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Rickwi22

OpenGL OpenGL Camera system

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I was trying to make a camera system in OpenGL and I heard since there is no camera you just move and rotate everything else. I tried to come up with how to do this last night and I just implemented it this morning so its pretty messy. But here is what I have. float CameraRot[] = {0.0f, 0.0f, 0.0f}; float CameraPos[] = {0.0f, 0.0f, 0.0f}; //arrays for holding cameras position and rotation In my input handling I have this. //this seems to work fine and it makes it seem like the camera is moving right, left, back, and forward if (keyPressed[''W'']) CameraPos[2] = CameraPos[2] + 0.1f; if (keyPressed[''S'']) CameraPos[2] = CameraPos[2] - 0.1f; if (keyPressed[''D'']) CameraPos[0] = CameraPos[0] - 0.1f; if (keyPressed[''A'']) CameraPos[0] = CameraPos[0] + 0.1f; //this stuff is supposed to make it seem like the camera is turning left and right, it seems to work ok when camera is at origin, but afetr i have moved the camer it starts working all screwy if (keyPressed[''Q'']) CameraRot[1] = CameraRot[1] - 0.5f; if (keyPressed[''E'']) CameraRot[1] = CameraRot[1] + 0.5f; In my rendering I have this. glLoadIdentity(); if (CameraRot[0] >= 360.0f) CameraRot[0] = 0.0f; if (CameraRot[1] >= 360.0f) CameraRot[1] = 0.0f; if (CameraRot[2] >= 360.0f) CameraRot[2] = 0.0f; glTranslatef(CameraPos[0], CameraPos[1], CameraPos[2]); glRotatef(CameraRot[0], 1.0f, 0.0f, 0.0f); glRotatef(CameraRot[1], 0.0f, 1.0f, 0.0f); glRotatef(CameraRot[2], 0.0f, 0.0f, 1.0f); //then I Push a matrix and draw everything else, then Pop one at the end. My goal is to have a camera that can move left, right back and forth in relation to where it is facing, and be able to rotate up, down, left, and right. If anyone has made a camera system and would like to share with me how I am going wrong or if I have the wrong idea totally, it would be much appreciated. I am not getting syntax errors or anything like that, its just the camera does not rotate correctly at all.

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youre doing what everybody is starting with and which you will at some point realize cant work for any nontrivial case.

you want to move forward, sideways depending on where youre camera is facing, so obviously you need to either store that information or extract it. hint: store it.

youre rotation is the good old "i''ll just store three angles and.. somehow it doesnt work". angles alone arent enough to store your orientation (at least not without a lot more work thats not worth it).

the minimum you need is two vectors (i.e. viewing direction and "up" or "right"). also the position, so we''re at 3x3 values. add some more, make it 4x4 and you get the good old transformation matrix, storing right, up, forward and position vectors.

nothing special, but hiding all the tedious trigonometry and resulting in the shortest code i could come up with (if you ignore all the culling code etc.):

http://festini.device-zero.de/downloads/camera.zip

its letting opengl do all the math hoping for more optimized versions than what one would hack together with math.h.. the drawback is that writing and reading the modelview matrix might hurt the performance. but since you most likely wont do this more than 1-2 times per frame i wouldnt worry (the same code can be used for objects, though obviously i''d only do this in d3d and/or do some profiling in opengl first)

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this is a very good file you posted there. You mind if I post it up on my site? You can have all the rights and whatever, just trying to put helpful files on my site for programming.

Higher Forces

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Thanks I went over the gametutorials site, and basically copied the CCamera Class code from it to make it sure it worked in my app, and I am basically going over it right now so I can understand exactly how they do it, they seem to use gluLookAt, while I got the impression it was possible with out that.

Trienco I read your post and Im pretty sure I understand what you mean, I just downloaded your code but I havent looked over it, thanks for the help, I was wondering about how to do a camera last night, and this idea popped up in my head, it seemed like it would work, I was very suprised when I got done coding it this morning and the rotations simply would not work ;(

Although I havent looked at your code yet, if I were to use gluLookAt();, then as I remember from Geometry class I would make the Look at parameter 1 unit away from my position parameter and use Cosine and Sine(theta equaling the angle which I wanted to turn) and from all the unit circle stuff I learned the the 2 numbers I got would equal the x and y of the Look At position would it not?

EDIT I got the gametutorials code up and running in my app, but I looked at Triencos code and thanks alot man, I read the readme and although in a few days Im going to right my own camera code Im going to look over yours to see how you organized it and also thanks for the frustum culling bit that should be helpful.

[edited by - rickwi22 on June 17, 2003 3:45:42 PM]

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quote:

this is a very good file you posted there. You mind if I post it up on my site? You can have all the rights and whatever, just trying to put helpful files on my site for programming.


no prob.. if you consider it worth mentioning and/or helpful just go along. and i dont think it is special enough to care about any rights ,-)

quote:

it seemed like it would work, I was very suprised when I got done coding it this morning and the rotations simply would not work ;(



part of it will work. as long as you stick to simple first person style it shouldnt cause any problems.
the problem is, that if you just update angles you loose all information about when which rotation was applied. think about it. if you rotate up, then roll left and then up again then the up rotations are in completely different directions.

glrotate will always rotate in local space which is changed by the rotations. thats why just storing the sum of all rotations won''t work.

for first person you would simply rotate around 0,1,0 first (the global up) and then around 1,0,0 (by now the local right). a simple way but only working because one axis is independent of the other.

quote:

and from all the unit circle stuff I learned the the 2 numbers I got would equal the x and y of the Look At position would it not?



quite right, as long as you stick to 2 dimensions. for up/down you have to go from there. but keep in mind that this way you rotate around global axes.
maybe missing a few cases but i''d say for first person go with two angles and for anything else use a matrix or quaternions.

quote:
Im going to look over yours to see how you organized it and also thanks for the frustum culling bit that should be helpful.



hm.. "organized" doesnt sound like code from me *lol* anyway, you''ll find versions for local and global transformations. one reason is for mentioned first person usage the other that for some things you might want to influence it from "outside" and independent of its current orientation.

culling is a little different from the common approach. for one reason, because its the way that feels more "natural" to me after coming up with it in conjunction with a radar and also because it doesnt require extracting or updating normals and should take a few dot products less.

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I dont know if you have ever looked at the gametutorials code, but it seems to use vector math and stuff like to move the camera, how do I do it "using matrixes and quaternions". Right now I use code based off the gametutorials site, where I move the mouse to look around, press "w" and "s" to go forward and backward, and "a" and "d" to strafe right and left.

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its not much difference.. if you do the vector math yourself you will have to construct a matrix (or use glulookat which is doing the same). if you''re lazy like me then you dont want to worry about keeping it orthonormal and use slow sin/cos functions and just hope that the functions of opengl are more efficient.

when you rotate you most likely recalculate two vectors, when i rotate i tell opengl to apply it to the matrix (which will transform all 3 vectors and hopefully doesnt even think about changing the position vector). depending on how often you rotate the camera in one frame its more or less work. you transform one more vector, but you dont have to do the cross products and normalizations. the code is shorter and "cleaner" but the result and the math going on is quite the same.

the "matrix"-way is what you find in my download for opengl and d3d. quaternions would just be another way to do the rotations.

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Ok, soon I am going to go over and compare both ways just so I am sure I understand it fully, thanks for the explanation.

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