Rotating points in 3D

I am working with some vector graphics that consists only of an ordered set of 2D points in XY space. The order of points determines the path that a line is drawn through them.

I would like to be able to rotate the points in 3D so that I can flip and rotate the vector picture. After performing a rotate of some degree I want to be able to write the new set of points to an array or file or whatever. I also want to be able to display my vector image in a Window.

So I have two questions:

1) Is there anything in DirectX that will help me rotate some XY points in a 3D space and then give me the resulting XY coordinates

2) What do I use to draw these points to the Window using DirectX In the past I have used normal Windows drawing methods but they are slow.

Detailed answers are not needed at this point. If you can point me to some DirectX classes that would help or some samples that would be a great start.

Thanks,

Gary

Thanks for the lead. I will look into those and see how far I can get.

Gary

OK. I didn't get very far. I see those transform functions require a transform matrix as a parameter but I don't remember much about matrices from college. :) Could you help me out with some examples Lets say I want to rotate around X by 10 degrees, what matrix would I use What about for Y and Z What if I wanted to move it 10 steps to the left

Thanks again

Gary

Now you've got math basis, you can have a look to the D3DX math function in the sdk documentation. See for exemple D3DXMatrixRotationZ that will create a rotation matrix an an angle in radian around Y axis. That's all you need, isn't it Then, you can compose matrix transformations using D3DXMatrixMultiply and soon you'll be matrix ready!

Have a try with those functions and I'm sure you'll get your results soon.

If you need some more math, see The Matrix and Quaternions FAQ which is always helpful.

Saliksyed,

Please excuse my ignorance but would you mind running through an example using cartesian coords so I can visualize the solution

I'm just trying to understand the process/math so if you could skip any D3D function calls I would appreciate it :-)

How would I rotate a point that lies at -say 2,4,6 about another point say 10,12,14 (on an axis parallel to the X axis) by 25 degrees

Thanks

Scott

This article should probably help you out:

http://msdn.microsoft.com/library/default.asp url=/library/en-us/directx9_m/directx/direct3d/gettingstarted/transforms/matrices/matrices.asp

Hope that helps. Happy Holidays

Scott,

So to elaborate on an explanation of how to do the scenario that you layed out, here is my 2 cents:

You should keep in mind that anytime you are rotating you pay attention to the order of mulitiplication of matrices as this affects which origin you are rotating about (ie. model space or world space). With that being said, after you have built your object and are ready to rotate it about a known vertex you would do this:

// setup global variables
D3DXMATRIX mtxPitch;

// setup point to rotate around
D3DXVECTOR3 rotationVectorAxis(10.0f, 0.0f, 0.0f);

// rotate this amount
float RotationPitch = D3DXToRadian(2.5f);

// build rotation matrix
D3DXMatrixRotationAxis(&mtxPitch, &rotationVectorAxis, RotationPitch);

// apply rotation to object's matrix (world)
D3DXMatrixMultiply(&object.mtxWorld, &object.mtxWorld, &mtxPitch);

To explain more of what is going on is to understand how rotations with matrices works:
(where O = radians of rotation)

X Axis Rotation:

1 0 0
0 cos(O) sin(O) New Y Coord = Old Y Coord x cos(O) - Old Z Coord x sin(O)
0 -sin(O) cos(O) New Z Coord = Old Y Coord x sin(O) + Old Z Coord x cos(O)

Y Axis Rotation:

cos(O) 0 -sin(O) New X Coord = Old X Coord x cos(O) + Old Z Coord x sin(O)
0 1 0
sin(O) 0 cos(O) New Z Coord = Old X Coord x -sin(O) + Old Z Coord x cos(O)

Z Axis Rotation

cos(O) sin(O) 0 New X Coord = Old X Coord x cos(O) - Old Y Coord x sin(O)
-sin(O) cos(O) 0 New Y Coord = Old X Coord x sin(O) + Old Y Coord x cos(O)
0 0 1

Hope this helps!

Cale