# OpenGL problem controlling camera using glulookat()

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hello everyone, i'm kinda new to opengl programming, so forgive me the uncorrect things i'm going to write. i also tried looking around for a solution, but didn't find anything... i'm writing a program, and by now i'm trying to perfect the navigation in the world, using keyboard and mouse input. i'd like to use asdw to move forward/backward and rotate left/right, and doing that with the following code:
void key(unsigned char c, int x, int y)
{
int i;
float new_position[3];
float direction[3],direction_n[3],n;
direction[0]=target[0]-eye[0];
direction[1]=target[1]-eye[1];
direction[2]=target[2]-eye[2];
n=(float)sqrt(direction[0]*direction[0]+direction[1]*direction[1]+direction[2]*direction[2]);
direction_n[0]=direction[0]/n;
direction_n[1]=direction[1]/n;
direction_n[2]=direction[2]/n;

if (c == 27)
exit(0);

/* move forward */
if (c=='w' || c=='s')
{
float sign;
sign=c=='w'?+1.0f:-1.0f;

new_position[0]=eye[0]+sign*2*direction_n[0];
new_position[1]=eye[1]+sign*2*direction_n[1];
new_position[2]=eye[2]+sign*2*direction_n[2];

/* rotate */
if (c=='a' || c=='d')
{
const float angle=(c=='a'?1.0f:-1.0f)*M_PI/180.0f;
/* X e Y esprimono il target in funzione dell'eye */
float X=direction[0]*(float)cos(angle)-direction[1]*(float)sin(angle);
float Y=direction[1]*(float)cos(angle)+direction[0]*(float)sin(angle);
target[0]=eye[0]+X;
target[1]=eye[1]+Y;
printf("x e y: %f, %f\n", X, Y);
last_crossed_wall=0;
}

glutPostRedisplay();
}


... and this works well in what it does. the problem comes with mouse input: the movement of the mouse when it's clicked increments the anglex and y, which will be used to do two glRotatef() in the redraw function [glutDisplayFunc(redraw)]. i control mouse input like this:

void mouse(int button, int state, int x, int y)
{
if (button == GLUT_LEFT_BUTTON)
{
if (state == GLUT_DOWN)
{
moving = 1;
startx = x;
starty = y;
}

if (state == GLUT_UP)
{
moving = 0;
}
}
}

/* ---------------------------------------------------------- */
void motion(int x, int y)
{
if (moving)
{
/* since y goes up... */

angley = angley - (y - starty);

anglex = anglex + (x - startx);

float direction[3],direction_n[3],n;
direction[0]=target[0]-eye[0];
direction[1]=target[1]-eye[1];
direction[2]=target[2]-eye[2];

/* ************ i think this is the part i am messing up *********************** */

//float X=direction[0]*(float)cos(anglex)-direction[1]*(float)sin(anglex);
//float Y=direction[1]*(float)cos(anglex)+direction[0]*(float)sin(anglex);
//float Z=direction[2]*(float)cos(angley)+direction[2]*(float)sin(angley);

//target[0]=eye[0]+X;
//target[1]=eye[1]+Y;
target[2]=eye[2]+Z;

printf("angoli- y:%f, x:%f\n", angley, anglex);

startx = x;
starty = y;
glutPostRedisplay();
}
}


(anglex and angley are global vars init=0) actually i just use two glRotatef() to take the angles and rotate the world
glPushMatrix();

/* devo modificare il target a partire da anglex e angley */

glRotatef(-angley, 1.0, 0.0, 0.0);
glRotatef(anglex, 0.0, 1.0, 0.0);

gluLookAt(
eye[0],eye[1],eye[2],
target[0],target[1],target[2],
0.0, 0.0, 1.0);


(...sorry for the bunch of code but i'm trying to be precise) my problem is this: turn 90° left with keyboard 'a'; turn 90° right with mouse; at this point, walking forward with 'w' moves the camera in the "old" direction (the one reached pressing 'a'), not the new one reached with the mouse. basically, i need to change the target[] from mouse input, but didn't find the operations to do that. (thanks for the patience..) --- [Added source tags. /Yann] [Edited by - Yann L on June 4, 2007 6:08:49 PM]

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noone can help? :(

i just need a way to transform my target point of glulookat() from the mouse input...

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Hi,

I don't have the time to debug your program, but if it can help, I use an another technique.
I rotate the target and up the vector in software and then just use gluLookAt. So that i can always have access to the exact position and orientation of the camera.

This is an example in old engine:
http://texel3d.free.fr/projets/progs/abysse_src.zip
Exe can be found here:
http://texel3d.free.fr/projets/index_en.html

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thanks for the code, i will check that later!

(in what our techniques are different? i move the target around the camera using mouse input and then call gluLookat(camera, target, ... ), isn't the same?)

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>in what our techniques are different?

You use glRotate to rotate your camera.
I don't use glRotate. I use sin and cos to compute the position of the target and up vector. After that, i just have to give Position,Target,Up to gluLookAt.

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that's exactly what i intend to do!
now i am using glRotate, but i'm trying to switch to glulookat() using sin and cos as you do.
i think it will work if i'll study your code!

thanks again

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