[Chimera-users] new Chimera snapshot release

[Greg Couch]

On Tue, 19 Oct 2004, Charles Moad wrote:

> The release notes include: initial OpenGL Shading Language API support.
>
> Do you have any documentation on how you expose this functionality, or
> could you offer a brief explanation on how you see it being integrated?

So everyone understands the power of the OpenGL Shading Language, OGLSL, 
the idea of using shaders is to provide interactive stylized images. 
Especially black and white images for publication, but possibly for other 
effects too.  The attached image has a molecular surface covered with 
bricks using OGLSL, which has dubious scientific value, but as a proof of 
concept shows the power of shaders.

The initial OGLSL support is exposed via chimera python scripts.  Enclosed 
below is testshader.py which as used to produce the brick surface.

Shaders fit in to the existing chimera internal dichotomy of ColorGroups 
amd Colors.  Color groups are textures, materials, or shaders and colors 
are per vertex attributes for a particular color group.  So for textures 
those attributes are texture coordinates, for materials the attributes are 
RGBA (the diffuse component), and for shaders the attributes are the OGLSL 
varying data.

A shader is expected to be packaged as a directory with an XML file, 
shader.xml, giving meta-information about the shader and links to 
individual vertex and fragment shader files.  Enclosed below is an example 
of the current version of the XML format.  It may change as I learn more 
about OGLSL and XML.  The current "shader color" is a place holder and 
does not set any per-vertex attributes so the shader program needs to 
figure out what to do from standard OpenGL pipeline data.  Luckily, many 
of the book examples fall into this category, like the brick shader used 
in the attached image.

Since shader programs are tightly integrated into applications, I will 
have to document what OpenGL state a shader may expect and should use. For 
example, the brick shader, that I tested with, takes a LightPosition 
parameter rather than use the current set of OpenGL lights.  That makes 
for a simplier example, but effectively disables chimera's lighting 
interface.

I would welcome alpha testers, so please speak up if you wish to 
participate in developing this feature.  The more programming skill and 
OGLSL knowledge, the better initially as the work will be to write 
appropriate shaders and possibly modify chimera to provide computed data 
to shaders.  And the user interface will need work too. :-)

 	Hope this helps,

 	Greg Couch
 	UCSF Computer Graphics Lab
 	gregc at cgl.ucsf.edu

-------------
testshader.py
-------------
import chimera
import Midas
Midas.open('1gcn')
m = chimera.openModels.list()[0]
Midas.surface('#', 'main')
s = chimera.Shader_lookup('brick')
sc = chimera.ShaderColor(s)
m.surfaceColor = sc

-----------------------------------
~/.chimera/shaders/brick/shader.xml
-----------------------------------
<?xml version="1.0" ?>
<vertex_shader filename="brick.vert"/>
<fragment_shader filename="brick.frag"/>
<uniform name="BrickColor" type="vec3" metatype="color">
 	1.0 0.3 0.2
</uniform>
<uniform name="MortarColor" type="vec3" metatype="color">
 	0.85 0.86 0.84
</uniform>
<uniform name="BrickSize" type="vec2">
         0.30 0.15
         <min> 0.0 0.0 </min>
         <max> 1.0 1.0 </max>
</uniform>
<uniform name="BrickPct" type="vec2">
         0.90 0.85
         <min> 0.0 0.0 </min>
         <max> 1.0 1.0 </max>
</uniform>
<uniform name="LightPosition" type="vec3">
         0.0 0.0 4.0
         <min> -10.0 -10.0 -10.0 </min>
         <max> 10.0 10.0 10.0 </max>
</uniform>
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