Hi Eric,
You OpenGL code looks wrong, you shouldn't unbind the FBO then do
glReadPixels as this will mean that you are reading from the main
frame buffer not the FBO.
If you look at the RenderStage.cpp RenderStage::drawInner you'll see
the where is unbinds the FBO:
if (fbo_supported)
{
// switch of the frame buffer object
fbo_ext->glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);
doCopyTexture = true;
}
So the only thing left to clear up was the double call, which lines of
OSG code are you thinking of?
Robert.
On 2/8/07, E. Wing <[EMAIL PROTECTED]> wrote:
I am getting a strange rendering problem using Framebuffer Objects and
Renderbuffers. I am trying to render to an offscreen image
(osg::Image). I then utilize that image for a Cocoa drag-and-drop
effect. It seems that in some situations, parts of my onscreen views
get erased partially or completely.
I tried reproducing the problem in raw OpenGL/Cocoa. I thought I had
reproduced it, but it turns out that I missed two gl framebuffer
commands which I was corrected by the Mac-OpenGL list and I am now
unable to reproduce the problem.
So my problem seems to be OSG related. I still can't tell if it is a
driver bug or OSG miscalling OpenGL bug so I'm trying to understand
the OSG framebuffer code.
I've posted before about using osg::Camera and FBOs. With a SceneView
or SimpleViewer, I was told that render to offscreen buffer wouldn't
work with the root camera, so I should temporarily insert a second
camera node between the root camera and the scene root. This seemed to
solve my problem, but I've recently discovered the disappearing
problem.
So I've been stepping through FrameBufferObject.cpp. Can somebody
explain why I'm seeing the sequence I see?
In raw OpenGL, I expect this short sequence of commands:
glGenFramebuffersEXT(1, & fboID);
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, frame_buffer);
glGenRenderbuffersEXT(1, &objectID);
glBindRenderbufferEXT(GL_RENDERBUFFER_EXT, objectID);
glRenderbufferStorageEXT(GL_RENDERBUFFER_EXT, GL_RGBA, width, height);
glFramebufferRenderbufferEXT(GL_FRAMEBUFFER_EXT,
GL_COLOR_ATTACHMENT0_EXT, GL_RENDERBUFFER_EXT, objectID);
// Draw OpenGL scene here
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0); // make window the target
glReadPixels(...);
But with OSG I'm seeing some extra stuff:
// simpleViewer->frame() called here which starts sequence
glGenFramebuffersEXT(1, & fboID); // fboID=1
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fboID); // fboID=1
glGenRenderbuffersEXT(1, &objectID); // objectID=1
glBindRenderbufferEXT(GL_RENDERBUFFER_EXT, objectID); // objectID=1
glRenderbufferStorageEXT(GL_RENDERBUFFER_EXT, GL_RGBA, width, height);
glFramebufferRenderbufferEXT(GL_FRAMEBUFFER_EXT,
GL_COLOR_ATTACHMENT0_EXT, GL_RENDERBUFFER_EXT, objectID); //
objectID=1
glGenRenderbuffersEXT(1, &objectID); // objectID=2, (why do we have
another renderbuffer?)
glBindRenderbufferEXT(GL_RENDERBUFFER_EXT, objectID); // objectID=2
glRenderbufferStorageEXT(GL_RENDERBUFFER_EXT, GL_RGBA, width, height);
glFramebufferRenderbufferEXT(GL_FRAMEBUFFER_EXT,
GL_COLOR_ATTACHMENT0_EXT, GL_RENDERBUFFER_EXT, objectID); //
objectID=2
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fboID); // fboID=1 (why not 0?)
// frame() returns around here
So why am I seeing a second renderbuffer (and maybe why am I not
seeing a second framebuffer)? And why does glBindFramebufferEXT get
called again?
Could this strange sequence of commands be causing the rendering
problems I'm seeing? (I'm not getting any errors from glGetError() by
the way.)
Thanks,
Eric
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