaying text. It takes one
argument: CENTER, LEFT, or RIGHT.
Now comes the more diffi cult part. It was easy to test when a circle reached the left side of the screen. We
would simply ask: is x less than 0? With the text, however, since it is left-aligned, when x equals zero, it
is still viewable on screen. Instead, the text will be invisible when x is less than 0 minus the width of the
text (see Figure 17.4 ). When that is the case, we reset x back to the right-hand side of the window, that
is, width .