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Jittery Movement and Uncontrollable Rotating

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So I've been looking around to try and figure out how I make my sprite face my mouse. So far the sprite moves to where my mouse is by some vector math.
 
Now I'd like it to rotate and face the mouse as it moves. From what I've found this calculation seems to be what keeps reappearing:
 
    Sprite Rotation = Atan2(Direction Vectors Y Position, Direction Vectors X Position)
 
I express it like so:
 
    sp.Rotation = (float)Math.Atan2(directionV.Y, directionV.X);
 
If I just go with the above, the sprite seems to jitter left and right ever so slightly but never rotate out of that position. Seeing as `Atan2` returns the rotation in radians I found another piece of calculation to add to the above which turns it into degrees:
 
    sp.Rotation = (float)Math.Atan2(directionV.Y, directionV.X) * 180 / PI;
 
Now I've added + 90 to the above calculation so that it reads:
 
sp.Rotation = (float)Math.Atan2(directionV.Y, directionV.X) * 180 / PI + 90;
 
It will now face the mouse correctly every time. (This is different since the video was made)
 
Now the sprite rotates. Problem is that it spins uncontrollably the closer it comes to the mouse. One of the problems with the above calculation is that it assumes that **+y** goes up rather than down on the screen. As I recorded in these two videos, the first part is the slightly jittery movement (A lot more visible when not recording) and then with the added rotation:
 
 
So my questions are:
 
 1. How do I fix that weird Jittery movement when the sprite stands
    still? Some have suggested to make some kind of "snap" where I set
    the position of the sprite directly to the mouse position when it's
    really close. But no matter what I do the snapping is noticeable.
 2. How do I make the sprite stop spinning uncontrollably?
 
The code is as follows:
 

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Think about it. When the mouse point is equal to the rotation point, exactly what orientation should the sprite have? A better way to look at it is this: Imagine a point in the exact center of your body. Now, orient yourself to face that point. The results from atan2 at this point are undefined. Edited by MarkS

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Dunno what Atan2 returns for 0, 0 in Java (EDIT: C# even ;)). In C/C++ it returns 0 and sets errno I think. You have to set it to some value, usually the last valid rotation is the best. Better still is to restrict the cursor so it can't get too close to the rotation centre.

Edited by Paradigm Shifter

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I've tried to stop the sprite when it was very close to the cursor to make it stop rotating like that. I know what is causing it. I just don't know how to really fix it.

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Keep track of the mouse position. If the new mouse position is viable, save it and use it to determine the rotation. If it is not viable, discard it and use the stored position to determine rotation. Edited by MarkS

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Keep track of the mouse position. If the new mouse position is viable, save it and use it to determine the rotation. If it is not viable, discard it and use the stored position to determine rotation.

 

I don't think you read the post or the code :/

I am already doing that.

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Keep track of the mouse position. If the new mouse position is viable, save it and use it to determine the rotation. If it is not viable, discard it and use the stored position to determine rotation.

 
I don't think you read the post or the code :/
I am already doing that.


No, you are tracking the rotation. Track the mouse position.

if fabs(old_pos - mouse_pos) > epsilon then
old_pos = mouse_pos
directionV = Normalize(mouse_pos- sp.Position);
else
directionV = Normalize(old_pos- sp.Position);
endif

newRot = (float)Math.Atan2(directionV.Y, directionV.X) * 180 / (float)Math.PI + 90;
Edited by MarkS

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Keep track of the mouse position. If the new mouse position is viable, save it and use it to determine the rotation. If it is not viable, discard it and use the stored position to determine rotation.

 
I don't think you read the post or the code :/
I am already doing that.

 


No, you are tracking the rotation. Track the mouse position.

if fabs(old_pos - mouse_pos) > epsilon then
old_pos = mouse_pos
directionV = Normalize(mouse_pos- sp.Position);
else
directionV = Normalize(old_pos- sp.Position);
endif

newRot = (float)Math.Atan2(directionV.Y, directionV.X) * 180 / (float)Math.PI + 90;

 

Can't really see how I should translate this into C# given a mouse position is given by a Vector2i and a position is given by a Vector2f and by subtracting them you can't get a single number you can compare to Epsilon. Epsilon would have to be either  vector itself to test for "is greater than" or the subtractions of the vectors have to be made into a number.

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That is just pseudo-code. Find the distance between the two points and compare the distance to epsilon.
 
distance = sqrt(((old_pos.x - mouse_pos.x) * (old_pos.x - mouse_pos.x)) + ((old_pos.y - mouse_pos.y) * (old_pos.y - mouse_pos.y)));
if fabs(distance) > epsilon then
...
Edited by MarkS

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Yeah, you meant "length" or "magnitude" rather than fabs.

 

And you want to use the square of the distance in your new example (rather than call sqrt, for efficiency reasons) and compare it to epsilon * epsilon, since if a >= 0 and b >= 0 then a >= b if and only if a2 >= b2

Edited by Paradigm Shifter

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