Open GL rotating problem

[nsr]

Hello

I am doing something in Open GL and here is my problem:

I've got polygon rotating around z-axis and I want it to stop rotating at 60 degrees and then return it back to stating point.
How could i do this:
here is the code:

float angle= 1.0;

.......

glPushMatrix();
glTranslatef(-50,0.0,0.0);
glRotatef(-angle,0.0,0.0,0.1);

glBegin(GL_QUADS);

glColor3f(0,0,0); glVertex3f(0.0f, 10.0f, -10.0f);
glColor3f(0,0,0); glVertex3f(0.0f, 10.0f, 10.0f);
glColor3f(0,0,0); glVertex3f( 50.0f, 10.0f, 10.0f);
glColor3f(0,0,0); glVertex3f( 50.0f, 10.0f, -10.0f); glEnd();

glPopMatrix();

[HairyDave]

Don't you just need to alter the angle variable?

I mean, each time you Rotate the matrix, alter the variable to increase the angle of rotation for next time. Before you actually do it, test what the angle is - if its too big, change the value.

HD

[nsr]

OK, but what shell I put in the code, another angle variable or?..
to rotate it back?

[HairyDave]

Well what do you want?

For example, if you want the polygon to rotate to 60 degrees then rotate to -60 degrees etc - like its wobbling, then you can:

#define MAXANGLE 8 // Some max angle
#define MINANGLE -8 // Some min angle

float angle= 0.0; 
int direction = 1;  // Direction of rotation
int increment = 0.1; // Set to some value of increment

....... 

glPushMatrix(); 
glTranslatef(-50,0.0,0.0); 

if(angle > MAXANGLE)
  direction = -1;  // Set to reverse direction
else if(angle < MINANGLE)
  direction = 1;

angle += (direction*increment);
  
glRotatef(-angle,0.0,0.0,0.1); 

glBegin(GL_QUADS); 
glColor3f(0,0,0); glVertex3f(0.0f, 10.0f, -10.0f); 
glColor3f(0,0,0); glVertex3f(0.0f, 10.0f, 10.0f); 
glColor3f(0,0,0); glVertex3f( 50.0f, 10.0f, 10.0f); 
glColor3f(0,0,0); glVertex3f( 50.0f, 10.0f, -10.0f); 
glEnd(); 

glPopMatrix();

Thats probably about right - the values are probably screwed up - its been quite a while since I did OpenGL.

HD

[nsr]

Thanks, this works perfectly...
the only thing is how to set the time so the rotation will occure back after for example 15 seconds...

[HairyDave]

You'll just have to test it. As I say, I haven't done OpenGL for a couple of years - and no graphics programming since - so I'm a bit rusty.

Trial and error, thats the key. Unless you have information on frame rates etc. in which case you 'could' work it out

HD

[nsr]

What do you mean trial and error... is it trial the time sequence which have to be defined and used to set when rotation will go back to....
NSR