Question

I am trying to rotate an object around it’s center with the following code :

-(void)render
{
// clear the matrix
glPushMatrix();
glLoadIdentity();

// move to my position

//scale
glScalef(0.000015, 0.000015, 0.000015);

xRotation =280.0;
zRotation =1.0;
yRotation +=0.5;

glRotatef(xRotation, 1.0f, 0.0f, 0.0f);
glRotatef(yRotation, 0.0f, 1.0, 0.0f);
glRotatef(zRotation, 0.0f, 0.0f, 1.0f);

[mesh render];

//restore the matrix
glPopMatrix();

}

This code works correctly and the object rotates around the center. The problem is that I also have a matrix which defines the starting position of the object in the scene called matricesArray. I added a new line to my code to multiply by this matrix and place the object in its correct starting position :

-(void)render
{
// clear the matrix
glPushMatrix();
glLoadIdentity();

// move to my position

//xRotation = 280;

//scale
glScalef(0.000015, 0.000015, 0.000015);

xRotation =280.0;
zRotation =1.0;
yRotation +=0.5;

glRotatef(xRotation, 1.0f, 0.0f, 0.0f);
glRotatef(yRotation, 0.0f, 1.0, 0.0f);
glRotatef(zRotation, 0.0f, 0.0f, 1.0f);

glMultMatrixf(matricesArray);  //This is the line I have added to apply the matrix.

[mesh render];

//restore the matrix
glPopMatrix();


}

The problem is that the object now rotates in a wide circle around the screen.

My question is what is the correct order to apply the matrix in my code ?

Thank you in advance.

Answer 1

You need to first rotate then translate to the location you want it to be.