Jittery Movement and Uncontrollable Rotating

Mads FS · 2013-07-28T08:13:57

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: http://pastebin.com/DdjDaiRp

For Beginners

Started by vipar July 27, 2013 09:06 PM

19 comments, last by vipar 10 years, 8 months ago

vipar

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July 28, 2013 08:13 AM

It won't, but it's just easier working in the correct units for the functions, which in the case of angles is radians, since that makes the maths easier. You aren't gonna measure the speed of your car in furlongs per fortnight are you? As soon as you start doing calculus you should forget about degrees entirely. The only other sensible option is wangs, wide angles, which are like wchars but have 65536 wangs in a full circle instead of 2pi radians, since they play nice with integer overflow on computers ;)

[note: I just made up wangs but I like it as a terminology ;)]

And if you are asked to draw a right angled triangle with an angle of 45 degrees, you measure the angle anticlockwise from the x axis don't you? That's how all the trig functions are defined. I have no idea why computer scientists like measuring their angles clockwise from due North myself, maybe they want to be sailors?

Given that a Vectors Rotation is calculated in Degrees (which is how they are defined in SFML [0, 360]) I have to calculate in degrees

It's not a choice.

CEO of Dynamic Realities

Jittery Movement and Uncontrollable Rotating

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