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Rotating a sprite to look at mouse problem - SFML


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#1 mypel16000   Members   -  Reputation: 46

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Posted 07 January 2013 - 04:42 PM

I just cannot fix this problem about rotating sprites around the mouse. The formula seems fine to me and it is similar to others I have googled. I just cannot figure out why it is behaveing in such a weird way.

 

void Animation::checkRotation(int x, int y, sf::Sprite& backSprite, int px, int py)
{
    yOffset = y - py;
    xOffset = x - px;
    backSprite.SetCenter(px +200, py + 400);
    a = (atan2(yOffset, xOffset)) * 180 / 3.141592;
    backSprite.SetRotation( a );
}

 

where x and y are the mouse coordinates and px and py the sprite image coordinates. I thought that maybe when the sprite rotates, the x and the y also change dynamically, in that case, would there be a solution?

 

I just need a way to get my image looking at the mouse cursor. The sprite.getCenter() doesn't work so I cannot get the center of the image coordinates. Any ideas?

 

P.S: I am using SFML 1.6

 



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#2 BeerNutts   Crossbones+   -  Reputation: 2998

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Posted 07 January 2013 - 04:59 PM

You should not be calling SetCenter.  SetCenter sets the center point of the object, and it's relative to the object; so, typically the "center" is the upper left of the sprite (0, 0), but you could set it to (ImageWidth/2,ImageHeight/2) and the "Center" would be the center of the image.  This would then be where the "position" of the sprite used.

 

So, don't use SetCenter here; it should be used (if at all) only once when the sprite is created, unless you're doing some really specilized stuff.  Just use setPosition() and getPosition() and assume the sprite uses upper left for it's position and you'll be good.

 

Otherwise, the code looks OK.  the x and y position of the sprite should not change at all.  BTW, the sfml-dev.org forums are very good, you can always ask the SFML specific questions there too.

 

Good luck.


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#3 ultramailman   Prime Members   -  Reputation: 1585

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Posted 08 January 2013 - 01:46 AM

I've never used sfml before, but some quick googling tells me that getCenter and setCenter is not related to the sprite's position. What it actually does is setting the center for transformations.
source: http://en.sfml-dev.org/forums/index.php?topic=1968.msg12860#msg12860

#4 minibutmany   Members   -  Reputation: 1674

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Posted 08 January 2013 - 11:03 AM

Instead of using atan2, use a regular arc tangent and give the slope.


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#5 Khatharr   Crossbones+   -  Reputation: 3036

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Posted 09 January 2013 - 10:34 PM

Instead of using atan2, use a regular arc tangent and give the slope.

Why?


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