You can use a rotation matrix to rotate a vector (or another matrix). a point (x, y) in an image is a vector.
A 2d rotation matrix looks like this:
[a, b]
[c, d] where a = cos a#, b = -sin a#, c = sin a#, d = cosa#
(a# = alpha = the angle)
To rotate a vector you multiply the matrix with the vector, which is simplified to:
x_new = x_old * a + x_old * c
y_new = y_old * b + y_old * d
This will rotate the image around the center, but you need to decide the size of the new image before starting to write pixels to it, so using Newton's handler saves you some hazzle.
-A.
Matrix, matrix...hum... kan you develop a bit more?
or any place where i can find a tut on this?
Fabrice
Andreas Gaunitz P11 heeft op donderdag 12 december 2002 om 15:29 het volgende geschreven:
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now, for the second composite i need to rotate the text info before making the composite.
how do i do this?
Fabrice
Use a little matrix maths and a 2d rotation matrix?
-A.
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