[osg-users] What is the right way to save a FBO texture to disk?

[John Kaniarz]

My program has 4 render to texture cameras that get composited into the frame buffer via custom shader. I want to make a screen capture of one of the texture as a response to an event.

Attaching an Image to the camera works, but it copies the data to system memory after every frame. Not just when I need it.

I tried calling camera->attach(image); viewer->frame(); osgDB::writeImageFile(image); camera->attach(texture); in my event handler, but the image saved was blank.

I also tried calling texture->setImage(image), but that image is never updated with fresh data.

I also tried calling osg::Image::readPixels() in a Camera::postDrawCallback. This doesn't work because RenderStage detaches the FBO before the callback and I get a screenshot of the framebuffer instead of the texture. Would calling RenderStage::setDisableFboAfterRender(false) fix this? Whats the place to call that function from. Will this screw something up when I try to render to the actual framebuffer?

Is there another option I haven't thought of? Perhaps manually attaching the FBO and calling readPixels?

Thanks,
John

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[Robert Osfield]

Hi John,

I haven't done what you want before but the way I'd tackle it would be
to use a Camera post draw callback to call
state.applyAttribute(texture); then
image->readImageFromCurrentTexture(..).

Robert.

[John Kaniarz]

Thanks, I'll try that. Do I need to unapply the texture state when I'm done?

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[Robert Osfield]

On 6 June 2012 15:20, John Kaniarz <john.k...@us.army.mil> wrote:
> Thanks, I'll try that. Do I need to unapply the texture state when I'm done?

In theory osg::State should unapply it next time it does an
State::apply() of the current state.

Robert.

[John Kaniarz]

It captured a texture, but not the texture I was looking for.


Code:
osg::State * state=renderInfo.getState();
state->applyAttribute(texture);
osg::Image *image=new Image();
image->readImageFromCurrentTexture(renderInfo.getContextID(),false,GL_UNSIGNED_BYTE);
osgDB::writeImageFile(*image,"snap.png");



I'm guessing I'm either using the wrong context ID, or that I'm not applying the texture in the right way.

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[Robert Osfield]

On 6 June 2012 15:57, John Kaniarz <john.k...@us.army.mil> wrote:
> It captured a texture, but not the texture I was looking for.
>
>
> Code:
> osg::State * state=renderInfo.getState();
> state->applyAttribute(texture);
> osg::Image *image=new Image();
> image->readImageFromCurrentTexture(renderInfo.getContextID(),false,GL_UNSIGNED_BYTE);
> osgDB::writeImageFile(*image,"snap.png");
>
>
>
> I'm guessing I'm either using the wrong context ID, or that I'm not applying the texture in the right way.
>

I'm afraid I have tried specifically what you are trying before so
can't help debug it. Perhaps others will have done something similar
and be able to help.

Robert.

[John Kaniarz]

I got it working. The issue is that readImageFromCurrentTexture() doesn't support TextureRectangle. I modified my program to use a Texture2D instead and it works now.

Adding TextureRectangle support to Image doesn't look like it would be too hard except that GL_TEXTURE_BINDING_RECTANGLE isn't a readily available constant. (it shows up in gl3.h in the 3.1 section, but I'm sure there's an earlier extension)

Thanks for the help,

John

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