Hi Robert,
I made a check yesterday. glCheckFramebufferStatusEXT(GL_FRAMEBUFFER_EXT)
fails if glDrawBuffer & glReadBuffer are not set ot GL_NONE.
Look at GL_EXT_framebuffer_object extension description
http://oss.sgi.com/projects/ogl-sample/registry/EXT/framebuffer_object.txt
Usage Example (7):
(7) Render to depth texture with no color attachments
// Given: depth_tex - TEXTURE_2D depth texture object
// fb - framebuffer object
// Enable render-to-texture
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fb);
// Set up depth_tex for render-to-texture
glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT,
GL_DEPTH_ATTACHMENT_EXT,
GL_TEXTURE_2D, depth_tex, 0);
// No color buffer to draw to or read from
glDrawBuffer(GL_NONE);
glReadBuffer(GL_NONE);
// Check framebuffer completeness at the end of initialization.
CHECK_FRAMEBUFFER_STATUS();
<draw something>
// Re-enable rendering to the window
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);
glBindTexture(GL_TEXTURE_2D, depth_tex);
<draw to the window, reading from the depth_tex>
Cheers,
Wojtek
----- Original Message -----
From: "Wojciech Lewandowski" <[email protected]>
To: "OpenSceneGraph Users" <[email protected]>
Sent: Friday, July 24, 2009 4:25 PM
Subject: Re: [osg-users] Frame rates vary dramatically across runs
Hi Robert,
I've just has a look at your changed RenderStage. The changed code is
below. Is there a reason why the #if !FORCE_COLOR_ATTACHMENT which
disables the draw and read buffer is done after the FBO apply? I
looks to me that one could simply have an #ifdef/#else. I do also
wonder whether this is glDrawBuffer( GL_NONE ); etc. is even needed as
well - as wouldn't the Camera provide the appropriate settings via the
Read and DrawBuffer fields.
Frankly, this is something that puzzles me as well. I wrote this code only
to test if color attachment enforcement could be easily removed. It was
never intended as formal submission. It did it a year ago and I do not
remember why I have added glDrawBuffer( GL_NONE ); glReadBuffer( GL_NONE )
calls. I suppose I did it because original attempt did not work as
intended.
Ok I think I recall what was my goal. If there was no color attachment I
wanted to make sure glDrawBuffer and glReadBuffer are set to NONE because
otherwise OpenGL would assume that they are set to colorbuffers of
backbuffer/frontbuffer. And I did it after fbo->apply because I thought
that fbo->apply may call these functions with other flags.
It needs to be verified if I was right and this part was really needed. As
I said before this was not intended as submission and I had not make
serious study of its implications. I may try to look at this topic again
in next week.
Wojtek
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