View Full Version : Get cube points after transformations

Barbarosa

06-30-2013, 04:23 PM

Hello,

I have created a cube (with known vertices) and i rotate and traslate it. What i lack are the new positions of its vertices after the transformations. So the question is do i have to find the transformation matrix on paper in order to calculate the vertices, or there is some function to get them?

Thanks in advance

tonyo_au

06-30-2013, 11:42 PM

Why do you need the translated vertices?

Barbarosa

07-01-2013, 02:06 AM

I try to implement the separating axis theorem for some oriented bounding boxes (cubes in my case). So i need the unit vectors that represent the 3 local axis of each box. To find these unit vectors i subtract the vertices to get the vectors and then i normalize them. And that's where i stuck because i have to know the positions of the vertices after the transformations.

Carmine

07-01-2013, 10:52 AM

... i have to find the transformation matrix on paper in order to calculate the vertices, or there is some function to get them? Here's an example of how I do it using fixed pipeline OpenGL commands only.

void Retrieve_Transformed_Vector (void)

{

glMatrixMode (GL_MODELVIEW);

glLoadIdentity ();

// same modeling transformations that are applied to cube go here.

glTranslatef (corner[0], corner[1], corner[2]);

glGetFloatv (GL_MODELVIEW_MATRIX, transmat); // read manual on transmat, should be a GLfloat transmat[16]

// transmat[12],[13],[14] are the new coordinates of corner

}

Barbarosa

07-01-2013, 05:02 PM

That's exactly what i was looking for. Thank you very much!

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