OK, this is what I've done. I've Subclassed osg::Camera::DrawCallback and read
from the texture in the operator() using osg::Image::readPixels, with an
applied FBO with the texture i want to read from attached. The retrieved value
seems to be correct. The callback object is set as "final draw callback" in a
camera I create and add to the root of my scene graph.
Even though I am able to get the data I need this way, it seems to me that this
is not a good solution. The only reason why I create a "dummy" camera which
doesn't render anything is to get a valid osg::State object to apply the FBO in
operator(). There must be a better way to do this? This way I have to request a
value and wait untill the next frame to collect it (??) because readPixels is
called in the operator() which I can't call in the update traversal were I need
the value. "Warning: detected OpenGL error 'invalid enumerant' at after
RenderBin::draw(..)" is printed each frame when the camera in the scene graph.
class ReadBufferCallback: public osg::Camera::DrawCallback
{
public:
osg::Texture2D* tex;
osg::Image* image;
osg::FrameBufferObject* fbo;
osg::FrameBufferAttachment *fba;
ReadBufferCallback(osg::Texture2D *_tex){
tex = _tex;
image = new osg::Image;
fbo = new osg::FrameBufferObject();
fba = new osg::FrameBufferAttachment(tex);
fbo->setAttachment(osg::Camera::COLOR_BUFFER, *fba);
}
virtual void operator() (osg::RenderInfo& renderInfo) const
{
fbo->apply(*(renderInfo.getState()),
osg::FrameBufferObject::READ_FRAMEBUFFER);
image->readPixels(500, 500, 1, 1, GL_LUMINANCE,
GL_FLOAT);
float* height = (float*)image->data();
cout << "height: " << *height << endl;
}
};
//Added to root of scene graph
osg::Camera* HeightTile::getHeightSampleCamera()
{
osg::Camera* cam = new osg::Camera;
cam->setRenderOrder(osg::Camera::PRE_RENDER);
cam->setRenderTargetImplementation(osg::Camera::FRAME_BUFFER_OBJECT);
cam->setFinalDrawCallback(new ReadBufferCallback(m_elevation_tex));
return cam;
}
Any help is much appreciated!
Cheers,
Martin
------------------
Read this topic online here:
http://forum.openscenegraph.org/viewtopic.php?p=28777#28777
_______________________________________________
osg-users mailing list
[email protected]
http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
