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Face an point

Started by X5-Programmer Dec 14, 2006 at 2:35 PM 6 replies 1k views

Original Post

Dec 14, 2006 at 2:35 PM

Hello, I have been trying to get the best way to make a function that rotates my character to face a specific point. I have done something like this:



#define PIOVER180  0.0174532925199432957692369076848861f

float rot;

void Face(float pointX, float pointZ)
{
	float x = pointX - PlayerX;
	float z = pointZ - PlayerZ;
	if (x!=0 && z<0)
	{
		rot=((atanf(x/z))/PIOVER180)-180;
	}
	if (x!=0 && z>0)
	{
		rot=((atanf(x/z))/PIOVER180);
	}
}

glRotatef( rot-90.0f, 0.0f, 1.0f, 0.0f ); -- Draw my character -- If someone have any better way to do this please feel free to post. Thanks.

Zakwayda

Dec 14, 2006 at 3:14 PM

I would suggest looking into the atan2() function as an alternative to atan(); it's more stable, and will simplify the code (you won't have to determine the quadrant manually).

Palidine

Dec 14, 2006 at 3:18 PM

To make it look better in game (your current algorithm appears to "snap" the player to the facing angle) you want to clamp the rotation to no more than some max value. i.e. no more than 5degrees per second or whatever number looks good.

You find the angle between the current facing direction and the desired facing direction. if that is 30degrees clockwise, then you'd only rotate Xdegrees clockwise this frame where X is calculated based on your clamping angle.

For extra credit make that max rotation rate tunable in data somewhere so you don't have to re-compile to tune the visual result. for super-extra credit, make it so that you don't have to restart the game to change the number. =)

-me

X5-Programmer

Dec 14, 2006 at 3:32 PM

jyk:

Yah I will look into that, thanks.

Palidine:

About that you said, if you have time to make some example on how to do it? Thanks.

Palidine

Dec 14, 2006 at 3:40 PM

Quote:
Original post by X5-Programmer
About that you said, if you have time to make some example on how to do it? Thanks.

Sadly, no. What I wrote should be enough of an algorithm for you to code it. Was there a specific bit of what I described that was confusing?

-me

Ozymandias42

Dec 14, 2006 at 4:07 PM

Quote:
Original post by jyk
I would suggest looking into the atan2() function as an alternative to atan(); it's more stable, and will simplify the code (you won't have to determine the quadrant manually).

Thank you for bringing this function to my attention. I've always used atan() myself. Yay new and better information!

X5-Programmer

Dec 14, 2006 at 4:10 PM

Palidine:

Yah I can try to make it, Thanks!

dijster

Dec 20, 2006 at 10:02 AM

Try this
angle = ATan2(y1-y2,x1-x2)-90

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