In the last tutorial I showed you how to make a turret fire a bullet that doesn’t move. This is little help when creating a turret game, but it leads us on to the next part.

If you think about what exactly we want the bullet to do it is quite simple. All we want it to do is move in a constant speed in the direction that the mouse is pointing. If you look back at the previous tutorial at the createBullet function you can see that the x coordinate is controlled by cos and the y by sin. 

createBullet(turret.x+(40*Math.cos((turret.rotation+90)*degreesToRadians)),turret.y+(40*Math.sin((turret.rotation+90)*degreesToRadians)));

We are going to use the same concepts when making the bullet move.

Can you remember how we used 40*Math.cos to make the bullet appear at the end of the turret, well we are going to increase the x coordinate of the bullet by that, whilst replacing the 40 with the speed of the bullet.

To do this we need to make a function that is triggered every frame that increases the bullets position when triggered. We are going to put this new code into the create bullet function.

var bulletGo = bulletHolder.addChild(bullet);

bulletGo.currentTurretRotation = turret.rotation+90;

bullet.addEventListener(Event.ENTER_FRAME, moveBullet);

function moveBullet(event:Event):void {

bulletGo.x+=Math.cos((bulletGo.currentTurretRotation)*degreesToRadians);

bulletGo.y+=Math.sin((bulletGo.currentTurretRotation)*degreesToRadians);

}

line 1: Creating a variable to handle adding the child of the bullet to the stage. This is to make the variables associated with it independent each time the variables are set. This stops the bullet from changing direction due to the turrets rotation.

line 2: Setting the current rotation variable to the turrets rotation.

line 3: Adding the Enter frame listener to move the bullet.

line 4: Setting up the moveBullet function that is triggered by the event listener in the line above.

line 5: Using the bullet child handler that i set up earlier to move the bullets x coordinate by Math.cos( the rotation of the turret, set by the currentRotation variable in line 2, in radians. As i said before i move the bullet though this handler so that each bullet moves independently of each other.

line 6: Just like above i move the bullets y coordinate by the same method, but use Math.sin.

Full code

changes to previous code:

line 4: I am creating a variable called currentTurretRotation, which you know is where i hold the rotation of the turret when the mouse is clicked.

Example.

In the next tutorial i will show you how to delete the bullets when they go offstage, and maybe add some things to shoot.

This is one of the first things that i tried to do in flash when i first got mx. now i will explain how to rotate a movieClip to face the mouse in adobe cs3.

To start off you can either draw the object that you want to rotate on the stage, or make it entirely in actionscript, as long as its a movieclip with an instance of it on the stage it will work.

First i have to create the object i am going to rotate. i am going to do it in actionscript with the built in drawing API.

I will explain the drawing API in greater detail in a later tutorial. But this code will make a turret shaped movieclip.

turret.graphics.beginFill(0xFFFFFF);
turret.graphics.lineStyle(2, 0xFFFFFF);
var turret:MovieClip = new MovieClip();
turret.graphics.drawRect(-10, 0, 20, 40);
turret.graphics.endFill();
turret.graphics.beginFill(0xFFFFFF);
turret.graphics.drawCircle(0,0,20);
turret.graphics.endFill();
turret.x = 275;
turret.y = 200;
addChild(turret);

 
Ok now to explain the code;

line 1: This introduces a new variable called “turret” which is a movieClip. We can now use the instance “turret” to give it commands.

line2: Using the movieClip.graphics method i am telling the turret movieclip to start a fill colour which is white. the “0xFFFFFF” is a colour hex code. 6 Fs means white.

line 3: This is setting the linestyle of the movieClip to 2 pixels thick and then its colour, again white.

Line 4: This line draws a rectangle in the movieClip instance, the first number is the x coordinate, the second is the y coordinate, the third number is the width and the last number is the height. If you want the object to have dynamic actions applied to it it is best to set the x and y coordinates to 0.

line 5: Telling the movieClip to stop filling in with the colour.

line 6: Setting a new fill, with the same colour as before. If i hadn’t ended the previous fill then part of the movieClip would be transparent.

line 7: This command “drawCircle” does exactly what it says, it draws circles. the numbers are x then y coordinates and then the radius of the circle. The coordinates are set to 0 because we want the turret to rotate about its centre.

line 8: Ending the circle fill colour.

line 9-10:These are setting the x and y coordinates of the turret, these can be anything but i’ve set them to the centre of the stage.

line 11: This is probably the most important line. It adds the movieClip instace to the stage so that we can see it!

Copy these actions in your actions panel and set the background colour to something other than white. I have used black. It should look exactly like this.

In the next part of the tutorial we will make it actually rotate.

Welcome back, At the end of the last tutorial i wondered what would happen if we had a platform that you could jump underneath from.