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# Character Rotation to direction of movement

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Guest, the last post of this topic is over 60 days old and at this point you may not reply in this topic. If you wish to continue this conversation start a new topic.

6 replies to this topic

### #1MrChrisnis  Members

Posted 18 April 2013 - 11:33 AM

Hi,

I have got my character to rotate so that it faces the direction that it will be moving when the W key is pressed, however this only works for a certain amount to each side. I cannot turn my camera 180 degrees and have the character follow it. The code I am using is shown below.

void Game::calcRotAngle(Model *p) {
float dot = xAxis.DotProduct(heading);

float theta = acos(dot);

float angle = theta * 180/PI;

p->rotAngleZ = -angle;

/*char text[256];
sprintf_s(text, "Angle: %5f", angle);
DebugOut(text);*/
}


The "heading" Vector is calculated from the position the camera is looking at - the camera's eye position to get the forward vector for where the camera is looking.

Can anybody help me to understand why this isn't working as I want it to?

Thanks,

Chris

### #2Paradigm Shifter  Members

Posted 18 April 2013 - 11:47 AM

acos only returns angles in a 180degree (pi radians) range.

Use atan2(y, x) instead, that returns a full 360 degree range.

EDIT: Better still drop the trig and use your facing (normalise it and scale by movement speed) for your velocity.

Edited by Paradigm Shifter, 18 April 2013 - 11:48 AM.

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

### #3MrChrisnis  Members

Posted 18 April 2013 - 02:27 PM

Hi,

Thanks for your reply so fast.

I have the stuff you mentioned in your Edit for my velocity setting. The problem was just getting the character to rotate to face the way it is moving.

In regards to the atan2, what would I actually be using for the parameters of that function?

Sorry, I've just been trying to get this rotation working for quite a while now and staring at it makes me annoyed now

Thanks,

Chris

### #4Paradigm Shifter  Members

Posted 18 April 2013 - 02:34 PM

The arguments for atan2 are the y and x coordinates of the triangle, angle = atan2(y, x). y = opposite, x = adjacent in trig-speak, remember that tan(theta) = opposite/adjacent.

EDIT: 0 radians is facing due east, pi/2 is north, pi (or -pi) is west and -pi/2 is south.

Edited by Paradigm Shifter, 18 April 2013 - 02:37 PM.

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

### #5MrChrisnis  Members

Posted 18 April 2013 - 02:35 PM

Oh wow, I totally should have known that...

Thanks again for the help. I feel really stupid right now

### #6Paradigm Shifter  Members

Posted 18 April 2013 - 03:04 PM

atan2 doesn't do anything magic by the way, it just calls atan(y/x) and then it adjusts the sign of the angle based on the signs of y and x (and also does the correct thing if x = 0 [i.e. it returns pi/2 if y is positive and -pi/2 if y is negative. If y is zero as well as x, the return value wont make any sense]). That's how it can return an angle in the full -pi to pi range, it works out which quadrant the angle is in.

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

### #7MrChrisnis  Members

Posted 18 April 2013 - 04:11 PM

Ahhh, thank you for the extra explanation. Now I just need to try to remember that for the future

The code is now working properly and my character rotates as expected.

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