plib-users

Re: [Plib-users] DXF loader

[Steve B. <sjb...@ai...>]

saul leite wrote:

>   I tried to load DXF files that I create using that Blender modeler, and my files were
> not being loaded properly.

Could you be a little more specific?   Are there error messages?   Does the program crash?
Does it load *anything* visible at all?  What are the problems?

It's impossible to diagnose without a bit more information!

> I tried using Pretty Poly to open DXF files created using blender and it doesnt work either.

Prettypoly and PLIB use the same file loaders - so what works for one works for the other.

>   I really like to use blender, and DXF is the only export format it has. Has anyone
> else used DXF files? Could this be a bug in PLIB or Blender?

It could be in either...or simply a limitation of DXF that it can't represent
everything that was in your model.

Without some more information, we can't help.

Can you put the model up on a web site somewhere where we can download it?

----------------------------- Steve Baker -------------------------------
Mail : <sjb...@ai...>   WorkMail: <sj...@li...>
URLs : http://www.sjbaker.org
       http://plib.sf.net http://tuxaqfh.sf.net http://tuxkart.sf.net
       http://prettypoly.sf.net http://freeglut.sf.net
       http://toobular.sf.net   http://lodestone.sf.net

[Plib-users] CVS snapshot

[Norman V. <nh...@ca...>]

Hi All

It appears as if the cron daemon is having problems
creating the daily CVS snapshot,  current.tgz.  

The last snapshot was created on Dec 22 2001
and is what is currently available at the usual URL
< linked as 'current.tgz' from PLib 'download page' >

Hopefully this is a minor issue with SourceForge that
may perhaps be related to possibly reduced staffing 
levels during the holidays.   

I am investigating further

Cheers

Norman

Re: [Plib-users] DXF loader

[Wolfram K. <w_...@rz...>]

You wrote:

>Hello,
>
>  I tried to load DXF files that I create using that Blender modeler, =
and my files were not being loaded properly. I tried using Pretty Poly to=
 open DXF files created using blender and it doesnt work either.
>
>  I really like to use blender, and DXF is the only export format it =
has. Has anyone else used DXF files? Could this be a bug in PLIB or =
Blender?

If you want, you can send me the model. AFAIk, DXF loading should
work. I am pretty sure that people have also exported VRML or a
similar format from blender and got that into ssg/PLIB.

Bye bye,
Wolfram.

[Plib-users] DXF loader

[saul l. <le...@en...>]

Hello,

  I tried to load DXF files that I create using that Blender modeler, and my files were not being loaded properly. I tried using Pretty Poly to open DXF files created using blender and it doesnt work either.

  I really like to use blender, and DXF is the only export format it has. Has anyone else used DXF files? Could this be a bug in PLIB or Blender?
-- 

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RE: [Plib-users] Window (x,y) to world coordinates

[Norman V. <nh...@ca...>]

Steve Baker writes:
>
>Ask For Joy wrote:
>
>> What I am looking for is a way to translate window coordinates obtained
from the
>> mouse to world coordinates, taking into account the window dimensions and
>> current camera position.
>
>Well, you can't do that for an arbitary setup - because there are an
infinite
>number of world coordinates that lie in a line from your eye through the
mouse
>position and out into the world.
>
>However, if you just want to know where it hit your XY plane
>(or any other specific plane for that matter) then you need to do this:

>There are SG routines for all of those separate operations - but no single
>function to do the entire thing (that I'm aware of).
>
>If some kind soul were to write such a thing, it would be cool
>to put it into the SSG camera class.

I believe PPE contains a 'generic' function that can be adapted for this

ppe / src / viewer / ppeViewerDraw.cxx
void ppeViewer::update_3D_cursor ( sgVec2 mouseXY )
 and just use the
    case FOLLOW_PLANE :
  code block

I believe the only necessary data external to the function will be
the window width and height
the camera orientation (hpr)
and the sgVec4 plane we want to report our position on

in this case I believe
the camera is [0, 90, 0 ]
and the plane is  [ 0, 0, 1, 0 ]
so all Joy needs is the window width and height

Cheers

Norman

Re: [Plib-users] Window (x,y) to world coordinates

[Steve B. <sjb...@ai...>]

Ask For Joy wrote:

> I have a PLIB application in which my camera is facing down along the Z axis to
> look at a grid on the XY plane.  I can move the camera up and down along the Z
> axis to effectively 'zoom' my view of the plane.

(Technically, that's not "zooming" - you have to change the camera's field of
view to make it zoom).

>  I can also move the camera
> along the XY axis, but in all cases I am looking down square upon the XY axis .

That's probably because SG & SSG use a 'Z-is-up' coordinate system so the default
camera is looking along the Y axis towards Y==+infinity.

If you made your XY grid in a 3D modelling program then it's probably built
using Y-is-up and our model loaders will have switched the coordinates around
for you so it's now an XZ grid.  Now, it's a vertical wall and we are staring
straight at it.  When you move the camera in Z, you are getting higher in
altitude - which I think explains what you are seeing.

Of course this is all blown away as an explanation if you typed the grid into
your C++ code and stuffed the coordinates directly into SSG.

(Yes, I know that OpenGL uses Y-is-up - but I come from a flight simulation
background and we've always used Z-is-up.  When I wrote SSG, I didn't really
intend for anyone else to ever use it - so I wrote it for *MY* personal
convenience...it doesn't matter at all in terms of functionality - but it
can be a little confusing for beginners and people who use Y-is-up routinely.)

> What I am looking for is a way to translate window coordinates obtained from the
> mouse to world coordinates, taking into account the window dimensions and
> current camera position.

Well, you can't do that for an arbitary setup - because there are an infinite
number of world coordinates that lie in a line from your eye through the mouse
position and out into the world.

However, if you just want to know where it hit your XY plane (or any other specific
plane for that matter) then you need to do this:

  Figure out where the 'camera' is in your world.
  Imagine that this is really where your eye is.
  Imagine the screen sitting in your scene at an appropriate
    distance and direction from your eye for the field of view
    that you selected.
  Imagine the mouse cursor stuck onto that little rectangle.
  Draw a line from the eye, through the tip of the mouse out into
    the scene.
  Figure out where that line intersects your infinite plane...that's
     the coordinate you need.

The routine:

  sgIsectInfLinePlane ( sgVec3 dst,
                        sgVec3 l_org, sgVec3 l_vec,
                        sgVec4 plane ) ;

...computes the intersection of an infinite line with an infinite plane.

So 'dst' will be populated with the results.
   'l_org' is the origin of your line (which in this case is
   the position of the camera (your eye) in the scene.
   'l_vec' is a unit vector pointing in the direction of the
   line.  This is going to be defined by the mouse position
   rotated by the camera rotation.
   'plane' is the plane equation of your infinite plane (you can
   form the plane equation directly if you know what you are doing - if
   not, pass three points from the plane into sgMakePlane and it'll
   figure out the plane equation for you).

The hardest part of this is getting the 'l_vec' thing right.  The
easy way is to create a 3D point that represents the mouse coordinate...
so if the mouse is at:  ( mx, my )  then in 3D, it's at ( mx, screendist, my )
(remembering that Z-is-up in PLIB - and assuming your mouse coordinates are
(0,0) in the center of the screen with Y getting bigger towards the top of
the screen and X getting bigger to the right).

The 'screendist' thing is the distance of the screen from your eye. 
You have to figure that out using the field of view angle and some
simple trig..

   screendist = (screen_width/2) / tan ( horizontal_fov / 2 )

(Notice that the 'screen_width' term has to be in the same units as
your mouse coordinates).

*PHEW* nearly there!

Now you have to transform the 3D mouse coordinate by the current camera
(modelview) matrix to get it's position in World coordinates.  Now subtract
the eyepoint position in the world to get a vector - normalize it to get
a unit vector.  Now you have everything you need to call sgIsectInfLinePlane.

One slight 'gotcha' is that when you are flying over your infinite 'ground'
plane, you might point the mouse up into the 'sky' where it doesn't hit
the plane at all...well, actually it does because sgIsectInfLinePlane
intersects an INFINITE line - it's infinite in both directions so what you'll
actually get under these circumstances is a 'hit' on the 'ground' somewhere
behind the camera.  What you want to do under these circumstances depends
on your application.

There are SG routines for all of those separate operations - but no single
function to do the entire thing (that I'm aware of).

If some kind soul were to write such a thing, it would be cool to put it
into the SSG camera class.

> Is there an easy formula or matrix operation in PLIB
> that will allow me to do this?  I tried playing around with the ortho matrix,
> but my experimentation didn't get me very far.

Easy is a relative term...

In a program like PrettyPoly (http://prettypoly.sf.net), we do this by intersecting
a ray from the eye out through the mouse cursor and figuring out which polygon
it struck.  Then we can find the plane equation of that polygon and figure out
where it was hit.  That removes the limitation of only hitting a single plane -
but it's *MUCH* more complicated.  We actually use OpenGL's 'pick' feature to
find out what we clicked the mouse on - there is special support for that in
SSG - but since PPE is the one thing it was written for, the documentation
is pretty much absent.

> BTW, PLIB is wonderful.  Its very gradual learning curve and intutitive
> interface is the main reason why I switched back from Direct3D to OpenGL for my
> application.

<blush>

----------------------------- Steve Baker -------------------------------
Mail : <sjb...@ai...>   WorkMail: <sj...@li...>
URLs : http://www.sjbaker.org
       http://plib.sf.net http://tuxaqfh.sf.net http://tuxkart.sf.net
       http://prettypoly.sf.net http://freeglut.sf.net
       http://toobular.sf.net   http://lodestone.sf.net

[Plib-users] Window (x,y) to world coordinates

[Ask F. J. <ask...@ya...>]

Hello all,

I have a PLIB application in which my camera is facing down along the Z axis to
look at a grid on the XY plane.  I can move the camera up and down along the Z
axis to effectively 'zoom' my view of the plane.  I can also move the camera
along the XY axis, but in all cases I am looking down square upon the XY axis .

What I am looking for is a way to translate window coordinates obtained from the
mouse to world coordinates, taking into account the window dimensions and
current camera position.  Is there an easy formula or matrix operation in PLIB
that will allow me to do this?  I tried playing around with the ortho matrix,
but my experimentation didn't get me very far.

BTW, PLIB is wonderful.  Its very gradual learning curve and intutitive
interface is the main reason why I switched back from Direct3D to OpenGL for my
application.

Thanks for your help,
Aaron [ask...@ya...]



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Re: [Plib-users] ssgLoadBGL

[Steve B. <sjb...@ai...>]

Tengchiang Tsao wrote:

> > it's released under the BSD license without the
> > advertising clause:
> 
> Does that mean we can use their code willingly as long
> as we put the BSD copy right statement header on top
> of the files? Then we need to put GPL satement below
> or on top of the original BSD statement?

The BSD license is pretty liberal - it basically says that
you have to preserve the copyright message - but that's
about all.

I don't see a problem with putting it into PLIB - but you should
certainly email it's author and ask nicely.


----------------------------- Steve Baker -------------------------------
Mail : <sjb...@ai...>   WorkMail: <sj...@li...>
URLs : http://www.sjbaker.org
       http://plib.sf.net http://tuxaqfh.sf.net http://tuxkart.sf.net
       http://prettypoly.sf.net http://freeglut.sf.net
       http://toobular.sf.net   http://lodestone.sf.net

Re: [Plib-users] ssgLoadBGL

[Sebastian U. <ud...@ha...>]

On Mon, 17 Dec 2001, ten...@ya... (Tengchiang Tsao) wrote:
> Date: Mon, 17 Dec 2001 09:32:26 -0800 (PST)
> To: pli...@li...
> From: ten...@ya... (Tengchiang Tsao)
> Subject: Re: [Plib-users] ssgLoadBGL

[...]

> > Steve,
> > 
> > it's released under the BSD license without the
> > advertising clause:
> 
> Does that mean we can use their code willingly as long
> as we put the BSD copy right statement header on top
> of the files? Then we need to put GPL satement below
> or on top of the original BSD statement?

I guess so.


- Sebastian

Re: [Plib-users] ssgLoadBGL

[Tengchiang T. <ten...@ya...>]

--- Sebastian Ude <ud...@ha...> wrote:
> 
> 
> On Sun, 16 Dec 2001, sjb...@ai... (Steve
> Baker) wrote:
> > Date: Sun, 16 Dec 2001 13:39:16 -0600
> > To: Tengchiang Tsao <ten...@ya...>
> > From: sjb...@ai... (Steve Baker)
> > CC: pli...@li...
> > Reply-To: sjb...@ai...
> > Subject: Re: [Plib-users] ssgLoadBGL
> > 
> > Tengchiang Tsao wrote:
> > > 
> > > Hi,
> > >   This is Tengchiang Tsao. I am modifying scdis
> > > (http://www.freesc.org) to make ssgLoadBGL.
> > 
> > It's not clear what license SCDIS is under -
> contributions
> > to PLIB have to be licensable under LGPL - please
> check that
> > this is OK before you do any more!
> 
> Steve,
> 
> it's released under the BSD license without the
> advertising clause:

Does that mean we can use their code willingly as long
as we put the BSD copy right statement header on top
of the files? Then we need to put GPL satement below
or on top of the original BSD statement?

Tengchiang


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Re: [Plib-users] ssgLoadBGL

[Tengchiang T. <ten...@ya...>]

--- Wolfram Kuss <Wol...@t-...> wrote:
> Hi,
> 
> A BGL loader, especially one that loads the geometry
> and not just the 
> position of buildings would be *very* welcome. I
> second everything
> Steve said. I think you should e-mail the author of
> scdis anyway.
> 
> Even though it is binary, building on ssgLoadMDl
> might make sense,

As for me, a beginer, rewriting ssgLoadBGL by
utilizing scdis is more attractive than adding code to
ssgLoadMDL. 

If I am not allowed (which seems to be true) to open
any binary file viewer and need to improve ssgLoadMDL
to read more BGL files, all I can think of is
rewriting ssgLoadBGL by utilizing scdis. 

This is the advantage of open source! We save our time
and effort to the minute.

So far, I can load only 10% of bgl scenery from
www.flightsim.com with my modified version of
ssgLoadMDL

Tengchiang


> since the actual BGL code inside is the same, AFAIK
> it is just in
> another section. With gmax, creating a MDL or a BGL
> is just one switch
> while saving (and you have to input the lat/lon when
> saving a BGL).
> 
> >  Are there any other loader projects on going?
> 
> AFAIK no one is working on a new loader. I made some
> improvements on
> the MDL loader, but it can't load MSFS 2002 files
> yet.
> 
> >Tengchiang Tsao
> 
> Bye bye,
> Wolfram.
> 
> _______________________________________________
> plib-users mailing list
> pli...@li...
>
https://lists.sourceforge.net/lists/listinfo/plib-users


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Re: [Plib-users] ssgLoadBGL

[Sebastian U. <ud...@ha...>]

On Sun, 16 Dec 2001, sjb...@ai... (Steve Baker) wrote:
> Date: Sun, 16 Dec 2001 13:39:16 -0600
> To: Tengchiang Tsao <ten...@ya...>
> From: sjb...@ai... (Steve Baker)
> CC: pli...@li...
> Reply-To: sjb...@ai...
> Subject: Re: [Plib-users] ssgLoadBGL
> 
> Tengchiang Tsao wrote:
> > 
> > Hi,
> >   This is Tengchiang Tsao. I am modifying scdis
> > (http://www.freesc.org) to make ssgLoadBGL.
> 
> It's not clear what license SCDIS is under - contributions
> to PLIB have to be licensable under LGPL - please check that
> this is OK before you do any more!

Steve,

it's released under the BSD license without the advertising clause:

http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/*checkout*/freesc/scdis/src/type.h?rev=1.14


- Sebastian

Re: [Plib-users] ssgLoadBGL

[<Wol...@t-...>]

Hi,

A BGL loader, especially one that loads the geometry and not just the=20
position of buildings would be *very* welcome. I second everything
Steve said. I think you should e-mail the author of scdis anyway.

Even though it is binary, building on ssgLoadMDl might make sense,
since the actual BGL code inside is the same, AFAIK it is just in
another section. With gmax, creating a MDL or a BGL is just one switch
while saving (and you have to input the lat/lon when saving a BGL).

>  Are there any other loader projects on going?

AFAIK no one is working on a new loader. I made some improvements on
the MDL loader, but it can't load MSFS 2002 files yet.

>Tengchiang Tsao

Bye bye,
Wolfram.

Re: [Plib-users] ssgLoadBGL

[Steve B. <sjb...@ai...>]

Tengchiang Tsao wrote:
> 
> Hi,
>   This is Tengchiang Tsao. I am modifying scdis
> (http://www.freesc.org) to make ssgLoadBGL.

It's not clear what license SCDIS is under - contributions
to PLIB have to be licensable under LGPL - please check that
this is OK before you do any more!

>   Any one talk to me please. I don't want to give up.
> 
>   Accept me or reject me.

This sounds like a worthwhile project - providing you
can sort out the licensing (and so long as you aren't
violating the DMCA!)
 
>   Are there any other loader projects on going?

People mention that they are working on various loaders
from time to time - but when they give up or lose interest,
they never post to say so - so who knows what's actually
ongoing?
 
>   How are you doing?


----------------------------- Steve Baker -------------------------------
Mail : <sjb...@ai...>   WorkMail: <sj...@li...>
URLs : http://www.sjbaker.org
       http://plib.sf.net http://tuxaqfh.sf.net http://tuxkart.sf.net
       http://prettypoly.sf.net http://freeglut.sf.net
       http://toobular.sf.net   http://lodestone.sf.net

[Plib-users] ssgLoadBGL

[Tengchiang T. <ten...@ya...>]

Hi,
  This is Tengchiang Tsao. I am modifying scdis
(http://www.freesc.org) to make ssgLoadBGL.

  Although my modified version of ssgLoadMDL
successfully loaded a couple of BGL scenery files, 90%
of the other scenery files in the freeware community
still get nothing out of my ssgLoadMDL.

  I hope my way to do ssgLoadBGL (90% of its code is
scdis' code ) can be accepted in plib, but I suspect
ssgLoadBGL.cxx will be more than 8000 lines. And it
will be a lot of work to translate a decompiler (scdis
currently is a decompiler) to a loader.

  A decompiler translates binary data to semi-human
language but I still need to build the stake algorithm
to build ssg's graph branches.

  However, if I don't utilize scdis, it will be even
more work for me. I am really sick and tired of
analizing binary files. I reject to do ssgLoadBGL if I
need to use KDE's binary file viewer (or any other
binary file viewer) ever again!

  Any one talk to me please. I don't want to give up.

  Accept me or reject me.

  Are there any other loader projects on going?

  How are you doing?

Tengchiang Tsao

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Re: [Plib-users] bug in fnt?

[Steve B. <sjb...@ai...>]

Albin Holmgren wrote:
> 
> in void fntTexFont::getBBox(...) (fnt.cxx)
> 
> the following code appers:
> 
>      if ( *s == '\n' )
>      {
>        r = h_pos = 0.0f ;
>        v_pos -= 1.333f ;
>        s++ ;
>        continue ;
>      }
> 
> i *think* that it should read
> 
>      if ( *s == '\n' )
>      {
>        h_pos = 0.0f ; // <- do not reset r
>        v_pos -= 1.333f ;
>        s++ ;
>        continue ;
>      }
> 
> I'm getting correct results after this manipulation (otherwise the width
> returned is that of the last line).

Oooh!  That looks like a good catch.  I think this explains some problems
I had when writing the file selector box.

I've committed the change into CVS.

*MANY* thanks for tracking this nasty little problem down!

----------------------------- Steve Baker -------------------------------
Mail : <sjb...@ai...>   WorkMail: <sj...@li...>
URLs : http://www.sjbaker.org
       http://plib.sf.net http://tuxaqfh.sf.net http://tuxkart.sf.net
       http://prettypoly.sf.net http://freeglut.sf.net
       http://toobular.sf.net   http://lodestone.sf.net

[Plib-users] RE: [Mingw-users] Ported PLIB.

[Norman V. <nh...@ca...>]

Hilbert writes:
>>
>I have ported partial PLIB to Win32 using MinGW ( www.mingw.org ) 
>compiler. If you are interested in the ported files in 
>./plib/MinGW/libplib*.a in the packeage 3DMathPlotter.tar.gz. Download 
>it from https://sourceforge.net/projects/mathdev/

Cool !!  
FYI  AFAIK
PLib builds OTB with MingW32 inside of a Cygwin bash shell

% ./configure --prefix=$PATH_TO_MINGW32_INSTALATION
% make
% make install

I am interested in any problems you encounterd 
and/or any changes that you made

I am also interested in any special steps that you took
if not those I described above

Of course this will all eventually get added to the PLib
distribution so others may benebfit

Cheers

Norman Vine
PLib development team member

[Plib-users] bug in fnt?

[Albin H. <gat...@ti...>]

in void fntTexFont::getBBox(...) (fnt.cxx)

the following code appers:

     if ( *s == '\n' )
     {
       r = h_pos = 0.0f ;
       v_pos -= 1.333f ;
       s++ ;
       continue ;
     }

i *think* that it should read

     if ( *s == '\n' )
     {
       h_pos = 0.0f ; // <- do not reset r
       v_pos -= 1.333f ;
       s++ ;
       continue ;
     }

I'm getting correct results after this manipulation (otherwise the width 
returned is that of the last line).

Or am I just missing something (I wouldn't be suprised).

---
Albin.

[Plib-users] Ported PLIB

[Hilbert <all...@ne...>]

Dear PLIB users,

I have ported partial PLIB to Win32 using MinGW (www.mingw.org) 
compiler. If you are interested in the ported files in 
./plib/MinGW/libplib*.a in the packeage 3DMathPlotter.tar.gz. Download 
it from https://sourceforge.net/projects/mathdev/
-- 
<cid:par...@ne...>

[Plib-users] Flight gear linker probllem with plib

[Rocchi, G. (P. NP) <Gia...@np...>]

Hi, when compiling Flightgear 0.7.8, the linker complains about ssgVtxTable,
saying that the reference symbol is undefined. Obviously I had previously
installed plib shared objects and the configure script that come with
Flightgear can find plib installed.
What can it be?
thankyou

Gianluca

Re: [Plib-users] Please help

[Steve B. <sjb...@ai...>]

Tengchiang Tsao wrote:

>   I am writing ssgLoadBGL.cxx, I test it on PPE.
> Everything looks fine except my textures got tinted to
> gray. If I try to render the same object in FGFS, they
> got tinted to green.
>   Half year ago, Curtis told me I need to explictly
> set the underlying color, otherwise my textures will
> be biased. But how do I do this?
>   I tried state->setMaterial(GL_DIFFUSE, 1.0f, 1.0f,
> 1.0f, 1.0f) and also tried glClearColor(1.0f, 1.0f,
> 1.0f, 1.0f), but they are not helping.

I have just finished writing a small FAQ about OpenGL lighting,
I think it will help to explain your problem.

   http://www.sjbaker.org/steve/omniv/index.html

 
----------------------------- Steve Baker -------------------------------
Mail : <sjb...@ai...>   WorkMail: <sj...@li...>
URLs : http://www.sjbaker.org
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[Plib-users] Please help

[Tengchiang T. <ten...@ya...>]

Hi gurus,
  I am new to plib. One little question, please help.

  I am writing ssgLoadBGL.cxx, I test it on PPE.
Everything looks fine except my textures got tinted to
gray. If I try to render the same object in FGFS, they
got tinted to green.
  Half year ago, Curtis told me I need to explictly
set the underlying color, otherwise my textures will
be biased. But how do I do this?
  I tried state->setMaterial(GL_DIFFUSE, 1.0f, 1.0f,
1.0f, 1.0f) and also tried glClearColor(1.0f, 1.0f,
1.0f, 1.0f), but they are not helping.

  Thanks a lot.

Tengchiang Tsao

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RE: [Plib-users] 'World' to 'Local' body velocity transform

[McEvoy, N. <nic...@ds...>]

"Steve" wrote:
>So (in a nutshell) you want to transform the world-coordinate velocity into
>'body' coordinates.

Thanks for that (nice summary too) !!!

Yes, I have read 'Matrices can be your Friends' too.  Good stuff !  :-)

So ... your_words-to-code seems to be something like this (just the velocity
conversion part from world-to-body) ...

{...

	sgVec3 HPR, Velocity;
	sgMat4 R1, VM;

	// world velocity
	sgSetVec3(Velocity, 0, 100, 0);

	// testing heading changes
	for (int i = 0; i >= -180; i-=45)
	{
		sgSetVec3(HPR, (float)i, 0, (float)i);

		sgMakeRotMat4(R1, HPR);
		sgInvertMat4(R1);
		sgMakeTransMat4(VM, Velocity);
		sgPreMultMat4(R1, VM);

		// body velocity
		sgCoord vel;
		sgSetCoord(&vel, R1);

		printf("HPR <%0.2f> <%0.2f> <%0.2f>\n", HPR[0], HPR[1],
HPR[2]);
		printf("BodyVel <%0.2f> <%0.2f> <%0.2f>\n", vel.xyz[0],
vel.xyz[1], vel.xyz[2]);
	}

...}

Thanks for your suggestion ... I will add it to my game tonight and see if
it fixes my problem ...

Nick
_________________________________________

Nick McEvoy
WorkMail: mailto:nic...@as...
HomeMail: mailto:ndm...@oz...
HomePage: http://members.ozemail.com.au/~ndmcevoy/
_________________________________________

Re: [Plib-users] 'World' to 'Local' body velocity transform

[Steve B. <sjb...@ai...>]

"McEvoy, Nick" wrote:
> 
> I finally have to admit my knowledge of matrix math is very bad !!!  :-(
> 
> I have been struggling with this 'simple' problem for a few days now ... and
> it is driving me crazy !
> 
> Say, I have a 'Body' travelling with a given 'world' velocity and a HPR. As
> the 'Body' changes HPR I want to know what the velocity is in relation to
> the 'bodies local axis' (by this I mean assume the body is facing +ve Y
> direction, +ve Z up, +ve X right ... local coords not world coords) ... (I
> hope this makes sense).

So (in a nutshell) you want to transform the world-coordinate velocity into
'body' coordinates.

You know (or can easily construct) the matrix that converts 'body' coordinates
into 'world' by creating a matrix from the current hpr.

All you need to do is to 'invert' that matrix which switches it from being
a "body-to-world" matrix into a "world-to-body" matrix which you can apply
to the world velocity to turn it into a body velocity.

> MORE EXPLANATION ... The whole reason why I want to do this is to apply a
> damping force to my 'Body' in (xz) directions normal to its +y heading (at
> some ratio to the velocity in these normal directions) ...

So, once you have the veloity in body coordinates, you can simply multiply
the X/Z coordinates by some number a little less than 1.0 every frame and that
will damp it nicely.
 
> HELP ANY SUGGESTIONS PLEASE (I wish I paid attention in high-school math)

Yes - me too.  Matrix math isn't hard though - did you read this yet?

  http://www.sjbaker.org/steve/omniv/matrices_can_be_your_friends.html


----------------------------- Steve Baker -------------------------------
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[Plib-users] 'World' to 'Local' body velocity transform

[McEvoy, N. <nic...@ds...>]

I finally have to admit my knowledge of matrix math is very bad !!!  :-(

I have been struggling with this 'simple' problem for a few days now ... and
it is driving me crazy !

Say, I have a 'Body' travelling with a given 'world' velocity and a HPR. As
the 'Body' changes HPR I want to know what the velocity is in relation to
the 'bodies local axis' (by this I mean assume the body is facing +ve Y
direction, +ve Z up, +ve X right ... local coords not world coords) ... (I
hope this makes sense).

-----------------------------------
Example with body at some hpr (assume the body is facing +ve Y direction,
+ve Z up, +ve X right)
@=World body velocity (XYZ)
*=Local body velocity (xyz)
-----------------------------------

+Z +Y      +y
|  /      /
| /      *-- +z
|/        \
@----+X    +x

I have written some code to rotate the 'world' velocity by the bodies HPR
... but I think this is giving me incorrect results (maybe its the Eulers
are Evil problem: http://www.sjbaker.org/steve/omniv/eulers_are_evil.html)
... but it is hard to say for sure ... (ODE physics engine is involved too
... and at certain HPR the forces I apply to the 'Body' cause it to
accelerate off the screen) ...

MORE EXPLANATION ... The whole reason why I want to do this is to apply a
damping force to my 'Body' in (xz) directions normal to its +y heading (at
some ratio to the velocity in these normal directions) ...

The reason I have not posted my code is so that I do not confuse the issue
... I'm just interested in how other people might suggest to write the code
(using PLIB routines of course) ...

HELP ANY SUGGESTIONS PLEASE (I wish I paid attention in high-school math)
!!!

Nick
_________________________________________

Nick McEvoy
WorkMail: mailto:nic...@as...
HomeMail: mailto:ndm...@oz...
HomePage: http://members.ozemail.com.au/~ndmcevoy/
_________________________________________