[osg-users] Using RayTracedTechnique

[Alex Taylor]

For context, I come from an image processing and signal processing
background, so computer graphics and OSG are both new to me.

I'm trying to use osgVolume for volume rendering some data. The only real
example code I can find out there is the osgvolume example that ships with
OSG. I'm a bit confused about the usage model with the various
VolumeTechnique classes.

I'm working with GL_RGBA uint8 data. In my code, I define a function
createTexture3D that creates an osg::Image object. The image is defined as:

*        osg::ref_ptr<osg::Image> image_3d = new osg::Image;*
*        image_3d->allocateImage(nmSAFE_CAST(int, s_nearestPowerOfTwo),*
*                nmSAFE_CAST(int, t_nearestPowerOfTwo),*
*                nmSAFE_CAST(int, r_nearestPowerOfTwo),*
*                desiredPixelFormat, GL_UNSIGNED_BYTE);​*

When I started with a simple example, FixedFunctionTechnique rendered my
data as I expected. See fixedFunctionTechnique.png attached.

*osg::ref_ptr<osgVolume::VolumeTile> tile = new osgVolume::VolumeTile;*
*            volume->addChild(tile.get());*

*            osg::ref_ptr<osg::Image> image_3d =
createTexture3D(data,xfer_table);*

*            osg::ref_ptr<osgVolume::ImageLayer> layer = new
osgVolume::ImageLayer(image_3d.get());*

*            tile->setLayer(layer.get());*

*            tile->setVolumeTechnique(new
osgVolume::FixedFunctionTechnique());*

*            // FixedFunctionTechnique turns on GL_LIGHTING, which breaks
the color rendering.*
*            osg::StateSet* stateset = volume->getOrCreateStateSet();*
*            stateset->setMode(GL_LIGHTING,osg::StateAttribute::OFF |
osg::StateAttribute::OVERRIDE);*

*            // Our original implementation positioned the bbox [-0.5,0.5]
in each dimension.*
*            // FixedFunctionTechnique applies the locator matrix to the a
unit cube [0 1] in each dimension.*
*            // To get the equivalent spatial referencing, apply a
translation of -0.5 to each dimension.            *
*            osg::ref_ptr<osg::RefMatrix> matrix = new osg::RefMatrix();*
*            matrix->makeTranslate(-0.5,-0.5,-0.5);*

I attempted to modify this simple example to use RayTracedTechnique next.
When I do that, both the color and the opacity of my volume data is off. In
some cases, I see something on the screen (see attached screenshot, in
other cases, I don't see anything). I almost feel like somehow my data is
outside of an expected colormap/alphamap range, but I can't figure out
what's off. In this particular example with an engine block CT dataset and
a specific colormap/alphamap, I see what is shown in the attached
rayTracedTechnique.png. Here is a partial code listing based on the OSG
example:


* osg::ref_ptr<osg::Image> image_3d = createTexture3D(data,xfer_table);*

*            osg::ref_ptr<osgVolume::ImageLayer> layer = new
osgVolume::ImageLayer(image_3d.get());*

*            tile->setLayer(layer.get());*

*            osgVolume::SwitchProperty* sp = new osgVolume::SwitchProperty;*
*            sp->setActiveProperty(0);*

*            osg::TransferFunction1D::ColorMap colorMap;*
*            for (size_t r = 0; r < 256; ++r){*
*                size_t rowOffset = r*4;*
*                float red =
static_cast<float>(xfer_table[rowOffset])/255.0;*
*                float green =
static_cast<float>(xfer_table[rowOffset+1])/255.0;*
*                float blue =
static_cast<float>(xfer_table[rowOffset+2])/255.0;*
*                float alpha =
static_cast<float>(xfer_table[rowOffset+3])/255.0;*
*                colorMap[r] = osg::Vec4(red,green,blue,alpha);*
*            }*

*            osg::ref_ptr<osg::TransferFunction1D> transferFunction = new
osg::TransferFunction1D;*
*            transferFunction->assign(colorMap);*

*            float alphaFunc=0.02f;*
*            float sampleDensityWhenMoving = 0.02;*
*            osgVolume::AlphaFuncProperty* ap = new
osgVolume::AlphaFuncProperty(alphaFunc);*
*            osgVolume::SampleDensityProperty* sd = new
osgVolume::SampleDensityProperty(0.005);*
*            osgVolume::SampleDensityWhenMovingProperty* sdwm =
sampleDensityWhenMoving!=0.0 ? new
osgVolume::SampleDensityWhenMovingProperty(sampleDensityWhenMoving) : 0;*
*            osgVolume::TransparencyProperty* tp = new
osgVolume::TransparencyProperty(1.0);*
*            osgVolume::TransferFunctionProperty* tfp =
transferFunction.valid() ? new
osgVolume::TransferFunctionProperty(transferFunction.get()) : 0;*

*            // Standard config from osgVolume example*
*            osgVolume::CompositeProperty* cp = new
osgVolume::CompositeProperty;*
*            cp->addProperty(ap);*
*            cp->addProperty(sd);*
*            cp->addProperty(tp);*
*            if (sdwm) cp->addProperty(sdwm);*
*            // if (tfp) cp->addProperty(tfp);*

*            sp->addProperty(cp);*
*            sp->setActiveProperty(0); // For now, always use "Standard"
config*
*            layer->addProperty(sp);*

*            tile->setVolumeTechnique(new osgVolume::RayTracedTechnique());*

*            // FixedFunctionTechnique turns on GL_LIGHTING, which breaks
the color rendering.*
*            osg::StateSet* stateset = volume->getOrCreateStateSet();*
*            // stateset->setMode(GL_LIGHTING,osg::StateAttribute::OFF |
osg::StateAttribute::OVERRIDE);*

*            // Our original implementation positioned the bbox [-0.5,0.5]
in each dimension.*
*            // FixedFunctionTechnique applies the locator matrix to the a
unit cube [0 1] in each dimension.*
*            // To get the equivalent spatial referencing, apply a
translation of -0.5 to each dimension.*
*            osg::ref_ptr<osg::RefMatrix> matrix = new osg::RefMatrix();*
*            matrix->makeTranslate(-0.5,-0.5,-0.5);*

*            tile->setLocator(new osgVolume::Locator(*matrix));*

I've spent the last few hours toggling settings on/off. I thought I'd see
if anyone here has ideas, or how I would go about debugging why things
aren't rendering correctly.

I also have a specific question. When working with RGBA data, should I be
specifying a *osgVolume::TransferFunctionProperty*​, and should this
property be in the float [0,1] normalized range as shown in the OSG
example, or should it be in a range that matches my data? I'm a bit
confused about whether/why I need to specify the transfer function when my
RGBA texture already knows the color and opacity for each voxel sample.

Sorry for the very long email. I'd appreciate any help or pointers anyone
can provide.

Best,

Alex Taylor
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openscenegraph.org/pipermail/osg-users-openscenegraph.org/attachments/20151214/2f84c7e3/attachment-0002.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: rayTracedTechniqueSmall.jpg
Type: image/jpeg
Size: 78838 bytes
Desc: not available
URL: <http://lists.openscenegraph.org/pipermail/osg-users-openscenegraph.org/attachments/20151214/2f84c7e3/attachment-0004.jpg>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: fixedFunctionTechniqueSmall.jpg
Type: image/jpeg
Size: 64824 bytes
Desc: not available
URL: <http://lists.openscenegraph.org/pipermail/osg-users-openscenegraph.org/attachments/20151214/2f84c7e3/attachment-0005.jpg>