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Produce the visual and audible effects of the lightening
The purpose of this method is to produce the visible and audible effects of the lightening other than the lightening bolt itself.
The method creates the flash from thelightening bolt, makes the tree more visible during the flash as shown in Figure 2, and plays a sizzle sound that will be followed by a clap of thunder.
Several steps are involved
The method begins by setting the alpha value on the tree image to 1.0 to cause the tree to become totally opaque.
Then it sets the value of the variable named sizzlePlaying to true to notify all other parts of the program that a sizzle sound isbeing played and a lightening bolt is being drawn.
Then it calls the play method on the sizzle Sound . The play method starts the sizzle sound playing and immediately returns a reference to a SoundChannel object through which the sound will be played.
The reference to the SoundChannel object is saved in the instance variable named channel .
Listing 13 registers an event listener on the SoundChannel object that will be executed when the sizzle sound finishes playing.
Finally, Listing 13 sets the red, green, and blue background color component values to dark yellow. These values along with the true value of sizzlePlaying will be used by the code in Listing 7 to set the background color of the canvas to dark yellow the next time the Timer object fires an event.
The drawLightening method
Listing 14 shows the method named drawLightening that is called by the CLICK event handler on the button in Listing 12 to draw the actual lightening bolt.
private function drawLightening():void {lighteningStartX = Math.floor(Math.random()
* canvasObj.width / 3)+ canvasObj.width / 3;
lighteningStartY =Math.random() * canvasObj.height / 10;
lighteningEndX = canvasObj.width / 2 -6;lighteningEndY =
canvasObj.height - treeBitMap.height + 10;//Draw a zero width dark yellow line to the starting// point of the lightening bolt.
canvasObj.graphics.lineStyle(0, 0x999900);canvasObj.graphics.lineTo(
lighteningStartX, lighteningStartY);//Set the line style to a bright yellow line that is// four pixels thick.
canvasObj.graphics.lineStyle(4, 0xFFFF00);//Declare working variables.var tempX:uint;
var tempY:uint = lighteningStartY;var cnt:uint;//Use a for loop to draw a lightening bolt with
// twenty random segments.for (cnt = 0; cnt<20; cnt++ ) {
//Compute the coordinates of the end of the next// line segment.
tempX = Math.floor(Math.random()* canvasObj.width / 3)
+ canvasObj.width / 3;tempY = tempY + Math.floor(Math.random()
* (lighteningEndY - tempY)/5);//Draw the line segment.
canvasObj.graphics.lineTo(tempX,tempY);}//end for loop//Draw a line segment to the top of the tree.
canvasObj.graphics.lineTo(lighteningEndX, lighteningEndY);//Make the lightening go to ground.
canvasObj.graphics.lineTo(lighteningEndX,
lighteningEndY + treeBitMap.height - 20);}//end drawLightening 
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