Subject:
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Re: 3D Transformations Architecture Question
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Newsgroups:
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lugnet.cad
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Date:
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Fri, 13 Jul 2007 00:31:32 GMT
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Viewed:
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1936 times
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Basically you keep 1 copy of the object with its vertices in their
original position (local or model space).
You take the local to world, world to view, view to projection and
projection to viewport matrices and multiply them to get a single
matrix, then you multiply each vertex by that matrix when rasterizing
the triangles.
Matrix names often change depending on the API that you use (OGL
vs D3D) and sometimes the projection matrix has the viewport in it,
but the idea is pretty much the same.
On Jul 12, 2007, at 11:00 PM, Jeff Boen wrote:
> Feedback from the guys who built the viewers (LDGlite, LDView, etc)
> would be
> really great on this.
>
> I have a project, not Lego, but similar and I'm writing some
> software for 3D
> viewing and manipulation of items. The LDraw architecture is a good
> match so I'm
> adapting some of the concepts we use.
>
> I have a question about how you guys attack all the necessary
> transformations
> needed for viewing. This isn't a "How do you do 3D?" question, I've
> got all the
> data structures, transformation matrices and drawing routines
> implemented. This
> is more about how much you process on the fly and how much you
> store. Before I
> go down the road of implementing my transformation/drawing engine I
> want to make
> sure I'm not heading down a path that will only waste time.
>
> I have my 3D vertex data, modeled in 3DSMax and imported into
> Visual Studio via
> some routines I wrote. I store these vertices in objects which also
> have
> Translation, Scaling and Rotation vectors (each 3D).
>
> Now, each time I need to move, scale or rotate one of these
> objects, I could
> just apply formulas directly to the vertex data, but that doesn't
> seem very
> elegant and modifies my raw object data.
>
> I could edit the stored Trans, Scale and Rotation vectors with new
> values,
> generate a transformation matrix (Trans, Scale, Rot) based on these
> values, then
> apply that to vertices, but again, I'm modifying my original object
> directly.
>
> I could apply said transformation matrix to a clone of the vertex
> data which
> would be created, drawn, then destroyed once drawing was complete,
> but this
> means I'm going through lots of math for every change of an object.
> And if I'm
> redrawing every object on the screen due to a change in one that
> means lots of
> transformation math to obtain data that didn't actually need updating.
>
> I could at least store each object's transformation matrix and only
> recalc it
> when the object's Trans, Scale, or Rot values change, but this
> still means I
> have to do all the actual transformation math applied to each
> vertex for every
> change. I believe that this stored transformation matrix is how
> much of the
> LDraw software functions, thus making up the 9 of the 12 numbers we
> all know and
> love on every line of a .DAT/.LDR file. But I might be wrong.
>
> Or, I could store 2 sets of vertex data. The raw, original object
> data, and the
> transformed vertices, which I would only update when the Trans,
> Scale, or Rot
> values change. This would maintain my original vertex data and also
> allow me to
> have quick access to current draw data, but at the expense of
> essentially
> doubling the amount of vertex data I keep in memory.
>
> So the ultimate question is, for the guys who wrote LDraw viewers/
> editors, do
> you do all the transformation math for every object all the time,
> or do you
> store much of the data and only update it when necessary?
>
> I know I can do this all in OpenGL or D3D and probably not have to
> worry about
> most of it, but I want to do it myself for real first to completely
> understand
> it, then I'll port it.
>
> Any advice? Or am I completely off-base with all this analysis?
>
> TIA
> Jeff
> onyx(at)brickgun.com
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Message is in Reply To:
 | | 3D Transformations Architecture Question
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| Feedback from the guys who built the viewers (LDGlite, LDView, etc) would be really great on this. I have a project, not Lego, but similar and I'm writing some software for 3D viewing and manipulation of items. The LDraw architecture is a good match (...) (17 years ago, 12-Jul-07, to lugnet.cad)
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