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# matrix transposition and translation vector

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### #1giugio  Members   -  Reputation: 207

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Posted 09 July 2012 - 08:10 AM

Hy.
I have a scenegraph.
Each object in the scenegraph is a node and can have a parent(1 or 0 ) for my application i must multiply from the bottom to the top.
Each node have a 3x3 rotation matrix and a 3dvector for the traslation.
I can do node->parent for find the parent node.
i use a loop for iterate from bottom to top and use the parent() function.

1)i do in the loop: currentMatrix =currentNode->parent()->getmatrix3x3->Trasposed() * currentMatrix
then the currentNode becomes : currentNode = currentNode->parent() until the parent == 0.
2)first problem : how i must multiply the translation vectors where each node is? At each position i must draw a mesh , then i must have the correct location.

3)I must use transposed matrix for my project , is correct do the transposition every cicle only for the new matrix?like
currentNode->parent()->getmatrix3x3->Trasposed() * old concatenate matrix?

thanks.

Edited by giugio, 09 July 2012 - 08:11 AM.

### #2Faelenor  Members   -  Reputation: 381

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Posted 09 July 2012 - 11:22 AM

Why don't you use 4x4 matrices? You would have your translation in the matrix and computed with the multiplication.

If you have to multiply by the transpose, create a multTranspose kind of method instead of using a temporary transposed matrix object. You don't need this object, you just have to multiply the matrix components in the transposed direction.

Finally, when you traverse you tree, you can keep a pre-multiplied matrix of all the node from the parent to the root, to avoid your costly loop.

Edited by Faelenor, 09 July 2012 - 11:23 AM.

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