visualpython-users

[Visualpython-users] Does Glowscript have numpy-like performance?

[K.-Michael A. <kmi...@gm...>]

Dear all,

I was wondering if the good old VPython gas simulation that uses numpy 
so efficiently will run as nicely in Glowscript? Does Glowscript offer 
efficient arrays?

Best regards,
Michael

Re: [Visualpython-users] Does Glowscript have numpy-like performance?

[Bruce S. <Bru...@nc...>]

The quick answer to "numpy in GlowScript" is "no". GlowScript
(glowscript.org) is necessarily written in JavaScript, and GlowScript
user programs are necessarily written in JavaScript (or CoffeeScript,
which compiles to JavaScript). JavaScript is slower than C++ but
considerably faster than Python. To my knowledge, there is no
possibility for something like numpy, which runs at the speed of C.

However, here is the stars program in GlowScript, a program which is
very similar to the gas program:

http://www.glowscript.org/#/user/GlowScriptDemos/folder/Examples/program/Stars

(You need to enable WebGL in your browser; see the Help at glowscript.org.)

As you see, it runs adequately fast. However, if you examine the code,
you'll see that David Scherer pulled some unintuitive tricks to get
the speed to be adequate. In fairness, you might say that the use of
numpy in the VPython demo programs stars.py and gas.py is also pretty
unintuitive.

Another speed issue to consider is that because GlowScript uses WebGL,
which requires the use of modern GPU-type graphics cards, many kinds
of graphics can be significantly faster than in VPython, which
currently uses GPUs only optionally, for textures. I've been dreaming
of a VPython+ that would also require the use of a modern graphics
card.

I just released GlowScript 1.0 which includes some major new
capabilities. A particularly interesting example is a pulse running
along a rug:

http://www.glowscript.org/#/user/GlowScriptDemos/folder/Examples/program/Rug

For another capability that goes beyond VPython, here is transparency
done right:

http://www.glowscript.org/#/user/GlowScriptDemos/folder/Examples/program/Transparency

In VPython, transparent objects are sorted by their pos attribute,
with the result that intersecting transparent objects cannot be
displayed correctly. I implemented "depth peeling" in GlowScript which
uses the GPUs to do pixel-level sorting. Here are the details:

http://www.khronos.org/message_boards/viewtopic.php?f=44&t=4905

Bruce Sherwood

On Wed, Jun 6, 2012 at 4:46 PM, K.-Michael Aye <kmi...@gm...> wrote:
> Dear all,
>
> I was wondering if the good old VPython gas simulation that uses numpy
> so efficiently will run as nicely in Glowscript? Does Glowscript offer
> efficient arrays?
>
> Best regards,
> Michael

Re: [Visualpython-users] Does Glowscript have numpy-like performance?

[Bruce S. <Bru...@nc...>]

I should add for completeness that JavaScript does offer typed arrays
such as Float32Array, in which all elements are 32-bit floats. A major
use of these typed arrays is for communication between CPU and GPUs on
the graphics card.

Bruce Sherwood

> On Wed, Jun 6, 2012 at 4:46 PM, K.-Michael Aye <kmi...@gm...> wrote:
>> Dear all,
>>
>> I was wondering if the good old VPython gas simulation that uses numpy
>> so efficiently will run as nicely in Glowscript? Does Glowscript offer
>> efficient arrays?
>>
>> Best regards,
>> Michael

Re: [Visualpython-users] Does Glowscript have numpy-like performance?

[Bruce S. <Bru...@nc...>]

I've now converted the VPython demo program gas.py to GlowScript:

http://www.glowscript.org/#/user/GlowScriptDemos/folder/Examples/program/HardSphereGas

To run the program, you need to have a WebGL-enabled browser and a
modern graphics card. For details, see the Help at glowscript.org.

As for speed, this is what I found:

VPython gas.py with 100 atoms, dt = 1e-5, no graphing: 100 iterations
= 1.1 seconds. This similar Glowsript program with same conditions:
100 iterations = 11.7 seconds. Presumably the big difference is the
Python numpy library, which runs at C speed, and which eliminates some
explicit loops.

Bruce Sherwood

Re: [Visualpython-users] Does Glowscript have numpy-like performance?

[Bruce S. <Bru...@nc...>]

Correction: I made my measurements with Chrome on a 64-bit Windows
machine, unaware that Chrome runs slowly on 64-bit machines because it
is a 32-bit application. Here are improved measurements, copied from
comments in the GlowScript program:

On a 32-bit Windows computer running Chrome: VPython gas.py with 100
atoms, dt = 1e-5, rate(100), no graphing: 100 iterations = 1 second.

The similar Glowsript program with same conditions: 100 iterations =
4.5 seconds.

/With rate(300), VPython is 0.35 s, GlowScript remains 4.5 s.

Presumably the big difference is the Python numpy library, which runs
at C speed, and which eliminates some explicit loops.

Note that on a 64-bit Windows computer Chrome runs this program half
as fast as on a 32-bit computer, because Chrome is a 32-bit
application. On 64-bit Windows Firefox is a 64-bit application and
runs the program twice as fast as Chrome.

Bruce Sherwood

On Thu, Jun 7, 2012 at 10:47 PM, Bruce Sherwood <Bru...@nc...> wrote:
> I've now converted the VPython demo program gas.py to GlowScript:
>
> http://www.glowscript.org/#/user/GlowScriptDemos/folder/Examples/program/HardSphereGas
>
> To run the program, you need to have a WebGL-enabled browser and a
> modern graphics card. For details, see the Help at glowscript.org.
>
> As for speed, this is what I found:
>
> VPython gas.py with 100 atoms, dt = 1e-5, no graphing: 100 iterations
> = 1.1 seconds. This similar Glowsript program with same conditions:
> 100 iterations = 11.7 seconds. Presumably the big difference is the
> Python numpy library, which runs at C speed, and which eliminates some
> explicit loops.
>
> Bruce Sherwood

Re: [Visualpython-users] Does Glowscript have numpy-like performance?

[Bruce S. <Bru...@nc...>]

I was wrong. Firefox on my Windows 7 machine is also a 32-bit
application, but it runs the gas program about twice as fast as
Chrome. I also see the higher speed in Safari on a Macbook Pro of
comparable speed.

Bruce Sherwood

On Fri, Jun 8, 2012 at 3:49 PM, Bruce Sherwood <Bru...@nc...> wrote:
> Correction: I made my measurements with Chrome on a 64-bit Windows
> machine, unaware that Chrome runs slowly on 64-bit machines because it
> is a 32-bit application. Here are improved measurements, copied from
> comments in the GlowScript program:
>
> On a 32-bit Windows computer running Chrome: VPython gas.py with 100
> atoms, dt = 1e-5, rate(100), no graphing: 100 iterations = 1 second.
>
> The similar Glowsript program with same conditions: 100 iterations =
> 4.5 seconds.
>
> /With rate(300), VPython is 0.35 s, GlowScript remains 4.5 s.
>
> Presumably the big difference is the Python numpy library, which runs
> at C speed, and which eliminates some explicit loops.
>
> Note that on a 64-bit Windows computer Chrome runs this program half
> as fast as on a 32-bit computer, because Chrome is a 32-bit
> application. On 64-bit Windows Firefox is a 64-bit application and
> runs the program twice as fast as Chrome.
>
> Bruce Sherwood
>
> On Thu, Jun 7, 2012 at 10:47 PM, Bruce Sherwood <Bru...@nc...> wrote:
>> I've now converted the VPython demo program gas.py to GlowScript:
>>
>> http://www.glowscript.org/#/user/GlowScriptDemos/folder/Examples/program/HardSphereGas
>>
>> To run the program, you need to have a WebGL-enabled browser and a
>> modern graphics card. For details, see the Help at glowscript.org.
>>
>> As for speed, this is what I found:
>>
>> VPython gas.py with 100 atoms, dt = 1e-5, no graphing: 100 iterations
>> = 1.1 seconds. This similar Glowsript program with same conditions:
>> 100 iterations = 11.7 seconds. Presumably the big difference is the
>> Python numpy library, which runs at C speed, and which eliminates some
>> explicit loops.
>>
>> Bruce Sherwood

Re: [Visualpython-users] Does Glowscript have numpy-like performance?

[Bruce S. <Bru...@nc...>]

After more study of GlowScript vs. VPython versions of the VPython
gas.py program:

VPython gas.py with 100 atoms, dt = 1e-5, rate 500, no graphing: 100
iterations = 0.4 seconds.

If gas.py is modified to not use numpy, the time is 3.6 s.

The similar Glowsript program with same conditions: 100 iterations =
3.2 seconds on Firefox.

Oddly, on at least one 64-bit Windows machine, the time is 5.3 seconds
on Chrome.

On a 32-bit Windows laptop, 4.2 seconds on Firefox, 2.5 seconds on
Chrome, the reverse of the ordering on the other Windows machine.

There is a very major difference between Chrome and Firefox. With
Firefox, the animation periodically freezes, probably due to
JavaScript garbage collection. These freeze-ups do not occur with
Chrome or Safari.

-----------------------

You can run this program (if you have a WebGL-enabled browser; see the
Help at glowscript.org) at

http://www.glowscript.org/#/user/GlowScriptDemos/folder/Examples/program/HardSphereGas

A summary statement is that the factor of 10 speed advantage of
VPython over GlowScript comes completely from the parallel C-speed
numpy arrays. Without numpy, the VPython and GlowScript (Python and
JavaScript) execution speeds are about the same. I had mistakenly
thought that JavaScript was much faster than Python, but  that seems
not to be the case.

Bruce Sherwood

Re: [Visualpython-users] Does Glowscript have numpy-like performance?

[Bruce S. <Bru...@nc...>]

The plot thickens. David Scherer rewrote a small piece of the
GlowScript gas example, and the time on both Chrome and Firefox
dropped to 1 second, not so different from the 0.4 second seen with
the numpy version. (The change has to do with disabling vector
overloading in the GlowScript handling of JavaScript.)

Bruce Sherwood

On Sun, Jun 10, 2012 at 9:59 PM, Bruce Sherwood <Bru...@nc...> wrote:
> After more study of GlowScript vs. VPython versions of the VPython
> gas.py program:
>
> VPython gas.py with 100 atoms, dt = 1e-5, rate 500, no graphing: 100
> iterations = 0.4 seconds.
>
> If gas.py is modified to not use numpy, the time is 3.6 s.
>
> The similar Glowsript program with same conditions: 100 iterations =
> 3.2 seconds on Firefox.
>
> Oddly, on at least one 64-bit Windows machine, the time is 5.3 seconds
> on Chrome.
>
> On a 32-bit Windows laptop, 4.2 seconds on Firefox, 2.5 seconds on
> Chrome, the reverse of the ordering on the other Windows machine.
>
> There is a very major difference between Chrome and Firefox. With
> Firefox, the animation periodically freezes, probably due to
> JavaScript garbage collection. These freeze-ups do not occur with
> Chrome or Safari.
>
> -----------------------
>
> You can run this program (if you have a WebGL-enabled browser; see the
> Help at glowscript.org) at
>
> http://www.glowscript.org/#/user/GlowScriptDemos/folder/Examples/program/HardSphereGas
>
> A summary statement is that the factor of 10 speed advantage of
> VPython over GlowScript comes completely from the parallel C-speed
> numpy arrays. Without numpy, the VPython and GlowScript (Python and
> JavaScript) execution speeds are about the same. I had mistakenly
> thought that JavaScript was much faster than Python, but  that seems
> not to be the case.
>
> Bruce Sherwood