Bullet Mechanics « cocos2d for iPhone

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Bullet Mechanics

(5 posts) (4 voices)

Started 2 years ago by Kahless
Latest reply from Kahless

Tags:

Bullet projectile mechanics

Kahless
Member
Hey all,

Trying to get my projectiles to fire on a 180 degree arc every 10 degrees using sin and cos to calculate the necesary coords and taking degrees to radians into account, the bit of code i am using just seems to fire them all in one line at 0 degrees. Just wondering if anyone can see where my code is wrong.
```
for(Enemybullet *eb in ebulletarray){	

		 for( float angle = 0; angle <= 180; angle = angle+10){
			 float x = cos(M_PI/180 * angle)*600;
			 float y = sin(M_PI/180 * angle)*600;
			 id a21 = [MoveBy actionWithDuration:3 position:ccp(x,y)];		

			 if([eb getCanfire]){
					eb.visible = YES;
					eb.position = ccp(160,370);
					[eb setCanfire: NO];
					[eb setDead: NO];
					[eb runAction: [[a21 copy]autorelease]];
				}
	 }
	 }
```
It seems like the x and y are not changing or moveby isnt implementing the changes.

I am trying to make one of those fancy bullet patterns you get in most top down shooters.
Any ideas would be appreciated.
Posted 2 years ago #
Lam
Member

You are running multiple actions for one bullet.

I think you want to run one action for multiple bullets. This means you can remove that angle for loop.

Also you instantiate a move action ever time but then you copy it for the runAction which is an extra instantiation I don't think you'll need

Posted 2 years ago #
chrisco
Member
Hi Kahless,

Something like this might work for you:
```
float angle = 0;
for(Enemybullet *eb in ebulletarray){	

          if([eb getCanfire]){
			 float x = cos(M_PI/180 * angle)*600;
			 float y = sin(M_PI/180 * angle)*600;
			 id a21 = [MoveBy actionWithDuration:3 position:ccp(x,y)];		

			 eb.visible = YES;
			 eb.position = ccp(160,370);
			 [eb setCanfire: NO];
			 [eb setDead: NO];
			 [eb runAction: a21];

			 angle += 10;
			 if (angle > 180) {
			                angle = 0;
                          }
	    }
 }
```
I haven't tested this or anything, but it should be close to what you're looking for. You may as well check early on to see if the bullet can fire - if not, there's no need to do your math or create your action. Lam's right about the copy and autorelease as well - it's not necessary.

The part that I'm not completely sure of is where I've place "angle += 10;" and the if statement directly following it. It's set up so that each bullet that can fire will fire at 10 degrees higher than the previous bullet, and at 180 degrees, this resets to zero. I think this is what you were after.

Hope that works for you...
Posted 2 years ago #
mattiasmak
Member

Are you going to do any collision tests for the bullets? If so I would avoid using actions. I think that you should be selective and use actions where it makes sense.

A better way is to move the position of the bullets by your self in a scheduled timer.

In the example above the speed of the bullet will depend on the distance since the action is always 3 seconds.

Posted 2 years ago #
Kahless
Member
@chrisco
Awsome thanks mate! That worked perfectly, i knew i was doing something foolish that i was overlooking.

@Mattiasmak
Yeah i am using collision detection with actions, so far i do not have any problems with it. Just using a circle to circle collision routine.
```
-(BOOL) shipCircle:(CGPoint) circlePoint shipRadius:(float) radius enemyBulletCircle:(CGPoint) circlePointTwo enemyBulletRadius:(float) radiusTwo
{
	float xdif = circlePoint.x - circlePointTwo.x;
	float ydif = circlePoint.y - circlePointTwo.y;

	float distance = sqrt(xdif*xdif+ydif*ydif);

	if(distance <= radius+radiusTwo) return YES;

	return NO;
}
```
Works fine for me.

And the speed of my bullets is not a problem as they always attempt to travel the same distance 600 pixels, enought to clear corner to corner of the screen which is about 577 i believe. Thanks for your input though, you never know i may have to go down that route and stop using actions for more complex travel paths.
Posted 2 years ago #

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