Re: [osg-users] Problems rendering to and capturing/readin GL_RGBA16

[Sergey Polischuk]

Hi,

 

iirc to use GL_RGB16I_EXT, you should set source format to GL_RGB_INTEGER_EXT

also this is unnormalized texture format, so afaik you should write to it corresponding values (like int(INT_MAX*value)) where value is original value in range 0..1

 

Also i've used 32float per channel images to read back data without any problems, but i didnt used textures with them, attaching osg::Image directly to camera buffer. You can try it this way, but it slow as hell (may be assigning pbo to image will speed up things, i didnt tried it as in my case great runtime speed wasnt needed).

 

17.03.2012, 00:22, "Chris Hanson" <xe...@alphapixel.com>:

  A specialized tool I'm working on needs to have a 16-bit Alpha channel for post-render analysis. I render to a screen-sized texture (1920x1080 NPOT) and then read it back to the CPU side and assess the values.

  I originally developed it with 8-bit per gun RGBA (32-bit total) where it works fine, but precision is very poor. I then switched my RTT camera destination texture to use GL_RGBA16:

RTTtex->setInternalFormat( GL_RGBA16 );

RTTtex->setSourceFormat(GL_RGBA);

RTTtex->setSourceType(GL_UNSIGNED_SHORT);

  This seems to work lovely, but now reading back to the texture and fetching pixels from the texture seems problematic.

  I capture with a post-draw callback (m_tex is the RTT texture):

void CameraImageCaptureCallback::operator()( osg::RenderInfo& ri ) const

{

    osg::Image* image = m_tex->getImage();

    // Get the texture image.

    m_tex->apply( *( ri.getState() ) );

    image->readImageFromCurrentTexture( ri.getContextID(), false, GL_UNSIGNED_SHORT );

}

  I _think_ the UNSIGNED_SHORT is appropriate here (it was UNSIGNED BYTE when I was using regular 8-bit-per-channel rendering).

  To run this callback, I:

  osg::ref_ptr< CameraImageCaptureCallback > captureCB;

  outputImage = new osg::Image;

  outputImage->setPixelFormat(GL_RGBA);

  outputImage->setDataType(GL_UNSIGNED_SHORT); // different when in 8-bit mode

  osg::Texture2D *accumTex = GetAccumulationTexture(); // this is the texture that rendering writes to

  accumTex->setImage( outputImage );

           captureCB = new CameraImageCaptureCallback(accumTex); 

  GetPrerenderCamera()->setPostDrawCallback( captureCB.get() );

  // Run the viewer one more time to capture to the attached image.

  vpEnv.viewer->frame();

  Later, I examine the image pixel by pixel with:

alpha = lessonOutput->getColor(xLoop, yLoop).a();

  All of this works dandy in 8-bit mode, but add 8 more bits and it goes to heck.

  This message:

http://forum.openscenegraph.org/viewtopic.php?t=9879

  leads me to believe that some parts of OSG may not be supporting GL_RGBA16 properly, and in fact, I don't see it listed in the tokens in Image::computeNumComponents() though less-well-known tokens like GL_RGB16I_EXT are there.

  I tried using GL_RGB16I_EXT as my RTT texture format, but OSG fails to setup the RTT FBO, so I didn't succeed with that avenue. I was able to use GL_RGB16F_ARB but it seemed to behave very oddly all around, often refusing to clear the buffer when told to, so I abandoned that.

  A I missing any steps to setup for a GL_RGBA16 texture? I got very confused around all of the formats and internal formats and knowing what I needed to preconfigure in the osg::Image versus what OSG was going to setup for me. After the readImageFromCurrentTexture

 call, the Image's pixelFormat is set to GL_RGBA16, which makes calls like getColor fail because GL_RGBA16 isn't recognized.

  Is there a better way to render to a 16-bit int format? Am I just missing a critical step?

-- 

Chris 'Xenon' Hanson, omo sanza lettere. xe...@alphapixel.com http://www.alphapixel.com/

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