Rendering offscreen with QGLWidget

[jcox23]

Hey,

I am wondering what is the proper way to implement offscreen "offline" rendering with QGLWidget. By "offline", I mean without displaying any GUI. The "online" mode works well,here is the code of the offscreen render method:

///////////////////////////////
// Render the scene into a png
///////////////////////////////
void GlView::renderOffScreen()
{
 
    // We need to have a valid openGL context
    makeCurrent();
 
    QGLFramebufferObject * fb = new QGLFramebufferObject(8000,1000, GL_TEXTURE_2D);
 
    // bind it and let's start drawing on it....
    fb->bind();
 
        glClear(GL_COLOR_BUFFER_BIT |GL_DEPTH_BUFFER_BIT);
 
        // this must be the same size as the FrameBuffer....
        glViewport(0, 0, 8000, 1000);
 
        glMatrixMode(GL_PROJECTION);
            glLoadIdentity();
 
            gluOrtho2D(camera->left(),
                       camera->right(),
                       camera->bottom(),
                       camera->top());
 
        glMatrixMode(GL_MODELVIEW);
            glLoadIdentity();
 
        // renderData........
        renderData();
 
    fb->release();
 
    // reset the viewport to its normal self :)
    glViewport(0, 0, viewport[2], viewport[3]);
 
    // get the fb into a QImage
    QImage tempImage = fb->toImage();
 
    // Delete the FB
    delete fb;
 
    // Save the image
    if ( !tempImage.save( "hello.png", "PNG") )
         return;
 
}

///////////////////////////////
// Render the scene into a png
///////////////////////////////
void GlView::renderOffScreen()
{

    // We need to have a valid openGL context
    makeCurrent();

    QGLFramebufferObject * fb = new QGLFramebufferObject(8000,1000, GL_TEXTURE_2D);

    // bind it and let's start drawing on it....
    fb->bind();

        glClear(GL_COLOR_BUFFER_BIT |GL_DEPTH_BUFFER_BIT);

        // this must be the same size as the FrameBuffer....
        glViewport(0, 0, 8000, 1000);

        glMatrixMode(GL_PROJECTION);
            glLoadIdentity();

            gluOrtho2D(camera->left(),
                       camera->right(),
                       camera->bottom(),
                       camera->top());

        glMatrixMode(GL_MODELVIEW);
            glLoadIdentity();

        // renderData........
        renderData();

    fb->release();

    // reset the viewport to its normal self :)
    glViewport(0, 0, viewport[2], viewport[3]);

    // get the fb into a QImage
    QImage tempImage = fb->toImage();

    // Delete the FB
    delete fb;

    // Save the image
    if ( !tempImage.save( "hello.png", "PNG") )
         return;

}

To copy to clipboard, switch view to plain text mode 

To have the "offline" version, I simply deleted the call to show on the main widget...
It works on Linux (even though you clearly the something is created then deleted), but not on win32.... so I wonder if there is a more proper solution to this.....

Thanks

[George Neil]

Hey,

I am wondering what is the proper way to implement offscreen "offline" rendering with QGLWidget. By "offline", I mean without displaying any GUI. The "online" mode works well,here is the code of the offscreen render method:

///////////////////////////////
// Render the scene into a png
///////////////////////////////
void GlView::renderOffScreen()
{
 
    // We need to have a valid openGL context
    makeCurrent();
 
    QGLFramebufferObject * fb = new QGLFramebufferObject(8000,1000, GL_TEXTURE_2D);
 
    // bind it and let's start drawing on it....
    fb->bind();
 
        glClear(GL_COLOR_BUFFER_BIT |GL_DEPTH_BUFFER_BIT);
 
        // this must be the same size as the FrameBuffer....
        glViewport(0, 0, 8000, 1000);
 
        glMatrixMode(GL_PROJECTION);
            glLoadIdentity();
 
            gluOrtho2D(camera->left(),
                       camera->right(),
                       camera->bottom(),
                       camera->top());
 
        glMatrixMode(GL_MODELVIEW);
            glLoadIdentity();
 
        // renderData........
        renderData();
 
    fb->release();
 
    // reset the viewport to its normal self :)
    glViewport(0, 0, viewport[2], viewport[3]);
 
    // get the fb into a QImage
    QImage tempImage = fb->toImage();
 
    // Delete the FB
    delete fb;
 
    // Save the image
    if ( !tempImage.save( "hello.png", "PNG") )
         return;
 
}

///////////////////////////////
// Render the scene into a png
///////////////////////////////
void GlView::renderOffScreen()
{

    // We need to have a valid openGL context
    makeCurrent();

    QGLFramebufferObject * fb = new QGLFramebufferObject(8000,1000, GL_TEXTURE_2D);

    // bind it and let's start drawing on it....
    fb->bind();

        glClear(GL_COLOR_BUFFER_BIT |GL_DEPTH_BUFFER_BIT);

        // this must be the same size as the FrameBuffer....
        glViewport(0, 0, 8000, 1000);

        glMatrixMode(GL_PROJECTION);
            glLoadIdentity();

            gluOrtho2D(camera->left(),
                       camera->right(),
                       camera->bottom(),
                       camera->top());

        glMatrixMode(GL_MODELVIEW);
            glLoadIdentity();

        // renderData........
        renderData();

    fb->release();

    // reset the viewport to its normal self :)
    glViewport(0, 0, viewport[2], viewport[3]);

    // get the fb into a QImage
    QImage tempImage = fb->toImage();

    // Delete the FB
    delete fb;

    // Save the image
    if ( !tempImage.save( "hello.png", "PNG") )
         return;

}

To copy to clipboard, switch view to plain text mode 

To have the "offline" version, I simply deleted the call to show on the main widget...
It works on Linux (even though you clearly the something is created then deleted), but not on win32.... so I wonder if there is a more proper solution to this.....

Thanks

Does anyone succeed in overcoming this issue ?

[caglarkavak]

does anyone find a solution?

[Dong Back Kim]

does anyone find a solution?

I was able to store rendering result into files in Windows 7. In the image file, I could see part of my rendering which means somehow there was some sort of modelview or projection corruption... I will keep testing and post more details.

Regards,
Dong Back Kim

[fAX]

Hi,

Did you manage to overcome that? I need to do a similar thing. Thanks!