Freeglut glew glutIdleFunc cause lag

Question

I'm just starting out with freeglut and glew and getting it running was already quite hard for me. So now I started coding with tutorials from swiftless and I had a square displayed worked fine. Now I got to the point where I want to make the square move with the arrow keys.

From the point I inserted the glutIdleFunc it started lagging. I cant move the window or click on anything else for about a minute. If I try draging the window then it moves after about 2 min.

I tried doing this with the following code :

#include <GL/glew.h> 
#include <GL/glut.h>

bool* keyStates = new bool[256]; 
float positionX = 0;
void renderPrimitive (void) 
{
    glBegin(GL_QUADS);
    glVertex3f(-1.0f, -1.0f, 0.0f); // The bottom left corner
    glVertex3f(-1.0f, 1.0f, 0.0f); // The top left corner
    glVertex3f(1.0f, 1.0f, 0.0f); // The top right corner
    glVertex3f(1.0f, -1.0f, 0.0f); // The bottom right corner
    glEnd();
}
void keySpecial (int key, int x, int y) 
{
    if (keyStates[GLUT_KEY_RIGHT]) 
    {   
        positionX++;
    }
}

void display (void) 
{

    glClearColor(1.0f, 0.0f, 0.0f, 1.0f); // Clear the background of our window to red
    glClear(GL_COLOR_BUFFER_BIT); //Clear the colour buffer (more buffers later on)
    glLoadIdentity(); // Load the Identity Matrix to reset our drawing locations
    glTranslatef(0.0f, 0.0f, -5.0f);
    renderPrimitive();
    glFlush(); // Flush the OpenGL buffers to the window
}

void reshape (int width, int height)
{
    glViewport(0, 0, (GLsizei)width, (GLsizei)height); // Set our viewport to the size of our window
    glMatrixMode(GL_PROJECTION); // Switch to the projection matrix so that we can manipulate how our scene is viewed
    glLoadIdentity(); // Reset the projection matrix to the identity matrix so that we don't get any artifacts (cleaning up)
    gluPerspective(60, (GLfloat)width / (GLfloat)height, 1.0, 100.0); // Set the Field of view angle (in degrees), the aspect ratio of our window, and the new and far planes
    glMatrixMode(GL_MODELVIEW); // Switch back to the model view matrix, so that we can start drawing shapes correctly
}

void keyPressed (unsigned char key, int x, int y) 
{
    keyStates[key] = true; // Set the state of the current key to pressed
}

void keyUp (unsigned char key, int x, int y)
{
    keyStates[key] = false; // Set the state of the current key to not pressed
}

int main (int argc, char **argv) 
{
    glutInit(&argc, argv); // Initialize GLUT
    glutInitDisplayMode (GLUT_SINGLE); // Set up a basic display buffer (only single buffered for now)
    glutInitWindowSize (500, 500); // Set the width and height of the window
    glutInitWindowPosition (100, 100); // Set the position of the window
    glutCreateWindow ("Your first OpenGL Window"); // Set the title for the window

    glutDisplayFunc(display); // Tell GLUT to use the method "display" for rendering

    glutReshapeFunc(reshape); // Tell GLUT to use the method "reshape" for reshaping
    glutIdleFunc(display);
    glutKeyboardFunc(keyPressed); // Tell GLUT to use the method "keyPressed" for key presses
    glutKeyboardUpFunc(keyUp); // Tell GLUT to use the method "keyUp" for key up events
    glutSpecialFunc(keySpecial);
    glutMainLoop(); // Enter GLUT's main loop
}

I don't expect this to be a hardware problem since my computer can play big games.

Answer 1

You should avoid doing any GL drawing in the idle function. If you want to redraw your scene continuously, use an idle function like

void idle(void)
{
    glutPostRedisplay();
}

and see if that helps.