switching from third person view to first person view

Question

I have done a scene in opengl where I'm using a third person camera (that I can control with the mouse). Then, inside it, it has the camera of the first view (that I called thirdpersonCamera, see the code above), drawing the camera, the frustum etc..

It looks like this picture:

and I've done with this code:

void GLView::drawSubThirdpersoncamera()
{
    // set perspective viewing frustum in the 3rd person camera
    thirdpersonCamera.setFrustum(FOV_Y, (float)(W)/(H), NEAR, FAR);

    // use 3rd person camera projection matrix (the frustum, the perspective etcetera)
    // as the opengl camera
    glMatrixMode(GL_PROJECTION);
    glLoadMatrixf(thirdpersonCamera.projectionMatrix.getTranspose());
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();

    glPushMatrix();
    {
        // First, transform the camera (viewing matrix) from world space to eye space
        glLoadMatrixf(thirdpersonCamera.viewMatrix.getTranspose());

        // translate and rotate the mouse control
        // (keeping the camera fixed because
        // we want only the scene to rotate/translate)
        // for thinking about modern opengl: should be a matrix..
        glTranslatef(mousePosition[0], mousePosition[1], mousePosition[2]);
        glRotatef(mouseAngle[0], 1, 0, 0); // pitch
        glRotatef(mouseAngle[1], 0, 1, 0); // heading
        glRotatef(mouseAngle[2], 0, 0, 1); // roll

        // now the draw the scene
        drawScene();

        // draw the first person camera
        glPushMatrix();
        {
            glMultMatrixf(physicalCamera.viewMatrix.getTranspose());

            drawAxis(4);
            drawCamera();
            drawFrustum(physicalCamera.fovy, physicalCamera.aspectRatio, physicalCamera.near, physicalCamera.far);
        }
        glPopMatrix();

    }
    glPopMatrix();
}

Now I want to switch to the eye of the camera I've drawn, with this code:

void GLView::drawSubPhysicalCamera()
{
    // use physical camera projection matrix (the frustum, the perspective etcetera)
    // as the opengl camera
    glMatrixMode(GL_PROJECTION);
    glLoadMatrixf(physicalCamera.projectionMatrix.getTranspose());
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();

    glPushMatrix();
    {
        // the view matrix: how the camera is positioned in the world space
        glLoadMatrixf(physicalCamera.viewMatrix.getTranspose());

        drawScene();
    }
    glPopMatrix();

}

I think it should go because I'm using the same matrix once for translate the object in the screen, once for translate the camera but.. in the second view I don't see anything.. I don't find any error because the transformation in the space is the same but.. it doen't work..

Where am I wrong?

Answer 1

As clearly explained in this article I have to take the inverse:

If you only have the view matrix and you need to find a camera transform that can be used to position a visual representation of the camera in the scene, you can simply take the inverse of the view matrix.