Hi Mateusz,
I went fast thru your email. I have faced similar challenge in the past and
was able to resolve it with geometry shader. You pass only vertices (the
centers of the spheres) and you create the actual geometry on the GPU. Just
a fast hint from different perspective
Nick
On Tue, Aug 6, 2013 at 9:29 PM, Mateusz Janiak <mati_jan...@wp.pl> wrote:
> 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
>
>
>
>
>
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--
trajce nikolov nick
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