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# SFML - Acceleration in Space?

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Guest, the last post of this topic is over 60 days old and at this point you may not reply in this topic. If you wish to continue this conversation start a new topic.

6 replies to this topic

### #1Carlows  Members

Posted 28 June 2013 - 10:36 PM

Yeap, me again, lol. The thing is, I'm trying to give my ship an acceleration as if it were moving in space (zero gravity), if a press the Up arrow key, the ship increases its acceleration, change its direction (to the mouse vector), and so forth. There's the code I already have:

sf::Vector2f Nave::getDirection(sf::Vector2f mousePOS, sf::Vector2f playerPOS, float acceleration, sf::Time& delta)
{
sf::Vector2f direction = mousePOS - playerPOS;

direction = direction / sqrt(direction .x * direction .x + direction .y * direction .y) * aceleration;

return direcion;
}

void Nave::update(sf::Time& delta, sf::Vector2f mousePOS)
{
...

if (sf::Keyboard::isKeyPressed(sf::Keyboard::Up))
{
acceleration += 0.1f;
shipDir = getDirection( mousePOS, shipSprite.getPosition(), aceleration, delta );
}
if (sf::Keyboard::isKeyPressed(sf::Keyboard::Down))
{
acceleration -= 0.1f;
}

if( acceleration > 5.0f )
acceleration = 5.0f;
else if( acceleration < 0.0f )
acceleration = 0.0f;

shipSprite.move( shipDir.x, shipDir.y );
shipSprite.setAngle(angle);

...

}

float Nave::Angle( sf::Vector2f playerPOS, sf::Vector2f mousePOS )
{
float angle = atan2(mousePOS.y - playerPOS.y, mousePOS.x - playerPOS.x );
angle = angle * (180/PI);

if(angle < 0)
{
angle = 360 - (-angle);
}

return angle;
}



Of course there's an obvious problem, first, the deceleration, but most important, when I press the Up arrow again, the new vector direction totally f**ks the last direction, there's a video showing the problem:

Since I didn't find solution just looking at google (my poor English makes it harder, I think there aren't too much good gaming forums on Spanish), I'm looking for some help (duh).

Edit1:

there's a really explicit example of what i'm looking for:

Edited by Carlows, 29 June 2013 - 10:56 AM.

### #2Camilo  Members

Posted 29 June 2013 - 01:28 AM

I would just keep one vector for the speed, then add the normalized mouse direction vector to it:

Vector2f position;
Vector2f speed;

void Nave::update(sf::Time& delta, sf::Vector2f mousePOS)
{
float mouseMagnitude = sqrt(mousePOS.x * mousePOS.x + mousePOS.y * mousePOS.y)
mousePOS = mousePOS / mouseMagnitude;  // probably need to divide this by some constant, too.
speed += mousePOS;
position += speed; // * delta if this is not called at regular intervals
}


### #3stitchs  Members

Posted 29 June 2013 - 03:57 AM

On a side-note; can I ask, where do you declare the variable 'aceleration'? There is also another variable 'acceleration' and these seem to be interchanged within the function, and its first usage. Is this just a typo? Or are you making use of the wrong variable at the wrong time?

### #4Carlows  Members

Posted 29 June 2013 - 07:11 AM

On a side-note; can I ask, where do you declare the variable 'aceleration'? There is also another variable 'acceleration' and these seem to be interchanged within the function, and its first usage. Is this just a typo? Or are you making use of the wrong variable at the wrong time?

Lol, that was my error traducing the code to English

### #5Carlows  Members

Posted 29 June 2013 - 09:44 AM

I would just keep one vector for the speed, then add the normalized mouse direction vector to it:

Vector2f position;
Vector2f speed;

void Nave::update(sf::Time& delta, sf::Vector2f mousePOS)
{
float mouseMagnitude = sqrt(mousePOS.x * mousePOS.x + mousePOS.y * mousePOS.y)
mousePOS = mousePOS / mouseMagnitude;  // probably need to divide this by some constant, too.
speed += mousePOS;
position += speed; // * delta if this is not called at regular intervals
}


I think that doesn't change anything on the behavior...

### #6Camilo  Members

Posted 30 June 2013 - 12:46 AM

I would just keep one vector for the speed, then add the normalized mouse direction vector to it:

Vector2f position;
Vector2f speed;

void Nave::update(sf::Time& delta, sf::Vector2f mousePOS)
{
float mouseMagnitude = sqrt(mousePOS.x * mousePOS.x + mousePOS.y * mousePOS.y)
mousePOS = mousePOS / mouseMagnitude;  // probably need to divide this by some constant, too.
speed += mousePOS;
position += speed; // * delta if this is not called at regular intervals
}


I think that doesn't change anything on the behavior...

I think it does: I am treating the speed as a vector, while your "acceleration" (actually speed, I think) is a scalar.

### #7Carlows  Members

Posted 30 June 2013 - 11:37 AM

I would just keep one vector for the speed, then add the normalized mouse direction vector to it:

Vector2f position;
Vector2f speed;

void Nave::update(sf::Time& delta, sf::Vector2f mousePOS)
{
float mouseMagnitude = sqrt(mousePOS.x * mousePOS.x + mousePOS.y * mousePOS.y)
mousePOS = mousePOS / mouseMagnitude;  // probably need to divide this by some constant, too.
speed += mousePOS;
position += speed; // * delta if this is not called at regular intervals
}


I think that doesn't change anything on the behavior...

I think it does: I am treating the speed as a vector, while your "acceleration" (actually speed, I think) is a scalar.

You were right, my fault. Thanks!

Edited by Carlows, 30 June 2013 - 11:37 AM.

Old topic!

Guest, the last post of this topic is over 60 days old and at this point you may not reply in this topic. If you wish to continue this conversation start a new topic.