Object velocity according to touch point.

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Object velocity according to touch point.

(12 posts) (4 voices)

Started 2 years ago by natanavra
Latest reply from symadept

Tags:

CCMoveTo

natanavra
Member
Hi there,
I've been trying to move a sprite with velocity defined by a touch point, I have managed to do this using this:
(btw I'm in portrait mode)
```
UITouch *touch = [touches anyobject];
CGPoint loc = [touch locationInView:[touch view]];
loc = [[Director sharedDirector] convertCoordinate:loc];
CGPoint velocity = ccp(loc.x - object.position.x, loc.y - object.poistion.y);
```
Now this basically works, but the object's speed changes according to the touch point, and I'm looking for a constant speed.
I think this can be achieved using angles but I just can't get it. I can find the angle but I don't know how to direct the object (through velocity) to the point touched, it just goes random.
```
UITouch *touch = [touches anyobject];
CGPoint loc = [touch locationInView:[touch view]];
loc = [[Director sharedDirector] convertCoordinate:loc];
double degrees = (atan2(loc.x - object.position.x, loc.y - object.position.y) *180) / 3.14159265;
CGPoint velocity = ccp(kSpeed * cos(degrees), kSpeed * sin(degrees);
```
I tried this one, but the sprite goes random wherever it wants...
Can anyone explain how to do this and elaborate about the convertCoordinate method as it is very confusing.
Thank you in advance!
Posted 2 years ago #
patrickC
Member
Hum, not too sure here, are you using chipmunk?
If so, are you manually setting v?
At any rate, I would go with the first thing you tried.
You're calculating the vector between the object and the touch position, if you want to move it by a constant amount you could normalize and scale by a constant.
with chipmunk functions:
```
cpVect resultVector = cpvmult(cpvnormalize(velocity),kMoveValue));
```
Hope that's somewhat helpful.
Posted 2 years ago #
Codemattic
Moderator
Maybe:

...
```
CGPoint velocity = ccp(loc.x - object.position.x, loc.y - object.poistion.y);
CGPoint direction = ccpNormalize(velocity);
```
direction is now a unit vector pointing in the same direction as velocity. If you have a speed you want it at then:

CGPoint newVelocity = ccpMult(direction, speed);

[edit] oops, mostly what patrickC said
Posted 2 years ago #
natanavra
Member

Hmmm... Thank you both!
This method works perfectly!!
I didn't really know about the normalize method, so thank you for teaching me something new!

Posted 2 years ago #
symadept
Member

Hi @Natanavra,

I am not able to move my bullet with this following code. Please help me how can I move the bullet.
CGPoint velocity = ccp(_bulletBody->p.x-position.x, _bulletBody->p.y-position.y); CGPoint direction = ccpNormalize(velocity); CGFloat speedMultiplier = 1.0f; CGPoint newVelocity = ccpMult(direction, speedMultiplier);

//This is one way to fire your bullet using chipmunk cpBodyApplyImpulse(_bulletBody, newVelocity, cpvzero);

Regards
Mustafa

Posted 2 years ago #
natanavra
Member

I sure the problem is in this code? it is possible that you are not updating your graphics according to the chipmunks body.
so in the updateShape method did you define:

[(Sprite *)shape->data setPosition:ccp( shape->body->p.x, shape->body->p.y)];

Cause maybe the code of the ApplyImpulse works, but you just can't see it due to graphics not being updated...
I'm not too familiar with chipmunk but the code you posted seems correct...

CGPoint velocity = ccp(_bulletBody->p.x-position.x, _bulletBody->p.y-position.y);

position is the CGPoint of the UITouch?

Posted 2 years ago #
symadept
Member

Hi @Natanavra,

Thank you very much. This works. The actual problem was with the speed factor. It is trying to move but very slowly. After changing speedMultiplier to 20,000, it works with some issues.

Issues
1. In my bulletCollision callback method, I am trying to set the position of the bullet out of the screen such that it should disappear. Again I am doing the same mistake like setting its position = cpv(-50, -50) and velocity = cpvZero.

Do you know any proper way to handle this kind of situation where I can make this bullet to go out of the screen?

2. Sometimes after the bullet hitting the enemy, it abruptly falls down as if it is falling down to the ground.

3. How can I make the bullet disappear if it misses the enemy and but going beyond the Shooter's range.

Kindly help me to resolve these issues.

Thanks in advance.

Regards
Mustafa

Posted 2 years ago #
symadept
Member

One more thing I made a change to that, my direction is exactly opposite so I reversed the direction coordinates to get this done.

1. One more issue I found sometimes the bullet goes in very random direction after hitting the enemy.

Posted 2 years ago #
natanavra
Member
Hmm that's probably chipmunks physics, bouncing your bullet off the enemy.
You already have the bullets vetor, meaning if you keep adding the vector to the current poisiton of the bullet it will eventually go out of the screen;
```
if(bullet->body->p.x > 320.0){
[self removeChild:bullet->data];
cpSpaceRemoveShape(space, bullet);
}
if(bullet->body->p.x < 0){
[self removeChild:bullet->data];
cpSpaceRemoveShape(space, bullet);
}

etc....
```
I think this should work to see if the bullet is out of the screen... notice that x would be > 480 if in landscape (don't forget coordinates). About the bullet hitting the enemy - do you want the bullet going through the enemy? disappearing? lose velocity? bounce?

Can someone help us here? I'm not all too good with chipmunk... I barely know the engine...
Posted 2 years ago #
symadept
Member

cpSpaceRemoveShape(space, bullet); is throwing exception during the step of GameLayer.

And one more thing I could see, for the same behavior, the bullet is shot in some different direction, exactly mirrored angle laterally. But the values that calculated was same in both the cases. It is so much reproduceble that every alternate bullet is hitting like this.

Kindly anybody help me in this.

Regards
Mustafa

Posted 2 years ago #
natanavra
Member

Can you post the exception from the console?
I think it's because removing during a step, so you need to store the value you need to delete and delete after the step, in a different function...
The exception is probably saying that something cannot be mutated while being updated or something like that...

Posted 2 years ago #
symadept
Member

Hi,
I have tested again. There is no such issue of the exception. But the problem still exists even after removing the body & shape. I could see as if it is pushed out from the shooter location. But when I debug the log shows for the same values of the bullet starting and target location and all, this is quite often happening... Every alternate bullet is pushed out.

I really don't know to fix this. Kindly help me in this regards.

Posted 2 years ago #

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