[osg-users] Changes in osgVolume from 3.0 to 3.4

[Robert Osfield]

Hi Alex,

The blending difference might be down to a bug fix elsewhere in the
OSG.  Have a look at yesterdays discussion "osgViewer/Renderer ctor
set wrong defaults for SceneView", in particular my replies that
explain how a bug fix (in OSG-3.2 onwards) to the way that global
State is managed reveals a deficiency in the viewer set up.

As the light direction issue, the new way is more general purpose, the
old behaviour isn't required, the old shaders aren't maintained.  If
you want the old shaders and uniform set up you'll need to write these
yourself, or just adopt the new approach and have your viewer
manipulate the main light source using the viewer's Light or an
osg::LightSource placed in the scene.

Robert.

osg-users
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On 3 February 2016 at 21:11, Alex Taylor <alextaylor at gmail.com> wrote:
> Robert,
>
> Thanks. There are two main culprits the behavior change I was seeing. The
> first is that for some reason, between OSG 3.0 and 3.4, I now need to
> explicitly set a BlendFunc. With the exception of MIP, it looks like the
> rest of osgVolume just renders with a default BlendFunc and doesn't
> explictly set anything.
>
> I found that by setting
>
>  stateset->setAttribute(new osg::BlendFunc(GL_SRC_ALPHA,
> GL_ONE_MINUS_SRC_ALPHA), osg::StateAttribute::ON);
>
> There is a second issue I want to ask about:
>
> It looks to me there was a change to the shaders I'm using regarding the
> position of the light source between OSG 3.0 and OSG 3.4:
>
> https://github.com/openscenegraph/osg/commit/4525ec49a386b48608fdb3107033a1c915d928e6
>
> The change is to honor the lightDirection from GL_LIGHT0 rather than use the
> eye direction as the direction of the light source.
>
> If I wanted to get the old behavior of using the eyeDirection, is there an
> easy way to go about that?
>
> Thanks,
>
> Alex
>
>
> On Thu, Jan 28, 2016 at 3:16 PM Robert Osfield <robert.osfield at gmail.com>
> wrote:
>>
>> Hi Alex,
>>
>> There were quite a few improvements to osgVolume between OSG-3.0 and
>> OSG-3.4, both in shaders and the introduction of the new MultiPassTechnique.
>> One thing to look at with your own setup is that you aren't picking up on
>> old
>>  shaders such as by having your own path to old shaders.
>>
>> It's quite a while since I did the work on osgVolume, around two years, so
>> won't be able to be specific without viewing code and being able to
>> reproduce the problems you are seeing first hand.
>>
>> Robert.
>>
>> On 28 January 2016 at 15:25, Alex Taylor <alextaylor at gmail.com> wrote:
>>>
>>> Hi,
>>>
>>> I'm working on upgrading the OSG version used in the product I work on.
>>> When OSG is upgraded with the same client code, I'm noticing differences is
>>> the way my volumes are rendered with all of the rendering algorithms that I
>>> can't explain. I've fixed the parameters I'm using to define the osgVolume
>>> in both versions, so it can't be a matter of picking up a different default
>>> option for a parameter.
>>>
>>> OSG 3.4 Fixed Function
>>>
>>> OSG 3.0 Fixed Function
>>>
>>>
>>> OSG 3.4 Ray Traced Lit
>>>
>>>
>>> OSG 3.0 Ray Traced Lit
>>>
>>>
>>>
>>> OSG 3.4 Isosurface
>>>
>>> OSG 3.0 Isosurface
>>>
>>>
>>> In the Ray Traced cases, I'm using the properties:
>>>
>>> AlphaFunc = 0.02;
>>> SampleDensity = 0.005;
>>>
>>> I'm using setting the TransferFunctionProperty, so I'm using the shaders
>>> to do the alpha/color mapping.
>>>
>>> For the FixedFunctionTechnique, I'm using AlphaFunc = 0.02, and using the
>>> applyTransferFunction function to obtain an RGBA mapped osg::Image buffer.
>>>
>>> It's very possible that the upgrade to 3.4 has changed something else in
>>> my overall use of OSG elsewhere in the pipeline, unrelated to osgVolume,
>>> that is causing this issue. That said, I thought i'd ask if visually anyone
>>> has a guess it what might have changed between osg 3.0 and osg 3.4 that
>>> might explain these visual differences.
>>>
>>> Thanks for your help,
>>>
>>> Alex
>>>
>>>
>>>
>>> _______________________________________________
>>> osg-users mailing list
>>> osg-users at lists.openscenegraph.org
>>> http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
>>>
>>
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