[osg-users] OpenGL ES 2.0 and LIGHTING

[Grigoriy Mylnikov]

Hi,

Is this issue solved in OSG somehow? I need to use some basic lighting on Android (GLESv3). It should use parameters from osg::Light. Are there any ready-made solutions?
if not, where can I get some shaders/shader generator to start with? I'm new in shaders.

Thank you!

Cheers,
Grigoriy

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[Chris Hanson]

I think the osgUtil/ShaderGen code might be GLES2 compatible now. Try
running it on your model, and dump the shader that it creates to see if
it's creating Uniforms for lighting or not.

It might or might not be using the osg::Light as a basis. Do you HAVE to
use osg::Light or could you get by with some light Uniforms?

Describe to us your lighting requirements better and maybe we can suggest
solutions.

Post by Grigoriy Mylnikov
Hi,
Is this issue solved in OSG somehow? I need to use some basic lighting on
Android (GLESv3). It should use parameters from osg::Light. Are there any
ready-made solutions?
if not, where can I get some shaders/shader generator to start with? I'm new in shaders.
Thank you!
Cheers,
Grigoriy
------------------
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[Grigoriy Mylnikov]

Sorry for delayed reply.

My goal is to open and display .osgt files on android the same way they can be opened on desktop. This includes using several lights inside a model, both directional and point lights.

I have some progress with writing shaders, but I have troubles with understanding OSG states. I've updated osg::Light apply() code to pass light position (relative to camera) as uniform:


Code:
void LightShader::apply(osg::State& state) const
{
#ifdef OSG_GL_FIXED_FUNCTION_AVAILABLE
... // Original code
#else
...
osg::Vec4 relPos = state.getModelViewMatrix() * _position;
lightPosUniform.get()->set(relPos);
...
#endif
}




But it seems that state.getModelViewMatrix() does not gives me valid view matrix.

If I could get light position (relative to camera), I can use it in shaders like this:


Code:
vec3 APos = vec3(gl_ModelViewMatrix * gl_Vertex);
...
vec3 fromPointToLight = lightPos.xyz - APos;




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[Werner Modenbach]

Hi Grigoriy,

why don't you do the multiply in the shader like you do with gl_vertex?

- Werner -

Post by Grigoriy Mylnikov
Sorry for delayed reply.
My goal is to open and display .osgt files on android the same way they can be opened on desktop. This includes using several lights inside a model, both directional and point lights.
void LightShader::apply(osg::State& state) const
{
#ifdef OSG_GL_FIXED_FUNCTION_AVAILABLE
... // Original code
#else
...
osg::Vec4 relPos = state.getModelViewMatrix() * _position;
lightPosUniform.get()->set(relPos);
...
#endif
}
But it seems that state.getModelViewMatrix() does not gives me valid view matrix.
vec3 APos = vec3(gl_ModelViewMatrix * gl_Vertex);
...
vec3 fromPointToLight = lightPos.xyz - APos;
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[Grigoriy Mylnikov]

After some trial and errors, I managed to do it in shader. But this means one redundant matrix multiplication per each vertex. Isn't it more effective to compute it once per frame on cpu side?

What's the purpose of state.getModelViewMatrix()? I expected to get a camera*model matrix there. Or it is not yet defined at the moment lights are applied?

------------------
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[Grigoriy Mylnikov]

I tried to use osgUtil/ShaderGen. As far as I understand, it does not supports GLES2/3: it references gl_LightSource, gl_FrontLightProduct etc. in shader code, and I could not find such uniforms created. Also, it assumes only one light source.
Maybe there is some more advanced version of ShaderGen? I have seen somebody mentioned it somewhere on this forum.
Does anyone work on supporting GLES in OSG? I could try to help with this, if somebody will point me in right direction

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[Grigoriy Mylnikov]

At the moment, I implemented ShaderLight class that extends osg::Light and allows to use several point lights with per-pixel lighting (using my shaders). It works on android emulator.

I'm not sure about where is a best place to add that lights' uniforms to scene graph (e.g. rootStateSet->addUniform(myLight0->positionUniform); ). For now, I just call it after creating every light. I think ShaderLight object should do it itself, but how can it get a StateSet to which uniforms should be added?

------------------
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[Chris Hanson]

Let me check with Thomas.

Post by Grigoriy Mylnikov
At the moment, I implemented ShaderLight class that extends osg::Light and
allows to use several point lights with per-pixel lighting (using my
shaders). It works on android emulator.
I'm not sure about where is a best place to add that lights' uniforms to
scene graph (e.g. rootStateSet->addUniform(myLight0->positionUniform); ).
For now, I just call it after creating every light. I think ShaderLight
object should do it itself, but how can it get a StateSet to which uniforms
should be added?
------------------
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--
Chris 'Xenon' Hanson, omo sanza lettere. ***@AlphaPixel.com
http://www.alphapixel.com/
Training • Consulting • Contracting
3D • Scene Graphs (Open Scene Graph/OSG) • OpenGL 2 • OpenGL 3 • OpenGL 4 •
GLSL • OpenGL ES 1 • OpenGL ES 2 • OpenCL
Legal/IP • Forensics • Imaging • UAVs • GIS • GPS •
osgEarth • Terrain • Telemetry • Cryptography • LIDAR • Embedded • Mobile •
iPhone/iPad/iOS • Android
@alphapixel <https://twitter.com/alphapixel> facebook.com/alphapixel (775)
623-PIXL [7495]

[Grigoriy Mylnikov]

Hi,

One more question. If I use gl_ModelViewMatrix in shaders to transform Light position, it gets transformed by both camera matrix and current node's matrix, that is not right.
Is there some build-in OSG uniform that holds only camera matrix or only model matrix? Or I should compute it and pass as my own uniform?

Thank you!

Cheers,
Grigoriy

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[Chris Hanson]

http://alphapixel.com/faqs/

src\osgUtil\SceneView.cpp(422): osg::Uniform* uniform =
_localStateSet->getOrCreateUniform(“osg_ViewMatrix”,osg::Uniform::FLOAT_MAT4);

src\osgUtil\SceneView.cpp(428): osg::Uniform* uniform =
_localStateSet->getOrCreateUniform(“osg_ViewMatrixInverse”,osg::Uniform::FLOAT_MAT4);

[Grigoriy Mylnikov]

Thank you, it works.

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