Hi
On 8/30/07, 赵明伟 <[EMAIL PROTECTED]> wrote:
>
> En. Another problem I think there will be. many 3d model files may
> have reference to image on local disk. so how can I save the image(write a
> NodeVisitor is a solution?), and then How I read that.
>
> ---MingWei---
>
I see two solutions to your problem:
1) use osgconv to convert your model from its original format to the .ive
format (OSG's binary format). The .ive file is standalone and contains
everything you need - i.e. no external textures. Then you save this model in
your database and use the previous technique with the .ive plugin rather
than 3ds or openflight.
2) install an osgDB::Registry::ReadFileCallback before you load your model
file. Override the readImage() functions and have them read the textures
from your database using the previous technique rather than on the local
disk. If many of your models reference the same texture, this might be lead
to a higher performance since it benefits from osgDB::Registry's caching
mechanism (though I don't know whether multiple .ive files can share the
same texture)
Hope this helps
Thibault
在2007-08-30，"赵明伟" <[EMAIL PROTECTED]> 写道：
>
>
> Thank you very much. That's just what I meed.
> Thanks again for your help.
>
> ---MingWei---
>
>
>
> 在2007-08-29，"Thibault Genessay" <[EMAIL PROTECTED]> 写道：
>
> Hi
>
> On 8/28/07, 赵明伟 <[EMAIL PROTECTED]> wrote:
> >
> > I find the ReadWriter's virtual function read/write Object/Image/Node
> > from file and also from the memory by istream. I think That's what I want.
> > But It seems to only the osg plugin implement the function completely.
> >
>
> I think we kinda float the same boat :)
>
> First, my situation: I have stuffed images in a database by loading the
> files into memory buffers, and saving them in my DB. The table has a row
> that contains the image name, extension (essential!) and the binary data
> (stored as a PostgreSQL 'bytea' data type). Until today, I was loading the
> row, saving it to a file and reloading it with osgDB::readImageFile(). This
> worked but was ugly.
>
> Now the solution I ended up with: of course, we want to load the images
> directly from memory. Idea: osg::ReaderWriter provides a virtual method
> readImage(std::istream& fin) that can read from streams. If we can create an
> ad-hoc stream from our memory buffer, we're done (provided that the specific
> plugins you are interested in, i.e. 3ds and OpenFlight, do implement this
> method). Now, the C++ does not have a built-in way to create a stream from a
> buffer. So, after googling for a couple of hours, I have written (ahem ...
> copy-pasted :) a custom std::streambuf that can read from our memory buffer.
> It goes like this:
>
> template <class cT, class traits = std::char_traits<cT> >
> class basic_membuf : public std::basic_streambuf<cT, traits> {
> public:
> basic_membuf(cT * mem, std::streamsize sz) {
> setg(mem, mem, mem + sz);
> }
> };
> typedef basic_membuf<char, std::char_traits<char> > membuf;
>
> [ Credits go to Dietmar Kühl. See the thread that comes first while
> searching 'memory mapped istream' in google groups for '
> comp.lang.c++.moderated'. ]
>
> Let's assume your image data is:
>
> char* memory_mapped_file = read_the_data_from_the_database();
> size_t length = ... // you have to know the size, but that should not be
> tricky
> const char* extension = "png"; // for instance
>
> Now, we can create a stream for our memory-mapped file:
>
> membuf my_buf(memory_mapped_file, length);
> std::istream stream(&my_buf);
>
> If we add the OSG stuff, we have the following function:
>
> osg::Image* getImageFromBuffer(char* buffer, size_t length, const char*
> extension)
> {
> osgDB::ReaderWriter* rw =
> osgDB::Registry::instance()->getReaderWriterForExtension(extension);
> if (rw)
> {
> membuf sb(buffer, length);
> std::istream stream(&sb);
> osgDB::ReaderWriter::ReadResult rr = rw->readImage(stream);
> return rr.takeImage();
> }
> }
>
>
> And you are done.
>
> Thibault
>
>
>
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