Data parsimony and WebGL shaders - SFx Discuss

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Message from discussion Data parsimony and WebGL shaders
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Date: Thu, 17 May 2012 10:16:11 -0600
Message-ID: <CAN_LYRmR1VskeFyTor1troAgSNz=EA1tWSU-Fz89ETwXjFP...@mail.gmail.com>
Subject: Re: [sfx: Discuss] Data parsimony and WebGL shaders
From: Owen Densmore <o...@backspaces.net>
To: disc...@sfcomplex.org
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Fascinating!

I looked at the CS code and it made a lot of sense.  What wasn't clear is
the GPU interactions.

So in terms of data sent to the shader, I'm guessing you send just the
vertices to your vertex attribute buffer, so you don't have to store
multiple copies of the same vertex in the GPU.  You then have a pretty
sophisticated binding of these vertices to the image for texture drawing.
 Is that right?  .. or do you have to replicate the vertices to keep the
shaders simple?

Just as a point of interest, where *are* the shaders?  My guess is that
GlowScript has a set of standard shaders and separate program objects for
standard use.

CS/GS certainly are very readable.

   -- Owen

On Thu, May 17, 2012 at 9:33 AM, Bruce Sherwood <bruce.sherw...@gmail.com>wrote:

> I've had a lot of trouble with WebGL shader code working on my Windows
> machine and failing on a Macbook Pro and Ubuntu, all with NVIDIA
> graphics and drivers.
>
> I did a lot of work to ensure that I send to each of the many shaders
> only that data that is actually referenced and used by that particular
> shader, and this change made mouse picking and transparency work again
> on all platforms. Moral of the tale: don't send anything from CPU to
> shaders that the shaders aren't going to use, even though this works
> okay on Windows. It seems to me that the shader compilers in the Mac
> and Ubuntu drivers are wrong, but at least now I know what to do to
> preserve cross-platform compatibility.
>
> In other news, over the last couple of weeks I had intensive
> discussions with David Scherer about the GlowScript API for creating
> your own models out of triangles or quads and dynamically modifying
> them to change the shape of the object. I'm working toward a major
> release, 1.0. Some time ago I posted an example of a pulse moving
> along a rug, which has been rewritten with the new API:
>
> http://www.glowscript.org/#/user/Bruce_Sherwood/folder/Pub/program/Rug
>
> To take the rug as a specific example, I create a set of vertices
> covering the rug in a rectangular pattern. I then create quad objects
> for each group of 4 vertices, with vertices internal to the rug shared
> among 4 adjacent quads. The animation of the pulse running along the
> rug is then done simply by modifying the vertices, with no need to
> think about the quads that make the display. Take a look at the
> CoffeeScript source code for the rug; it's now quite simple.
>
> Bruce
>
> --
> You received this message because you are subscribed to the Santa Fe
> Complex "discuss" group.
> To post to this group, send email to disc...@sfcomplex.org
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<font color=3D"#000000"><font><font face=3D"verdana,sans-serif">Fascinating=
!</font></font></font><div><font color=3D"#000000"><font><font face=3D"verd=
ana,sans-serif"><br></font></font></font></div><div><font color=3D"#000000"=
><font><font face=3D"verdana,sans-serif">I looked at the CS code and it mad=
e a lot of sense. =A0What wasn&#39;t clear is the GPU interactions.</font><=
/font></font></div>
<div><font color=3D"#000000"><font><font face=3D"verdana,sans-serif"><br></=
font></font></font></div><div><font color=3D"#000000"><font><font face=3D"v=
erdana,sans-serif">So in terms of data sent to the shader, I&#39;m guessing=
 you send just the vertices to your vertex attribute buffer, so you don&#39=
;t have to store multiple copies of the same vertex in the GPU. =A0You then=
 have a pretty sophisticated binding of these vertices to the image for tex=
ture drawing. =A0Is that right? =A0.. or do you have to replicate the verti=
ces to keep the shaders simple?</font></font></font></div>
<div><font color=3D"#000000"><font><font face=3D"verdana,sans-serif"><br></=
font></font></font></div><div><font color=3D"#000000"><font><font face=3D"v=
erdana,sans-serif">Just as a point of interest, where *are* the shaders? =
=A0My guess is that GlowScript has a set of standard shaders and separate p=
rogram objects for standard use.</font></font></font></div>
<div><font color=3D"#000000"><font><font face=3D"verdana,sans-serif"><br></=
font></font></font></div><div><font color=3D"#000000"><font><font face=3D"v=
erdana,sans-serif">CS/GS certainly are very readable.</font></font></font><=
/div>
<div><font color=3D"#000000"><font><font face=3D"verdana,sans-serif"><br></=
font></font></font></div><div><font color=3D"#000000"><font><font face=3D"v=
erdana,sans-serif">=A0 =A0-- Owen=A0<br></font></font></font><br><div class=
=3D"gmail_quote">
On Thu, May 17, 2012 at 9:33 AM, Bruce Sherwood <span dir=3D"ltr">&lt;<a hr=
ef=3D"mailto:bruce.sherw...@gmail.com" target=3D"_blank">bruce.sherwood@gma=
il.com</a>&gt;</span> wrote:<br><blockquote class=3D"gmail_quote" style=3D"=
margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
I&#39;ve had a lot of trouble with WebGL shader code working on my Windows<=
br>
machine and failing on a Macbook Pro and Ubuntu, all with NVIDIA<br>
graphics and drivers.<br>
<br>
I did a lot of work to ensure that I send to each of the many shaders<br>
only that data that is actually referenced and used by that particular<br>
shader, and this change made mouse picking and transparency work again<br>
on all platforms. Moral of the tale: don&#39;t send anything from CPU to<br=
>
shaders that the shaders aren&#39;t going to use, even though this works<br=
>
okay on Windows. It seems to me that the shader compilers in the Mac<br>
and Ubuntu drivers are wrong, but at least now I know what to do to<br>
preserve cross-platform compatibility.<br>
<br>
In other news, over the last couple of weeks I had intensive<br>
discussions with David Scherer about the GlowScript API for creating<br>
your own models out of triangles or quads and dynamically modifying<br>
them to change the shape of the object. I&#39;m working toward a major<br>
release, 1.0. Some time ago I posted an example of a pulse moving<br>
along a rug, which has been rewritten with the new API:<br>
<br>
<a href=3D"http://www.glowscript.org/#/user/Bruce_Sherwood/folder/Pub/progr=
am/Rug" target=3D"_blank">http://www.glowscript.org/#/user/Bruce_Sherwood/f=
older/Pub/program/Rug</a><br>
<br>
To take the rug as a specific example, I create a set of vertices<br>
covering the rug in a rectangular pattern. I then create quad objects<br>
for each group of 4 vertices, with vertices internal to the rug shared<br>
among 4 adjacent quads. The animation of the pulse running along the<br>
rug is then done simply by modifying the vertices, with no need to<br>
think about the quads that make the display. Take a look at the<br>
CoffeeScript source code for the rug; it&#39;s now quite simple.<br>
<span class=3D"HOEnZb"><font color=3D"#888888"><br>
Bruce<br>
<br>
--<br>
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</font></span></blockquote></div><br></div>

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