Mathmatics

SDL Development
1

I am searching somebody that could explain me how to use a rotation matrix
on a Surface to make 2D rotations.
I know a lib called SGE that implements this features, but I want to learn
how to do it myself.

And if somebody have URL, I would agree too :)) .

bye bye

2

Err, it’s not strictly an SDL question, but maybe this’ll get you
started …

given point x, y (rotating about the origin):

new_x = x * cos(angle) - y * sin(angle);
new_y = x * sin(angle) + y * cos(angle);

it’s not using a matrix of any sort but that’s the math to rotate a
single point around the origin, which i used to make a simple rotate
surface function. also, this way requires some simple anti-aliasing as
the math doesnt correctly fill in rotated images (you end up w/ "holes"
in ur rotated images).

that help at all?On Tue, 2002-08-20 at 02:30, carlos wrote:

I am searching somebody that could explain me how to use a rotation matrix
on a Surface to make 2D rotations.
I know a lib called SGE that implements this features, but I want to learn
how to do it myself.

And if somebody have URL, I would agree too :)) .

bye bye

3

Here’s URL:

http://mathworld.wolfram.com/RotationMatrix.html

I hope it helps.
JacekOn Tue, Aug 20, 2002 at 11:30:09AM +0200, carlos wrote:

I am searching somebody that could explain me how to use a rotation matrix
on a Surface to make 2D rotations.
I know a lib called SGE that implements this features, but I want to learn
how to do it myself.

And if somebody have URL, I would agree too :)) .

–
±------------------------------------+
|from: J.C.Wojdel |
| J.C.Wojdel at cs.tudelft.nl |
±------------------------------------+

4

Here’s URL:

http://mathworld.wolfram.com/RotationMatrix.html

Here’s another one that looks good at a glance:

http://www.makegames.com/3drotation/

Google is overflowing with good information on this.

–ryan.