Hi Jordi,
Thank You very much for an example. I will give it a try by the end of the
week, as now I have lot of work to do with my PhD. If there would be any
problems I will ask further questions:)
Jordi Torres wrote:
> Hi Mateusz,
>
>
> Take in mind that 1D textures are limited to 8192 texels, if you need more
> you should use a TextureBufferObject. I've attached a simple example getting
> postions from a texture 1D. The TransferFunction used is not necessary.
>
>
> Hope it helps.
>
>
>
> 2013/6/20 Mateusz Janiak < ()>
>
> > Hi,
> >
> > I have a large static scene to render - it will not change in time. It can
> > contain even 1M spheres representing atoms in a particular material. I have
> > read a lot about instanced drawing and went through examples:
> > osgdrawinstanced
> > osgshaders
> >
> > but I can not to figure out how can I pass world positions for my sphere
> > prototype instances. I am rather not familiar with plain OpenGL and GLSL,
> > but what I have figured out till now is that I have to follow seweral steps
> > in general:
> > 1. Create my geometry drawable (simple sphere in my case using VBO)
> > 2. Create vertex shader program tha would populate my sphere prototype on
> > GPU side with defined number of instances
> > 3. Attach to vertex shader a buffer? texture? some data representing
> > positions of instances of this particular sphere type in world.
> > 4. Sample buffer, texture with respect to gl_InstanceID to obtain sphere
> > position at VS side
> >
> > I think I could perform such operation for each sphere type in scene
> > separately as there would be about 5 different spheres (radius). Is this
> > correct approach? Or I should avoid creating several independent programs
> > and try to create one doing all the stuff for different spheres?
> >
> > I would appriciate if anyone could guide me through process of binding
> > sphere`s world positions to vertext. As mentioned I was trying to attach to
> > my geometry 1D texture filled with positions of sphere instances and read
> > it in shader according to gl_InstanceID for obtaning proper position,
> > hovewer I am doing something wrong and I see just one sphere with strange
> > colors on it. I think my sampling and binding fails but I have no ide how
> > could I investigate the problem and "debug" shader if it is even posiible.
> >
> > I will just attach fragments of code I think are crucial for this task:
> > VS code
> >
> > Code:
> > #version 330 core
> > uniform sampler1D tex;
> > uniform int texSize;
> > void main(void) {
> > /* fetch instance position from texture buffer and add the local vertex
> > coordinate to it ? using gl_InstanceID and texSize to properly determine
> > position of my instance coordinates*/
> > vec4 ObjectSpacePosition = texture(tex, gl_InstanceID / float(texSize)) +
> > vec4(gl_Vertex, 1.0);
> > ObjectSpacePosition.w = 1.0;
> >
> > /* transform into view space */
> > vec4 ViewSpacePosition = gl_ModelViewMatrix * ObjectSpacePosition;
> >
> > /* transform into clip space */
> > gl_Position = gl_ProjectionMatrix * ViewSpacePosition;
> > }
> >
> >
> >
> > Texture with position coordinates:
> >
> >
> > Code:
> > unsigned int instCount = ...;
> >
> > osg::Image* image = new osg::Image;
> >
> > // allocate the image data, instCount x 1 x 1 with 4 rgba floats -
> > equivalent to a Vec4!
> > image->allocateImage(instCount,1,1,GL_RGBA,GL_FLOAT);
> > image->setInternalTextureFormat(GL_RGBA);
> >
> > // fill in the image data
> > osg::Vec4* dataPtr = (osg::Vec4*)image->data();
> > for( osg::Vec3 pos : InstancePositions )
> > {
> > *dataPtr++ = osg::Vec4(pos, 1.0);
> > }
> >
> > osg::Texture1D* texture = new osg::Texture1D;
> > texture->setWrap(osg::Texture1D::WRAP_S,osg::Texture1D::WrapMode::REPEAT);
> > texture->setFilter(osg::Texture1D::MIN_FILTER,osg::Texture1D::NEAREST);
> > texture->setImage(image);
> >
> >
> >
> > And finally state set for geometry:
> >
> >
> > Code:
> > osg::ref_ptr< osg::StateSet > s = new osg::StateSet;
> >
> > // setting proper GL modes
> > s->setMode(GL_CULL_FACE,osg::StateAttribute::ON);
> > s->setMode(GL_LIGHTING, osg::StateAttribute::ON);
> > s->setMode(GL_RESCALE_NORMAL, osg::StateAttribute::ON);
> > s->setMode(GL_DEPTH_TEST, osg::StateAttribute::ON);
> > s->setMode(GL_BLEND, osg::StateAttribute::OFF);
> >
> > //create shader
> > osg::ref_ptr< osg::Shader > nVertexShader = new osg::Shader();
> > nVertexShader->setType( osg::Shader::VERTEX );
> > nVertexShader->setShaderSource( ... );
> >
> > osg::ref_ptr< osg::Program > program = new osg::Program();
> > program->addShader( nVertexShader.get() );
> >
> > s->setAttribute( program.get(), osg::StateAttribute::ON |
> > osg::StateAttribute::PROTECTED );
> >
> > //set texture for node which I want to sample in shader for positions
> > s->setTextureAttribute(0,texture,osg::StateAttribute::OVERRIDE);
> > s->setTextureMode(0,GL_TEXTURE_1D,osg::StateAttribute::ON|osg::StateAttribute::OVERRIDE);
> > s->setTextureMode(0,GL_TEXTURE_2D,osg::StateAttribute::OFF|osg::StateAttribute::OVERRIDE);
> > s->setTextureMode(0,GL_TEXTURE_3D,osg::StateAttribute::OFF|osg::StateAttribute::OVERRIDE);
> > // size of texture so I can rescale my gl_InstanceID to proper float value
> > in shader for texture sampling
> > osg::Uniform* texSize = new osg::Uniform("texSize",instCount);
> > s->addUniform(texSize);
> > //sets the texture? not sure about this line
> > s->addUniform(new osg::Uniform("tex", 0));
> >
> >
> >
> >
> > I have read about uniform arrays but they have some limitations as far as I
> > have diged about them, so I thought this would be a better way to load
> > texture once to GPU and then use it all the time. Once again - if someone
> > keen with VS, OpenGL, GLSL could guide me with this task I would be very
> > gratefull. I think such example could be also a good startup for others
> > rendering such big scenes if provided general steps are posiible at all.
> >
> > Thank you!
> >
> > Cheers,
> > Mateusz[/code]
> >
> > ------------------
> > Read this topic online here:
> > http://forum.openscenegraph.org/viewtopic.php?p=54715#54715
> > (http://forum.openscenegraph.org/viewtopic.php?p=54715#54715)
> >
> >
> >
> >
> >
> > _______________________________________________
> > osg-users mailing list
> > ()
> > http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
> > (http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org)
> >
>
>
>
> --
> Jordi Torres
>
> ------------------
> Post generated by Mail2Forum
------------------
Read this topic online here:
http://forum.openscenegraph.org/viewtopic.php?p=55787#55787
_______________________________________________
osg-users mailing list
[email protected]
http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
