# matrixes for objects in a 3D world?

If i want to make a 3d world with objects that can rotate around their own axises do each of the objects have to have their own private rotation-matrix if i want them to be displayed correctly?

or is there a simpler way using glRotate?

correct me if i’m wrong but glRotate only rotates the object around the camera-axises

and do they all maybee need a position-matrix too?

i want all my objects to be able to move and rotate around their own x-axis y-axis and z-axis

Look at the 4th NeHe Tutorial, titled ‘Rotation’.

and in his tutorial they rotate the object around the world axis.

his tutorials doesn’t really cover object space orientations.

and he has only one object and a camera there

i want to make 3d world with multiple objects and multiple cameras.

so whats the easiest way to make an object rotate and move along its own axises?

hmm i just found out about Quaternion’s ill look into that.

Okay so i made every object with a rotation matrix and a position matrix and it works, without using quarternions. Here some code if anyone is interested. Took me a while to figure this out.

``````
void moveX(float v){ // any object x axis movement
glPushMatrix();
glTranslatef(rotationMatrix[0]*v,rotationMatrix[4]*v,rotationMatrix[8]*v);
glGetFloatv(GL_MODELVIEW_MATRIX,positionMatrix);
glPopMatrix();

}
void rotateX(float v){ //any object x axis rotation
glPushMatrix();
glRotatef(v,rotationMatrix[0],rotationMatrix[4],rotationMatrix[8]);
glGetFloatv(GL_MODELVIEW_MATRIX,rotationMatrix);
glPopMatrix();
}

void setView(){// camera
glMatrixMode(GL_MODELVIEW); // Select The Modelview Matrix
glMultMatrixf(positionMatrix);
//wrong implementation might have the inverse effect
//rotate first move second will cause the fps effect
//move first rotate second will cause the fixed camera effect
//all other models will/should draw with the camera matrix defaults added to them
}

void draw(){ // model
glPushMatrix();
glMultMatrixf(positionMatrix);
glMultMatrixf(rotationMatrix);

glColor4f(red,green,blue,alpha);
glBindTexture(GL_TEXTURE_2D, texture[0]);

glTexCoord2f(0.0f, 0.0f); glVertex3f(-scale,-scale,-scale);
glTexCoord2f(0.0f, 1.0f); glVertex3f(-scale,-scale,+scale);
glTexCoord2f(1.0f, 1.0f); glVertex3f(-scale,+scale,+scale);
glTexCoord2f(1.0f, 0.0f); glVertex3f(-scale,+scale,-scale);

glTexCoord2f(0.0f, 0.0f); glVertex3f(+scale,-scale,-scale);
glTexCoord2f(0.0f, 1.0f); glVertex3f(+scale,-scale,+scale);
glTexCoord2f(1.0f, 1.0f); glVertex3f(+scale,+scale,+scale);
glTexCoord2f(1.0f, 0.0f); glVertex3f(+scale,+scale,-scale);

glTexCoord2f(0.0f, 0.0f); glVertex3f(-scale,-scale,-scale);
glTexCoord2f(0.0f, 1.0f); glVertex3f(-scale,-scale,+scale);
glTexCoord2f(1.0f, 1.0f); glVertex3f(+scale,-scale,+scale);
glTexCoord2f(1.0f, 0.0f); glVertex3f(+scale,-scale,-scale);

glTexCoord2f(0.0f, 0.0f); glVertex3f(-scale,+scale,-scale);
glTexCoord2f(0.0f, 1.0f); glVertex3f(-scale,+scale,+scale);
glTexCoord2f(1.0f, 1.0f); glVertex3f(+scale,+scale,+scale);
glTexCoord2f(1.0f, 0.0f); glVertex3f(+scale,+scale,-scale);

glVertex3f(-scale,-scale,-scale);
glVertex3f(-scale,+scale,-scale);
glVertex3f(+scale,+scale,-scale);
glVertex3f(+scale,-scale,-scale);

glVertex3f(-scale,-scale,+scale);
glVertex3f(-scale,+scale,+scale);
glVertex3f(+scale,+scale,+scale);
glVertex3f(+scale,-scale,+scale);
glEnd();

glPopMatrix();
}

``````

I used opengl built in matrix operations which gives a really bad cpu performance. I’ll fix my own matrix operation classes later.
glGetFloatv(); is the one causing heavy cpu drain.

you could concatenate them directly without glGet. all query functions should be avoided and called only at startup/loading times. best to you use own matrix classes and glLoadMatrix them, which is also the only way for OpenGL 3.0 afaik.