Introduction

A demonstration of using the current rendered opengl screen as a texture within the same scene.

This is a video of this program and another feedback program in action:

http://video.google.com/videoplay?docid=-4613378742254751736

Windows Instructions

Download the executable:

http://binarymillenium.googlecode.com/svn/trunk/osg_feedback/CYGWIN32.Opt/osgprerender.exe

Unzip the required Cygwin and OSG libraries into the same directory:

http://binarymillenium.googlecode.com/files/cyg_osg_misc_dlls.zip

http://binarymillenium.googlecode.com/files/cyg_osg_1_2_plugins.zip

You'll need some kind of loadable content to be able to see anything, try

http://www.openscenegraph.org/downloads/data/OpenSceneGraph-Data-1.1.zip

or something else.

Run cmd.exe and cd into the proper directory.

Run osgprerender.exe osgcool.osg (where osgcool.osg could be any supported 3D model to be used in the scene) or use the following to take the texture from the desktop: osgprerender.exe osgcool.osg --directwximage

Build From Source Instructions

Modified osgprerender source is here:

http://binarymillenium.googlecode.com/svn/trunk/osg_vertexprogramfeedback/

Details

I built this using OpenSceneGraph 1.2 in Cygwin.

See http://binarymillenium.blogspot.com/2007/02/screen-capture-with-wxwindows.html for details on the screen capture code.

The regular OpenGL context code is much simpler, it's done with

            image->readPixels( startx, 
                    starty,
                    tex_width, 
                    tex_height, 
                    GL_RGB,GL_UNSIGNED_BYTE);

Where image is an Osg::Image. It also has a callback and other details which are the same as in the osgprerender example, where I started from.

X11 screen capture and conversion to OSG::Image code:

Display *dpy;
dpy = XOpenDisplay(NULL);
XImage *ximage = NULL;


ximage = XGetImage(dpy, RootWindow(dpy, DefaultScreen(dpy)) ,
                 0, 0,
                 tex_width, tex_height, AllPlanes, ZPixmap);
if (!ximage) {
      std::cerr << "XGetImage failed" << std::endl;
} 

// std::cerr << ximage->red_mask << std::endl;

image->allocateImage(tex_width, tex_height, 1, GL_RGBA, GL_FLOAT);
float* img_data = (float*)image->data();
  
for (unsigned i = 0; (i < tex_height); i++) {
for (unsigned j = 0; (j < tex_width); j++) {
    int ind = i*tex_width + j;
   
    bool flip = ((i > tex_height/4-1) && (i < 3*tex_height/4) &&
                (j > tex_width/4-1)  && (j < 3*tex_width/4));
    flip = !flip;
    unsigned long thepix = XGetPixel(ximage, j,i); //ximage->data + ind*3; 
    unsigned long red = (thepix & ximage->red_mask) >> 16;
    unsigned long green = (thepix & ximage->green_mask) >> 8;
    unsigned long blue = (thepix & ximage->blue_mask) >> 0;

    float r = red / 255.0;
    float g = green / 255.0;
    float b = blue / 255.0;
    img_data[ind*4]   = flip ? r : 1-r;
    img_data[ind*4+1] = flip ? g : 1-g;
    img_data[ind*4+2] = flip ? b : 1-b;
    img_data[ind*4+3] = 1.0;

} 
}

XDestroyImage(ximage);