Opengl glRotatef rotating a polygon, won't rotate in place - opengl

Question

I'm trying to rotate a polygon in place, but it keeps revolving instead.
To rotate, I calculate the center by finding the average location of each vertex. I call the rotation functions and then call a translation using the center to move it to the middle of the screen. It does end up centered, but it still rotates as if it's not. Any ideas as to what I could be doing wrong?
Here's my code:
void Polygon::DrawPolygon()
{
glPushMatrix();
glLoadMatrixf(matrix);
glTranslatef(displace[0], displace[1], displace[2]);
glRotatef(rotation[0], 1, 0, 0);
glRotatef(rotation[1], 0, 1, 0);
glRotatef(rotation[2], 0, 0, 1);
glTranslatef(-displace[0], -displace[1], displace[2]);
displace[0] = 0; displace[1] = 0; displace[2] = 0;
glGetFloatv(GL_MODELVIEW_MATRIX, matrix);
DrawMaterial();
DrawFaces();
ConnectFaces();
glPopMatrix();
}
Here's how I calculate the center:
void Polygon::FindCenter()
{
float x = 0;
float y = 0;
float z = 0;
for(int j = 0; j < 2; j++)
{
for(int i = 0; i < vertexCount; i++)
{
x += vertices[i][0];
y += vertices[i][1];
z += vertices[i][2] + extrusionDistance * j;
}
}
x = x / (vertexCount * 2);
y = y / (vertexCount * 2);
z = z / (vertexCount * 2);
displace[0] = x;
displace[1] = y;
displace[2] = z;
}
Because of the way my extrusion works I don't need to add the x and y for the vertices of both faces, but I did anyway to keep it consistent.
Here is how I draw the shape:
void Polygon::DrawFaces()
{
for(int j = 0; j < 2; j++)
{
glBegin(GL_POLYGON);
for(int i = 0; i < vertexCount; i++)
{
glVertex3f(vertices[i][0], vertices[i][1], j*extrusionDistance);
}
glEnd();
}
}
void Polygon::ConnectFaces()
{
for(int i = 0; i < vertexCount; i++)
{
glBegin(GL_POLYGON);
glVertex3f(vertices[i][0], vertices[i][1], 0);
glVertex3f(vertices[i][0], vertices[i][1], extrusionDistance);
glVertex3f(vertices[(i+1)%vertexCount][0], vertices[(i+1)%vertexCount][1], extrusionDistance);
glVertex3f(vertices[(i+1)%vertexCount][0], vertices[(i+1)%vertexCount][1], 0);
glEnd();
}
}

Answer 1

I see a few things that stand out to me as being odd:
1) You're calling glLoadMatrixf(matrix) before the call to glTranslate() and glRotate(). Depending on what's in the matrix you're loading, that changes things.
2) You're FindCenter() method calculates the center by including the vertex[i][2] in the calculation of z, but when you actually draw the faces in DrawFaces(), you don't include the vertex[i][2] part, just the extrusion * j part. So you're not drawing the same thing that you're calculating the center of.