visualpython-users

[Visualpython-users] Images in VPython

[Joel K. <jj...@ya...>]

First: a member of the Python Edu-Sig group sent me a
bug fix for my image-to-object script. The way I
originally wrote it, bitmaps with less than 24 bits
per pixel may not work. If you insert this line . . .

Picture = Picture.convert("RGB")

. . . after the "Image.open" command, your bitmap data
will be in the right format to be handled properly by
both PIL and VPython.

Second: Jonathan's summary of the texture-mapping
prospects was educational, even though much of it was
beyond my level of expertise. One point that did come
through clearly was the need for powerful hardware to
handle (let alone animate) any significant number of
detailed texture-matched objects. I think that this
would be a good justification for a VPython-oriented
cluster experiment. Does anybody have the time and the
interest to join me in putting together some kind of
grant proposal for a Beowulf project? I'm open to any
relevant suggestions. . . .

Joel



		
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Re: [Visualpython-users] Images in VPython

[Jonathan B. <jbr...@ea...>]

On Wed, 2004-09-08 at 16:27, Joel Kahn wrote:
> First: a member of the Python Edu-Sig group sent me a
> bug fix for my image-to-object script. The way I
> originally wrote it, bitmaps with less than 24 bits
> per pixel may not work. If you insert this line . . .
> 
> Picture = Picture.convert("RGB")
> 
> . . . after the "Image.open" command, your bitmap data
> will be in the right format to be handled properly by
> both PIL and VPython.
> 
> Second: Jonathan's summary of the texture-mapping
> prospects was educational, even though much of it was
> beyond my level of expertise. One point that did come
> through clearly was the need for powerful hardware to
> handle (let alone animate) any significant number of
> detailed texture-matched objects. I think that this
> would be a good justification for a VPython-oriented
> cluster experiment. Does anybody have the time and the
> interest to join me in putting together some kind of
> grant proposal for a Beowulf project? I'm open to any
> relevant suggestions. . . .
> 
> Joel


Cluster?  No, I think that would be a bad idea for VPython.  Any recent
video card will be able to handle pretty much anything you can throw at
it from VPython.  A scene with several translucent and textured objects,
some using a source image of 1024x2048 pixels, can be rendered in only a
few ms on common PC hardware.  You really can't notice that it takes any
time at all, and the UI remains buttery-smooth.

Speed is not the problem.  Picking the right parts of a complex
environment (or completely reformulating the appearance of what you are
doing) to expose to client programs in Python is the hard part, and that
is what I would appreciate some feedback on.

-Jonathan

Re: [Visualpython-users] Images in VPython

[Jon S. <js...@so...>]

>
> Speed is not the problem.  Picking the right parts of a complex
> environment (or completely reformulating the appearance of what you are
> doing) to expose to client programs in Python is the hard part, and 
> that
> is what I would appreciate some feedback on.
>

I'm excited to hear about these developments, but got lost in the trees 
of your description of the issues.

On the off chance that you too are lost in the trees of coding, I want 
to make sure that the basic vpython aesthetic is not being overlooked.  
Pixels, for example, are several levels more molecular than I would 
likely want to work.

I'd want to be able assign texture and transparency to an *object*'s 
surface.  The positioning of the texture on the object might be 
controlled by rotating the texture around the center of the object.  
The texture would automagically slide around on the surface of the 
object.

Since transparency is now an option (and this is very good news!)  The 
surfaces of objects might also have thicknesses (with defaults of 
course).  And the interiors might have a density/opacity parameter as 
well.

The default condition I think should be thickness=.00001 (just enough 
to put a texture on) and opacity=1.

And then vpython would do all of the per-pixel calculation (and 
shadowing and light scattering) under the hood, as is its "true 
nature".

I hope this is helpful  or suggestive.

Regards,


=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Jon Schull, Ph.D.
Associate Professor
Information Technology
Rochester Institute of Technology
102 Lomb Memorial Drive
Rochester, New York 14623
sc...@di... 585-738-6696

Re: [Visualpython-users] Images in VPython

[Jonathan B. <jbr...@ea...>]

On Thu, 2004-09-09 at 08:53, Jon Schull wrote:
> >
> > Speed is not the problem.  Picking the right parts of a complex
> > environment (or completely reformulating the appearance of what you are
> > doing) to expose to client programs in Python is the hard part, and 
> > that
> > is what I would appreciate some feedback on.
> >
> 
> I'm excited to hear about these developments, but got lost in the trees 
> of your description of the issues.
> 
> On the off chance that you too are lost in the trees of coding, I want 
> to make sure that the basic vpython aesthetic is not being overlooked.  
> Pixels, for example, are several levels more molecular than I would 
> likely want to work.
> 
> I'd want to be able assign texture and transparency to an *object*'s 
> surface.  The positioning of the texture on the object might be 
> controlled by rotating the texture around the center of the object.  
> The texture would automagically slide around on the surface of the 
> object.

That is the idea.  There are two means of automatic texture-coordinate
generation (the texture coordinates specify how to wrap the texture to
the object).  The first is a kind of planar projection, where you
specify the position of the texture in world space, and it is linearly
projected onto the surface of the body.  The second is similar to that,
except that the position of the texture is specified in screen space,
meaning that it is projected from somewhere relative to your monitor.

For those bodies where an obvious algorithm exists for mapping the
texture, we can provide a default mapping.  The box object simply maps
the texture in its entirety to each plane.  The sphere (and by
extension, the ellipse) wraps the texture around itself as though the
texture were laid out like 
http://earthobservatory.nasa.gov/Newsroom/BlueMarble/Images/land_ocean_ice_cloud_2048.jpg

I haven't decided on default mappings for the other objects.  The
cylinder could support three separate textures (the side and each end). 
The cone can do something similar, and the ring has a reasonable one
too.  I can't think of a sane default for the arrow object, yet.

> Since transparency is now an option (and this is very good news!)  The 
> surfaces of objects might also have thicknesses (with defaults of 
> course).  And the interiors might have a density/opacity parameter as 
> well.

Well, that is the catch with transparency.  You can only really set
transparency for an individual zero-thickness planar triangle in
OpenGL.  So, on the outside, we expose a model where the entire body is
controlled by a common opacity value, tentatively named 'alpha', but it
should probably be named 'opacity'.

> The default condition I think should be thickness=.00001 (just enough 
> to put a texture on) and opacity=1.
> 
> And then vpython would do all of the per-pixel calculation (and 
> shadowing and light scattering) under the hood, as is its "true 
> nature".

The only thing that you would have to do per-pixel is generate the
texture itself, and only then if you are not loading the image from a
file.

Shadowing and light scattering are things that OpenGL does not support,
directly.  They can be emulated indirectly, but not to the extent that
you would expect from say, a raytracing package.  

The code for the translucent boxes demo looks like this:

from visual import *
# Verify the dimensions of the bodies, with a known unit-length
# object.
yardstick = arrow()
box( pos=(2, 0, 0), alpha=0.4)
box( pos=(-2, 0, 0))
# file_texture objects inherit from 'texture', which most Visual objects
# can use
panel = file_texture( "crate.bmp")
box( pos=(0, 2, 0), texture=panel)
box( pos=(0, -2, 0), texture=panel, color=(1, 1, 1, 0.5))
sphere( pos=(0, -2, 0), radius=0.4)

Re: [Visualpython-users] Images in VPython

[Jonathan B. <jbr...@ea...>]

On Thu, 2004-09-09 at 10:20, Jonathan Brandmeyer wrote:
>   You can only really set
> transparency for an individual zero-thickness planar triangle in
> OpenGL.  

That is not strictly true.  You can also specify it for a point, whose
size is measured in pixels.  Flames and fog clouds are done this way, in
games, and the tech to do it is commonly called a 'particle engine', if
you want to google for more info.

Visual doesn't have a 'points' object yet, but a team in Australia is
working on one.  I don't know if they intend to imbue it with particle
engine functionality, but I think it is meant to be more like the
'curve' object.

-Jonathan