Effect: Particle Systems - JavaFX Special Effects - page 33

var deltaX;//change in x location per step
var deltaY;//change in y location per step
init{
//radius = 5;
fill = Color.RED;
//radom direction in radians
var theta = random.nextFloat()*2.0*Math.PI;
deltaX = Math.cos(theta)*speed;
deltaY = Math.sin(theta)*speed;
}
package function doStep(){
//remove particle if particle has expired
if (--initialSteps == 0){
delete this from (parent as Group).content;
}
//advance particle's location
translateX += deltaX;
translateY += deltaY;
}
}
The Particle class has changed only slightly: the attribute duration is now public and a new
attribute called speed was added. The attribute speed is used in the init method to calculate deltaX and
deltaY . The rest of class is unchanged.
It is worth looking at how deltaX and deltaY are calculated. A random angle is generated that
represents the direction the Particle will travel, and this angle is used to calculate deltaX and deltaY .
The following code shows how this is implemented.
var theta = random.nextFloat()*2.0*Math.PI;
deltaX = Math.cos(theta)*speed;
deltaY = Math.sin(theta)*speed;
The change in X per step ( deltaX ) is simply the cosine of the angle theta multiplied by speed . The
change in Y per step ( deltaY ) is the sine of the angle theta , multiplied by speed . The diagram in Figure 2-4
shows these relationships.