BorlandTalk.com

Jon Lennart Aasenden · Guest

How hard is it to rotate a point in 3d space in pure delphi?

Say a dot: -10,-10,10
and i want to rotate the values -40 on the z axis? (thats left and down is
it not)

I seem to remember the formula for 3d was: result:=(x * y) / depth?

Any info is welcome
Just want to code the old rotating, non-filled, line cube that was so cool
on the amiga back in the 80'ies

Jon Lennart Aasenden,
Norway

Andi · Guest

Your dot has 3 coordinates: (-10, -10, 10). After rotating it around
whatever axis it has still 3 coords. The formula you gave returns only one
value. What you need is a set of 3 formulas giving you 3 new coords of your
dot. These 3 formulas envolve (if you want to rotate by arbitrary degrees)
the sin and cos functions.

For 2D rotation (with 2 coords xold and yold) these formulas are:

xnew := xold*cos(angle) - yold*sin(angle);
ynew := xold*sin(angle) + yold*cos(angle);

In 3D rotation things become a lot more tricky because it depends on the
order in which you perform the rotations around the 3 axes: first around x,
then y, then z? If you change this order your dot will finally have a
different global position! If you want to do some research on this look for
"Euler angles".

"Jon Lennart Aasenden" <post_nospam_nojunk (AT) hexmonks (DOT) net> schrieb im
Newsbeitrag news:408dae06 (AT) newsgroups (DOT) borland.com...

Rene Tschaggelar · Guest

Jon Lennart Aasenden wrote:

Jon Lennart Aasenden · Guest

Thanks for the tips :)

But i wanted native delphi 3d code, not opengl or directx :)

Jon Lennart Aasenden

"Rene Tschaggelar" <ee123123wqe12 (AT) sd242323 (DOT) com> wrote

Guest · Posted: Tue Apr 27, 2004 10:13 pm Post subject: Re: old school 3d

impressive:
http://www.geocities.com/peter_bone_uk/engine3d.html

"Jon Lennart Aasenden" <post_nospam_nojunk (AT) hexmonks (DOT) net>

Jon Lennart Aasenden · Guest

thanks!

Jon Lennart Aasenden

<tt (AT) atonline (DOT) de> wrote

Nils Haeck · Guest

Your formula (although wrong) seems to refer to the perspective projection.

In a 3D transformation, your point goes to a new 3D point, so it still has 3
coordinates. When doing the final transformation towards the screen, the Z
is usually disregarded, or simply used to scale the other axes.

You can use quaternions or Euler angles to do the rotation of 3D points, and
combine the resulting matrices for scaling, translation and rotation into
one transformation matrix (3x3).

Nils

"Jon Lennart Aasenden" <post_nospam_nojunk (AT) hexmonks (DOT) net> wrote