Subject:
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Re: Several replies to CLIPPING / WINDING
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Newsgroups:
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lugnet.cad.dev
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Date:
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Mon, 18 Oct 1999 16:26:45 GMT
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Reply-To:
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rui.martins@link*IHateSpam*.pt
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Viewed:
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387 times
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On Mon, 18 Oct 1999, Leonardo Zide wrote:
> Rui Martins wrote:
> >
> > Well, the ideia is to minimize the state change, but if you have to make
> > some, that is not so drastic. On some hardware, some state/option
> > changes, force a flush in the hardware buffers, which breaks up the
> > pipeline & eventually hurts performance, but this is not the case.
>
> I understand that you would be allowed to have as many "0 CCW"/"0 CW"
> lines as you want. This will hurt performance and of course, it would be
> better if you could use only 1 call per part.
In fact you can, use as many as you like, but that it's not the goal.
if you read my previous mail, following this one I'am replying, you got
the ideia that no WINDING meta command is the ideia, if the .DAT is well
optimized.
If someone want's to, he can make a very heavy .DAT file, by doing
to many state changes, or even do state changes with no usefullness,
just to bog down the drawer program, we can' fight a bad behaved
builder. But in the other way, no one would see is files, no one likes
to wait too much.
>
> > One nasty case is to mix 2D & 3D rendering, every time you change from 2D
> > to 3D rendering, in every hardware available, it forces a flush, and
> > performance will probably drop significantly.
>
> You don't need to do that with LDraw files, except for writing any
> text on the screen. :)
I new that, just giving a tip! ;)
> > I think that what you are referring is "display lists", which in fact
> > are controlled by your program, which you are responsible to optimize.
> > So this is not very relevant, even because an optimized part will be
> > loaded an kept in a display list for further reference, an also because
> > an optimized .DAT file will have an unique meta command "0 CLIPPING ON"
>
> I wasn't talking about display lists, and I don't think that the
> discussion is going to lead to a single "0 CLIPPING ON" meta command.
See my previous mail!
> The OpenGL drivers are not forced to do any optimizations in the display
> lists, if they want they can just copy the same commands when you call
> the list.
yes they are not forced to, but if they want to compete in the marked,
they have to strive for every bit of performance that they can squeeze
of their specific hardware.
So, we should always hope for the best, not the worst. because the worst
case has no solution on our side.
> > R> Another problem is that you have to send the elements in a slower way
> > R> to be able to change the culling parameters. If you don't believe me
> >
> > Never heard that one! ;)
> > Could someone enlighten me ?
>
> I meant that you would have to use a glEnd(), call glFrontFace() and
> then glBegin() again, which is much slower than having everything drawn
> with a single call to glDrawElements().
Thank you, for reminding me that!
but I think that you are assuming that only tris or only quads, not
both, which is not the case. Because if you have both, then you would be
forced to do a glBegin/glEnd pair anyway, (but the glFrontFace could not
be needed if you didn't change the state)
---------------------------------------------------------------------
NOTE: this reminds me:
you should always pair the tris and the quads together so that
the glBegin/glEnd pairs are minimized.
---------------------------------------------------------------------
> > This depends on what changes you change.
> > But the use of vertex arrays is the wait to go, because it reduces the
> > amount of floating point math, because usually an object shares several
> > vertexs between several polygons.
>
> Not exactly, you have to lock the arrays to have the vertexes
> transformed only once and you can't change any states (not even the
> colors) while you have the arrays locked. Or if you are using a display
> list and if who wrote the driver was smart enough then the vertexes will
> be transformed once (but you can't assume that).
Let's hope for the best!
> To use a vertex array you also need to have all vertexes indexed,
> which is not the case of the DAT files and one of the reasons why I have
> my own file format.
To Drawer program, can do this job of indexing.
But I know that it is difficult, when some programs put 2,0001 or
1,99998 instead of 2, for example, this could be a goal for improvement
in ldraw compatible editors.
( VI/NOTEPAD are the best for the JOB! 8)
-------------
Rui Martins
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Message has 2 Replies:
 | | Re: Several replies to CLIPPING / WINDING
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| Rui Martins wrote in message ... (...) Wait a minute, you were not going to actually send winding state changes to the graphics engine? Simply keep track of the state yourself and send either vertices 1,2,3 or 3,2,1. The part author can use as many (...) (25 years ago, 19-Oct-99, to lugnet.cad.dev)
| | | Re: Several replies to CLIPPING / WINDING
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| (...) We both want the same thing, now we need to make everybody agree with us :) (...) I sort first by color and then by line type. I have everything pre-processed and I don't use glBegin()/glEnd() to render. (...) From my personal experience, (...) (25 years ago, 19-Oct-99, to lugnet.cad.dev)
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Message is in Reply To:
| | Re: Several replies to CLIPPING / WINDING
|
| (...) I understand that you would be allowed to have as many "0 CCW"/"0 CW" lines as you want. This will hurt performance and of course, it would be better if you could use only 1 call per part. (...) You don't need to do that with LDraw files, (...) (25 years ago, 18-Oct-99, to lugnet.cad.dev)
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