Hi everyone In my ( very ) little 3D engine i use AABBs, which are represented by a minimal and a maximal Vector of the object they surround. CVector3 m_vMin; Cvector3 m_vMax; As long an object is centered around the origin, the corresponding bounding Box is drawn correctly. However, if i translate the object via glTranslatef ( 0.0f, 0.0f, 10.0f ) the Bounding Box is still drawn as if the object was around the origin. The Bounding Box doesn't get translated. In order to translate the min and max Vectors, i call glGetFloatv (GL_MODELVIEW_MATRIX, mvMatrix); and then i add the 4th row of the given matrix to m_vMin and m_vMax ( mvMatrix Indices 3,7 and 11 ). Am i using the wrong matrix ? Because, if i start my debugger with a breakpoint directly after the above "glGetFloatv" call, i can see that the forth row of mvMatrix is ( 0,0,0,1 ). Shouldn't it be something like ( 0,0,10,1 ) o_0 ? The results i get when i use rotation are even more weird .... I guess i am making a terrible obvious mistake. But which one ? Thanks for any help.

Apply exactly the same translations to your bounding box (ie yoiur min max variables) as you do to the model.

You are accessing the wrong indices. OpenGL store matrices in column-major format:

 0  4  8 12 1  5  9 13 2  6 10 14 3  7 11 15

So you actually want indices 12, 13 and 14, not 3, 7, and 11.

Enigma

Thanks for the answers ! I actually assumed that opengl Matrices are row-major matrices. However, it still doesn't work right, and i think it has something to do with the order i call the commands
Here is how i do it:


renderscene
{
glLoadIdentity();

gluLookAt( g_Camera.m_vPosition.x , g_Camera.m_vPosition.y , g_Camera.m_vPosition.z,
g_Camera.m_vView.x , g_Camera.m_vView.y , g_Camera.m_vView.z ,
g_Camera.m_vUp.x , g_Camera.m_vUp.y , g_Camera.m_vUp.z );


/* draw the AABB of the object, according to the transformed coordinates,
* which were calculated by the last object.m_AABB.recalculate call ( see below )
*/

object.m_AABB.draw();

// Apply Translation
glTranslatef( 0.0f, 0.0f, 10.0f);

// Recalculate the min and max Vektor of the aabb
object1.m_AABB.recalculate();

// Draw the object
object.draw();


SDL_GL_SwapBuffers( );

}

The AABB isn't drawn were it should: It moves as i move the camera. Any hints ? How are you doing AABB recalculation after an object transformation ?