3d camera locking onto a target/z-targeting

Game Mechanics
#1

So, I’m trying to recreate z-targeting from the zelda games in my own, and to do this I plan on using the lookAt function. Unfortunately, it’s not working out for me, even if it is basic trigonometry.

I read the following articles on it:

http://www.euclideanspace.com/maths/algebra/vectors/lookat/index.htm
http://www.ehow.com/how_5717908_calculate-lookat-function.html

My problem is, even if I have the eye coordinates, and the target coordinates, I don’t know what to do about the current target coordinates. All I have available to use are the Yaw and pitch of my camera, so I don’t know how to take these and make the coordinates I need to get the proper dot product.

And even when I do get the dot product, I don’t know what to do about the arccos. In the second tutorial, the author says he got his angle from the arccos of 10. Of course in Java, the input of arccos can’t be over 1, so how do I get around this?

I’m sorry if these are obvious questions, my geometry teacher was terrible so most of my trig is self taught.

Thank you.

#2

Well, I’m hoping your 3D camera is first-person based, then it will be easier. :smiley:

a 3D camera has pitch and yaw, but it can also be represented with a 3 dimensional vector. So, calculate the vector from your target to you, which is basically target.pos - camera.pos, and then you’d need to normalize it.

That’s basically your directional vector, so now you need to figure out how to calculate the pitch and yaw values of the 3D vector. I’ve shown how to convert pitch and yaw to a 3d vector here: http://www.java-gaming.org/topics/pitch-yaw-to-directional-vector/27819/view.html

But now we need the inverse, which I don’t really have an idea how to do. :frowning: Read up and euler angles, and maybe you’ll find something…

I’ll post if I find anything.

#3

I’m not a 3D guy so I don’t know what functions your lib does, but in XNA I had a 3rd person camera that ‘looked at’ a center point. What I would do is start at the X/Y/Z center of the character and then apply rotation matrix. THEN I’d apply a move translation matrix to ‘pull’ the camera back out (and still be looking at the character in a natural way) which seemed to feel natural while playing around with it. Assuming your library has the function, you could then simply perform a ‘look at’ on the camera to then face the enemy, which I would imagine would give it that zelda-like field.

Here’s what I did using the method above (minus look-at of course):

-4n4Nz1xFKQ

#4

In case anyone’s wondering, we solved this over Skype…


	public void lookAt(float targetX, float targetY, float targetZ){
		float dx = targetX - cameraX;
		float dy = targetY - cameraY;
		float dz = targetZ - cameraZ;
		
		yaw = (float)Math.atan2(dx, -dz);
		pitch = (float)Math.atan2(-dy, Math.sqrt(dx*dx + dz*dz));
	}
#5

Camera’s aren’t worth worrying about any performance issues so this is just informational. Skipping euler angles, you have:

The lookat direction from the camera to target (the dx,dy,dz above). Normalize that. Cross it with your up vector (say y, so little computation) and that give the direction to the ‘side’. Normalize that. Cross side and lookat gives camera’s up (no need to normalize…side and lookat are orthogonal). Shove these three vectors into the matrix (row or columns depending on your convention) and you’re done.

forward = (fx,fy,fz) = (dx,dy,dz)/sqrt(dxdx+dydy+dzdz)
side = (sx,sy,sz) = (-fz, 0, fx)/sqrt(fzfz+fxfx)
up = (ux,uy,uz) = (-fysz, fxsz-fzsx, fy*sx)

Assuming I didn’t screw anything up. :slight_smile:

#6

Muh, matrix math is hard! xD The reason why I computed the angles was because I/we have a camera class that works like a first person camera with a yaw and a pitch. By computing those I can just feed those directly into the camera class and be done with it. Hmhmmm…