I'm trying to move a cube drawn wit OpenGL in a QGLWidget. Here is part of the code:
void Hologram::paintGL() {
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
drawBox();
}
void Hologram::drawBox() {
for (int i = 0; i < 6; i++) {
glBegin(GL_QUADS);
glNormal3fv(&n[i][0]);
glVertex3fv(&v[faces[i][0]][0]);
glVertex3fv(&v[faces[i][1]][0]);
glVertex3fv(&v[faces[i][2]][0]);
glVertex3fv(&v[faces[i][3]][0]);
glEnd();
}
qDebug() << "drawing box";
}
void Hologram::initializeGL() {
/* Enable a single OpenGL light. */
glLightfv(GL_LIGHT0, GL_DIFFUSE, light_diffuse);
glLightfv(GL_LIGHT0, GL_POSITION, light_position);
glEnable(GL_LIGHT0);
glEnable(GL_LIGHTING);
/* Use depth buffering for hidden surface elimination. */
glEnable(GL_DEPTH_TEST);
/* Setup the view of the cube. */
glMatrixMode(GL_PROJECTION);
gluPerspective( /* field of view in degree */ 40.0,
/* aspect ratio */ 1.0,
/* Z near */ 1.0, /* Z far */ 10.0);
glMatrixMode(GL_MODELVIEW);
// qDebug() << "vx:" << vx << "vy:" << vy << "vz:" << vz;
gluLookAt(0.0, 0.0, 5.0, // eye position
0.0, 0.0, 0.0, // center
0.0, 1.0, 0.); // up vector
// Adjust cube position
glTranslatef(0.0, 0.0, -1.0);
}
void Hologram::animate() {
glTranslatef(0.0, 0.0, -0.1);
updateGL();
}
I've implemented a timer that periodically calls animate() via a signal&slot connection. Shouldn't it add -0.1 to the z-coordinate every time when animate() is executed and therefore move the cube in z-direction? Depending on the value I choose, the cube is either not moving (for values approx. <-0.3) or I cannot see it at all (values approx. >0.4). First I thought it either might move very fast and disappear or it moves very slow and therefore I couldn't see any changes. But playing around with z value always ended up in one of the above mentioned cases... Isn't that strange? What am I doing wrong?
Problem solved: The correct way to do it is
void Hologram::paintGL() {
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glLoadIdentity();
glTranslatef(0.0, 0.0, -dz);
drawBox();
}
The reason why I got the strange behaviour described above is due to the fact that the object was clipped by the near/far planes of the perspective set with gluPerspective()...