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09.15.2008 at 05:12PM PDT, ID: 23733731
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OpenGL (Timer Function)

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OpenGL Graphics & Game Programming, Microsoft Visual C++

I'm working on an OpenGL program that spins a "square".  

Below is the code thus far.   Instead of the "void spinDisplay" function, I now want to use a "timer" function (included below the spinDisplay).    When simply commenting out the spinDisplay, I get a compile error.    

What am I missing?   Do I need to keep portions of the spinDisplay or is my timer_func incorrect (or placed incorrectly within the program)?

Thanks,
EEH
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#include <stdlib.h>
#include <math.h>
#include <GL/glut.h>
 
#define DEGREES_TO_RADIANS 3.14159/180.0
 
static GLfloat spin = 0.0;
GLfloat x, y;
 
void square()
{
 	glBegin(GL_QUADS);
       	glVertex2f(x, y);
       	glVertex2f(-y, x);
       	glVertex2f(-x, -y);
       	glVertex2f(y,-x);
    glEnd();
}
 
void display()
{
    glClear(GL_COLOR_BUFFER_BIT);
    square();
    glutSwapBuffers ();
}
 
 
void spinDisplay ()          // ORIGINAL FUNCTION
{
    spin = spin + 2.5;
    if (spin > 360.0) spin = spin - 360.0;
    x = 25.0 * cos(DEGREES_TO_RADIANS * spin);
    y = 25.0 * sin(DEGREES_TO_RADIANS * spin);
    glutPostRedisplay();
}
 
 
void timer_func(int n)           // NEW FUNCTION
{
	// Update the object positions, etc.
	glutPostRedisplay();
         //glutTimerFunc(n, timer_func, n); 
	glutTimerFunc(5, timer_func, 5);
}
 
 
void myinit ()
{
    glClearColor(0.0, 0.0, 0.0, 1.0);
    glColor3f(1.0, 0.0, 1.0);
    glShadeModel(GL_FLAT);
}
 
void mouse(int btn, int state, int x, int y)
{
   	if (btn == GLUT_LEFT_BUTTON && state == GLUT_DOWN)
    	glutIdleFunc(spinDisplay);
    if (btn == GLUT_MIDDLE_BUTTON && state==GLUT_DOWN)
    	glutIdleFunc(NULL);
}
	
void myReshape(int w, int h)
{
    glViewport(0, 0, w, h);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    if (w <= h)
    glOrtho (-50.0, 50.0, -50.0*(GLfloat)h/(GLfloat)w,
        50.0*(GLfloat)h/(GLfloat)w, -1.0, 1.0);
    else
    glOrtho (-50.0*(GLfloat)w/(GLfloat)h,
        50.0*(GLfloat)w/(GLfloat)h, -50.0, 50.0, -1.0, 1.0);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity ();
}
 
/*  main loop
 *  open window with initial window size, title bar,
 *  RGBA display mode, and handle input events
 */
int main(int argc, char** argv)
{
 
    glutInit(&argc,argv);
    glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGB);
    glutCreateWindow("double buffered");
    myinit ();
    glutDisplayFunc(display);
    glutReshapeFunc (myReshape);
    glutIdleFunc (spinDisplay);
    glutMouseFunc (mouse);
 
    glutMainLoop();
}
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Answered By: mitsujin
Expert Since: 08/25/2008
Accepted Solutions: 1
Computer Expertise: Intermediate
Education: Edith Cowan University, Bachelor's Degree
mitsujin has been an Expert for 4 months, during which he has posted 11 comments and answered 1 question. mitsujin is just one of 71 experts in the OpenGL Graphics & Game Programming Zone. 1 expert collaborated on this answer, which was graded an "A" by the asker.
 
 
20081119-EE-VQP-48 / EE_QW_2_20070628