Re: [osg-users] Issue adding transparency to a simple model

[Sergey Polischuk]

Hi,

If you can get by with rendering only first layer of transparency, or rendering 
all layers without respect to ordering (f.e. when all layers have low alpha 
values and/or close color values):
for 1st case - you can draw your model first only to depth buffer, then 2nd 
time only to color buffer with depth test set to EQUAL
for 2nd - you draw you model first only to color buffer, then only to depth 
buffer

Cheers,
Sergey.

04.07.2012, 00:06, Preet prismatic.proj...@gmail.com:
 Hi.

 I have a simple model I wanted to apply transparency to. I load the
 model data into a geometry node, and set my scene up. To get a
 transparent effect, I apply an alpha value to gl_FragColor in my
 fragment shader.

 The shaders are trivial:
 Vertex:
 void main()
 {
    gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
 }

 Fragment:
 void main()
 {
    gl_FragColor = vec4(1,0,0,0.5);
 }

 I get a strange output that sort of works, but renders a different
 result based on the camera position. It's hard to describe so I
 attached a short youtube clip. It seems like certain triangles are
 only rendered at certain camera angles.

 http://youtu.be/fQUFSff-uuU

 I played around with some of the settings I thought might be relevant
 but I still get the effect that the video shows.

 osg::StateSet *ss = geodeMesh-getOrCreateStateSet();
 ss-setAttributeAndModes(shProgram,osg::StateAttribute::ON);
 ss-setMode(GL_BLEND,osg::StateAttribute::ON);

   // options i tried changing around
 //    ss-setMode(GL_DEPTH_TEST,osg::StateAttribute::ON);
 //    ss-setMode(GL_DEPTH_WRITEMASK,osg::StateAttribute::OFF);
 //    ss-setMode(GL_CULL_FACE,osg::StateAttribute::OFF);
 //    ss-setRenderingHint(osg::StateSet::TRANSPARENT_BIN);

 Any advice would be appreciated.
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Re: [osg-users] Issue adding transparency to a simple model

[Preet]

Thanks Paul and Sergey

I'll try both methods.
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[osg-users] Issue adding transparency to a simple model

[Preet]

Hi.

I have a simple model I wanted to apply transparency to. I load the
model data into a geometry node, and set my scene up. To get a
transparent effect, I apply an alpha value to gl_FragColor in my
fragment shader.

The shaders are trivial:
Vertex:
void main()
{
   gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
}

Fragment:
void main()
{
   gl_FragColor = vec4(1,0,0,0.5);
}

I get a strange output that sort of works, but renders a different
result based on the camera position. It's hard to describe so I
attached a short youtube clip. It seems like certain triangles are
only rendered at certain camera angles.

http://youtu.be/fQUFSff-uuU

I played around with some of the settings I thought might be relevant
but I still get the effect that the video shows.

osg::StateSet *ss = geodeMesh-getOrCreateStateSet();
ss-setAttributeAndModes(shProgram,osg::StateAttribute::ON);
ss-setMode(GL_BLEND,osg::StateAttribute::ON);

  // options i tried changing around
//ss-setMode(GL_DEPTH_TEST,osg::StateAttribute::ON);
//ss-setMode(GL_DEPTH_WRITEMASK,osg::StateAttribute::OFF);
//ss-setMode(GL_CULL_FACE,osg::StateAttribute::OFF);
//ss-setRenderingHint(osg::StateSet::TRANSPARENT_BIN);

Any advice would be appreciated.
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Re: [osg-users] Issue adding transparency to a simple model

[Paul Martz]

What are you doing to ensure that the triangles are rendered in back-to-front 
order?
   -Paul


On 7/3/2012 2:06 PM, Preet wrote:

Hi.

I have a simple model I wanted to apply transparency to. I load the
model data into a geometry node, and set my scene up. To get a
transparent effect, I apply an alpha value to gl_FragColor in my
fragment shader.

The shaders are trivial:
Vertex:
void main()
{
gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
}

Fragment:
void main()
{
gl_FragColor = vec4(1,0,0,0.5);
}

I get a strange output that sort of works, but renders a different
result based on the camera position. It's hard to describe so I
attached a short youtube clip. It seems like certain triangles are
only rendered at certain camera angles.

http://youtu.be/fQUFSff-uuU

I played around with some of the settings I thought might be relevant
but I still get the effect that the video shows.

 osg::StateSet *ss = geodeMesh-getOrCreateStateSet();
 ss-setAttributeAndModes(shProgram,osg::StateAttribute::ON);
 ss-setMode(GL_BLEND,osg::StateAttribute::ON);

   // options i tried changing around
//ss-setMode(GL_DEPTH_TEST,osg::StateAttribute::ON);
//ss-setMode(GL_DEPTH_WRITEMASK,osg::StateAttribute::OFF);
//ss-setMode(GL_CULL_FACE,osg::StateAttribute::OFF);
//ss-setRenderingHint(osg::StateSet::TRANSPARENT_BIN);

Any advice would be appreciated.
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Re: [osg-users] Issue adding transparency to a simple model

[Preet]

On Tue, Jul 3, 2012 at 4:45 PM, Paul Martz pma...@skew-matrix.com wrote:
 What are you doing to ensure that the triangles are rendered in
 back-to-front order?
-Paul

Nothing! How can I preprocess the data to achieve that?
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Re: [osg-users] Issue adding transparency to a simple model

[Paul Martz]

If you're unable to decompose your con-convex model into convex components, then 
you'll need an order-independent solution such as depth peeling. One possible 
implementation of depth peeling in OSG is demonstrated with the osgoit example.

   -Paul


On 7/3/2012 3:10 PM, Preet wrote:

On Tue, Jul 3, 2012 at 4:45 PM, Paul Martz pma...@skew-matrix.com wrote:

What are you doing to ensure that the triangles are rendered in
back-to-front order?
-Paul


Nothing! How can I preprocess the data to achieve that?
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