| Re: How to use IDLgrShader? [message #54199 is a reply to message #54195] |
Mon, 28 May 2007 17:01  |
Jim Pendleton
Messages: 13
Registered: July 2001
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Junior Member |
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There are a number of examples of both vertex and fragment (pixel)
shading in IDL64\examples\doc\shaders. Two built-in utility classes,
idlgrshaderbytscl__define.pro and idlgrshaderconvol3__define.pro,
can be found in the \lib subdirectory as well.
The IDL docs do not go into a great deal of detail about how to
write a shader program in GLSL (OpenGL Shader Language). That is
left as an exercise for the reader.
Here are a couple items to be aware of, though.
First, debugging a GLSL script is challenging. There is no
"print" statement in GLSL to help you track your scripts'
progress. There are a number of third-party packages that can
assist you, however, such as RenderMonkey, available from ATI
(ati.amd.com). NVIDIA also offers a debugging utility.
Second, you will notice that IDL provides for a software fallback
mechanism if a graphics card doesn't support the shader extension.
In this mode, OpenGL calls back into an IDL routine to get its
vertex and/or pixel values rather than having the graphics card
execute the operations. (See the documentation for the ::Filter
method.) However, some tests have shown that it is often faster
to simply perform the equivalent operation in IDL code without
resorting to the IDLgrShader and a software fallback if the
graphics card does not support shaders. For example an old-fashioned
call to IDLgrImage->SetProperty, Data = BYTSCL(rawdata) will
generally run faster than the software ::Filter callback, but the
IDL code will often be significantly slower than the hardware
acceleration (depending on the size of the image.)
Third, your graphics performance enhancement will be very dependent
on the type of card you have, your CPU(s), and the type of operation
you are attempting to accelerate. Not all cards are created equal and they
are often optimized for one purpose over another. You may find that
there are thresholds for image sizes below which performing calculations
in IDL rather than on the card will result in improved display speed.
Some useful additional sources of information on shading are
"The OpenGL Shading Language" by Randi J. Rost and the
OpenGL Shading Language specification available at OpenGL.org.
Jim P.
<airy.jiang@gmail.com> wrote in message
news:1180338565.647666.123600@a26g2000pre.googlegroups.com.. .
> IDL 6.4 is available.A new IDLgrShader object provides a way to
> associate a shader program with the existing IDL graphic objects.That
> is seemed like a nice tool to increasing the speed of graphics
> rendering dramatically .But how to use it?anyone got the example
> source code,or the demo to show the effect of it?i'll very appreciate
> that someone can answer this question.
>
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