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Don't know about your exact time schedule, but knocking up an RT-Shader
which does what you want should take an experienced programmer one or
two days. The OGL Shaders have the advantage that you can actually work
on top of them, while the DX ones open up in a seperate viewport which
does not show selections, wireframes, etc...
-André
Fred Jacob wrote:
Thx Andy for the thorough reply.
I need this for a game we're working on that does the same blending at runtime, so there's no point in baking maps or rendering anything at all.
"Writing" a shader is what I did by using ShaderFX, which is more like connecting nodes and exporting the resulting shader code
as an *.fx file. However, loading the fx file in XSI "works" (that is: it does not crash) by loading it through the DXFX2 DX9 shading node, but does not render anything.
See attached fx file for reference if you dare.
What would be the benefit of using Cg over DX?
Are there graphical editors that can output Cg code? I was hoping for Mental Mill but that's not released yet as it seems.
The thing is I really don't want to get into shader programming right now as our time schedule is really tight.
Thanks again for your input,
Stefan
-------- Original-Nachricht --------
Datum: Sat, 05 May 2007 16:30:40 +0200
Von: Andy Jones <andy(at)thefront.com>
An: XSI(at)Softimage.COM
Betreff: Re: How to blend 2 textures based on vertex alpha values in realtime viewports
Hey Stefan,
I have four approaches I can propose. The first would involve coding a
custom cg shader yourself, or having someone else do it. This all
happens in the interface, so it's not as bad as having to write a shader
in C or something (though generally, I'd say writing MR shaders in C can
be easier than writing RT shaders in cg, depending on what you're
doing). Having to write some code to do something like what you're
describing is ultimately not such a bad thing, as once you know how to
code these things, you can pretty much do anything you think of within
the limits of the hardware. This is the solution I recommend. To
access the vertex colors in XSI with a cg shader, you use the COLOR0
semantic. This is also handy in general, because even if you don't have
a vertex color map, it reads the diffuse color. At least, that's how I
remember it working... My experience doing this in XSI has mostly been
with the CGProgram node. But if I were starting all over, I'd probably
try to do everything with the .fx plugin. You can definitely do what
you're trying to do with custom cg programs.
The other possible solution I know for doing texture blending, which I'm
not even sure works, is to use a 2-pass shader with the standard OpenGL
nodes. Basically, this just means you have to OpenGL Draw nodes in the
shader. Each draws something to the screen. So, in this case, each one
would draw one of the textures and you'd have to attenuate them somehow,
via the blending modes in the draw node. But I'm not actually sure if
you can read the vertex colors from any of the OpenGL nodes, so that
might not actually work.
The third option is to set up a mental ray shader and just rendermap
it. Whether that's useful depends on what you're doing, but a lot of
times it's just way easier and faster to do complicated stuff like this
with MR. In a few cases, I've foolishly squandered hours trying to do
things in realtime, when sometimes just doing it in MR and dealing with
non real-time viewport updates just isn't so bad.
The fourth option would be to use the FX tree to do the texture blending
for you, onto a single clip. Although, there might be somedifficulty
with the vertex colors. I suppose you could rendermap those... But it
all depends on what your workflow is.
Hope this helps.
-Andy
Fred Jacob wrote:
Good morning list!
I've been trying to set up a shading network that would show 2 textures
blended over each other on a per vertex alpha value basis.
I want to paint the vertex alpha values using the paint tool, but I don't
want to render region after every paint stroke I do to see the effect so I
need this to be displayed in realtime.
So far I was not very successful in setting up a realtime shader that
would
do that. I tried with the fixed function DX, Cg and OpenGl shading nodes
XSI provides out of the box to no avail, and I also tried using an fx file
I created with the ShaderFX plugin for 3dsMax (which seems to fail to
render in XSI propery because the shader queries the vertex colors in a
Max-compatible way, which seems to be different in XSI).
Any hint towards an alternative approach, a link to a working OpenGL
shader (or whatever allows me to work in the viewports, 'cause in DirectX
display mode no tools seem to display
correctly, including manipulators of the SRT tools and the paint tools,
which renders DX display a bit useless in the first place) is highly
appreciated.
Also, I was wondering if there are any plans to integrate Mental Mill
into XSI at some point.
Thanks a lot,
Stefan
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