matrixes for objects in a 3D world?

OpenGL OpenGL: Basic Coding
1

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

2

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

3

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?

4

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

5

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();
        glLoadMatrixf(positionMatrix);
        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();
        glLoadMatrixf(rotationMatrix);
        glRotatef(v,rotationMatrix[0],rotationMatrix[4],rotationMatrix[8]);
        glGetFloatv(GL_MODELVIEW_MATRIX,rotationMatrix);
    glPopMatrix();
}

void setView(){// camera
    glMatrixMode(GL_MODELVIEW); // Select The Modelview Matrix
    glLoadMatrixf(rotationMatrix);
    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]);

            glBegin(GL_QUADS);
                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.

6

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.