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Damocles

Rotation, atan2, headaches

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Okay, so I''m using atan2(var,var) to get the angle between two points. No problem there. However, atan2 returns a value between -pi and pi. When converted to degrees it''s between -180 and 180 degrees. The problem is that I have been using the gained angle to slowly rotate an object to face another. I simply use: rotation+=desiredRotation-rotation*(deltaTime*8); desiredRotation being the angle gained from atan2 and the dT*8 being to limit the speed to 8 degrees of rotation per second. The problem arises in that when the angle from atan goes around a full circle, it leaps from 180 to -180 and the object has to do a complete spin in the wrong direction to match up. At first I figured it would be a simple case of using: rotation+=(desiredRotation+360)-(rotation+360)*(deltaTime*8); Alas no. And indeed, alas no to all my other attempts to circumvent this problem. So now I officially hand in the towel and am begging for the solution to what seems like a simple problem. I do hate it when I can''t figure out these simple things.....I wonder if I could sue my high school maths teacher

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well, if you know vectors then, ill tell you how you can find if the current rotation is Clock-wise or counter-clockwise of the objective. I know the problem is 2D but we will pass through 3D space to solve it:

v=(cos(rotation),0,(sin(rotation))
w=(cos(desiredRotation),0,(sin(desiredRotation))... note that cos and sin are passed values in radians.

now let u=v x w (3D crossproduct operator)...

if u.y >0, then v is on one side of w (not sure which) and
if u.y <0, then v is on other side of w

and depending on the side, you either add or subtract angle by a constant amount*dt, until you reach within some tolerence of the objective. (this method ensures constant angular velocity)

you can also stop using atan2 if you wanted to...then w would be the vector between the seeker and the objective.

SporadicFire

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Thanks, the abs(desiredRotation) was the right way to go. Although, I''m not sure if you misunderstood my post or just made a small mistake - but it should have been:

abs(desiredRotation-rotation)>180

At first I was thinking - hmm...that shouldn''t work but maybe he knows something I don''t, and tried it anyway. Then I realised what you meant.

And it''s at times likethese that I wonder if I''m cut out for programming games I really should have been able to see that solution myself

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I realised after I posted that I had made a mistake... figured you''d suss it though.

"Most people think, great God will come from the sky, take away everything, and make everybody feel high" - Bob Marley

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