glPushMatrix() and glutSolidSphere() do not work together. Why? - opengl

Question

When I write the following code, everything works and an ellipsoid is displayed.
void HandModelCreator::drawModel(){
palm();
}
void HandModelCreator::palm(){
glColor4f(0.6, 0.0, 0.0, 0.0);
glScalef(1.0, 0.3, 0.45);
glutSolidSphere (0.4, 20, 20);
}
I am trying to create a hierarchical model & need to use glPushMatrix() and glPopMatrix(). So, I tried the following code, but nothing really worked. No ellipsoid was displayed. Why? What am I doing wrong?
void HandModelCreator::drawModel(){
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glPushMatrix();
palm();
glPopMatrix();
}
void HandModelCreator::palm(){
glColor4f(0.6, 0.0, 0.0, 0.0);
glScalef(1.0, 0.3, 0.45);
glutSolidSphere (0.4, 20, 20);
}

Answer 1

Why are you calling glLoadIdentity() before pushing the matrix on the stack? The idea of a stack is, that you push before you make the changes you later want to revert.
Furthermore, I don't think you want glLoadIdentity() there at all, because that resets the whole modelview matrix (i.e. whatever transformation hierachy you had, is then gone):
This is closer to what you actually need:
void HandModelCreator::drawModel(){
glMatrixMode(GL_MODELVIEW);
glPushMatrix();
palm();
glPopMatrix();
}

Answer 2

Before pushing the matrix, you set it to identity (using glLoadIdentity). This will of course cancel all previous transformations accumulated into the modelview matrix and might very well be the reason why you cannot see anything.
I advise you to delve a little deeper into how OpenGL's transformation pipeline and matrix transformations in general work.