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Updating Rotation problem

Started by BlackSeeds Oct 7, 2008 at 2:28 PM 1 replies 550+ views

Original Post

Oct 7, 2008 at 2:28 PM

Hi, I've got an issue in XNA which is driving me insane and I'm confused as to whats going on. Basically I'm new to XNA but experienced in OpenGL and Direct X with c++. I want to tween between rotations for a tank game so when you press the analog stick you new rotation is set to the orientation of the stick, and for smooth movement I want to blend between current rotation and the new rotation. Simple enough, I have already implemented similar things before so just did the code as usual and expected it to work... but no it doesn't. what I get is the sprite randomly spinning around franticly before it stops,


//intialisation
int baseRotation = 0;
int intRot = 45;

        public void move(GameTime gameTime)
        {
            if (baseRotation < intRot)
            {
                int diff = intRot - baseRotation;

                if (diff <= 5)
                {
                    baseRotation = intRot;
                }
                else
                {
                    baseRotation++;
                }
            }
            else
            {
                baseRotation = intRot;
            }
        }

So from the above source, you would expect baseRotation to update to 40 then get set to the same as intRot and then thats it. If I debug and step through, this happens, just if I run the game it doesn't, it just spins around a few times and then eventually stops. I just call the update function move from inside my main update function. Anyone had any experience of this or am I doing something silly along the way? Just a quick note, I'm not updating based on time or using floats because I initially thought that this was causing the issue but evidently not.

sirob

Oct 7, 2008 at 3:34 PM

Rotation is usually expressed in radians, not in degrees. This means that 45 is actually somewhere at around 14 full turns from 0. So if you're trying to go from 0 to 45 your sprite will turn 14 times before stopping. Also, since you're adding 1 each frame, it'll just in steps of around 60 degrees each frame.

Of course, if you're dividing by 180/PI somewhere in your code, that's probably not the problem. If not, either change your logic to use radians or divide by 180/PI.

BlackSeeds

Oct 7, 2008 at 4:59 PM

yeah i convert to radians before rendering, just used degrees so i could use ints to rule out any issues with floats,

however ill double check that the radians calculation is working correctly to rule out this issue.

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