On 17 Sep 2013, at 19:47, Rick Armstrong <rick.armstr...@urbanrobotics.net> 

> Indeed, PNG would be ideal!
> > - if you have any interested in
> > doing this, I can point you at examples since the screenshot code was
> > converted to do the same thing recently -it's probably a couple of hours
> > hacking at most)
> I'd be happy to take a crack at it. This would be my first foray into the 
> FlightGear source tree, so a pointer to some sample code would be great.

Okay, various pieces:

        gui_funcs.cxx has the screenshot dumping code, especially the logic to 
run things safely via an OSG GraphicsContextOperation. Its run() virtual 
contains a call to: sg_glDumpWindow

which is defined in SimGear and does the actual reading of the frame-buffer and 
writing via:

        // dump the screen buffer to a png file, returns true on success 
        bool sg_glDumpWindow(const char *filename, int win_width, int 
                osg::ref_ptr<osg::Image> img(new osg::Image);
                img->readPixels(0,0, win_width, win_height, GL_RGB, 
                return osgDB::writeImageFile(*img, filename);

The trick will be to interface this with the jpg-httpd infrastructure. There's 
a problem I can see here - the osgDB API is very file orientated, but I assume 
you need the image data in memory to send down the HTTP socket. We might need 
to ask on the OSG mailing list if this can be done, otherwise you'd have to 
read the file back after writing it. This is little ugly but the file should be 
in the cache so probably no actual disk access happens.

Most of jpgfactory.cxx is irrelevant, I'd ignore it completely since it only 
deals with the tile-rendering (not needed these days since we can render big GL 
viewports natively) and the mechanics of running the image compressor. If you 
can plug the stuff you need into line 227 of jpg-httpd, I think you're good.

That's a very rough sketch based on ten minutes reading of course.

Note if you want actual good performance from this system, there's much smarter 
things that could be done, such as grabbing the frame buffer each normal 
rendering frame, instead of re-rendering the scene each time an HTTP get is 
received. That would need much more drastic changes to the system however.

As ever, any further questions, just ask.


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