[vtk-developers] GLSL shader/shaderprogram etc

[Moreland, Kenneth]

John,

I would like to see your changes before you check them in.  Your email
was not exactly clear, but I am assuming you mean you added code to use
the GL_ARB_vertex_program and GL_ARB_fragment_program extensions.  From
what you described, I think I would like to see some changes before that
code gets back into VTK.  Your description gives me two main
reservations.

First, the vtkShaderProgram was meant to be agnostic to the
implementation of the shader.  It should not matter if the
implementation is Cg, GLSL, or GL_ARB_*_program.  Thus, you shouldn't
need to make any changes to it.  That said, we may have forgotten some
generic functionality that you require, for example a method to check to
see if the current shader is supported by hardware.  Either way, I would
like to see the code before it's checked in.

Second, the intention of the vtkShaderProgram hierarchy is to have a
different vtkShaderProgram subclass for each shader API and method for
specifying shader programs.  Thus, I think a better implementation is to
leave vtkGLSLShaderProgram untouched and instead make a new class
(vtkOpenGLShaderProgram?) that implements a shader using OpenGL 1.1
extensions.  The VTK shader code was designed this way specifically to
prevent "messy" (your word, not mine) code that has to handle multiple
implementations with lots of conditionals.

-Ken

   ****      Kenneth Moreland
    ***      Sandia National Laboratories
***********  
*** *** ***  email: kmorel at sandia.gov
**  ***  **  phone: (505) 844-8919
    ***      fax:   (505) 845-0833


> -----Original Message-----
> From: vtk-developers-bounces+kmorel=sandia.gov at vtk.org 
> [mailto:vtk-developers-bounces+kmorel=sandia.gov at vtk.org] On 
> Behalf Of John Biddiscombe
> Sent: Wednesday, May 03, 2006 5:59 AM
> To: vtk-developers at vtk.org
> Subject: [vtk-developers] GLSL shader/shaderprogram etc
> 
> A while back, I made some changes to my copies of 
> vtkShaderProgram.cxx ,vtkShaderProgram.h ,vtkGLSLShader.cxx 
> ,vtkGLSLShader.h ,vtkGLSLShaderProgram.cxx
> 
> so that they will function without OpenGL2 but instead use Gl 
> Extensions (vertex program, shader program etc etc). I've 
> been sitting on these changes for some time in the hope I'd 
> get time to clean them and create some "proxy" or other 
> delegate type object to make them a bit less messy
> - they are full of if (opengl2supported) then {...} otherwise 
> {...} but the functionality is essentially the same for either case.
> 
> I'm going to check these changes in, because I don't think 
> I'm ever going to find time to do a better job of it.
> 
> It primarily lets on do GLSL stuff on some laptops and 
> desktops that don't have gl2 drivers.
> 
> any objections or comments, please send...
> 
> JB
> 
> 
> 
> -- 
> John Biddiscombe,                            email:biddisco @ cscs.ch
> http://www.cscs.ch/about/BJohn.php
> CSCS, Swiss National Supercomputing Centre  | Tel:  +41 (91) 610.82.07
> Via Cantonale, 6928 Manno, Switzerland      | Fax:  +41 (91) 610.82.82
> 
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