Re: [osg-users] Shadows on "invisible" objects

[Trajce Nikolov NICK]

Hi Allessandro,

my case is a bit different, it is about invisible object to cast shadows on
visible objects. The second link with the shader hints gave me an idea
though...

Thank you so much for the links !!

Nick

On Thu, Mar 30, 2017 at 10:05 AM, Alessandro Terenzi 
wrote:

> Hi Nick,
> as far as I understand you'd like to cast shadows onto a geometry that is
> kind of invisible but still can receive shadows, is this right?
>
> Have you already read these?
>
> http://forum.openscenegraph.org/viewtopic.php?t=8912;
> highlight=invisible+shadow
>
> http://forum.openscenegraph.org/viewtopic.php?t=12628;
> highlight=invisible+shadow
>
> Hope these will help.
> Alessandro
>
> On Tue, Mar 28, 2017 at 9:06 AM, Trajce Nikolov NICK <
> trajce.nikolov.n...@gmail.com> wrote:
>
>> Hi Community,
>>
>> I am trying to solve a problem where my scene is with shadow caster model
>> where I want to see only the shadows and have the shadow caster model
>> invisible. What would be the node masks game to achieve this? or some other
>> solution?
>>
>> Thanks a bunch as always
>>
>> Nick
>>
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>> trajce nikolov nick
>>
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Re: [osg-users] Shadows on "invisible" objects

[Alessandro Terenzi]

Hi Nick,
as far as I understand you'd like to cast shadows onto a geometry that is
kind of invisible but still can receive shadows, is this right?

Have you already read these?

http://forum.openscenegraph.org/viewtopic.php?t=8912=invisible+shadow

http://forum.openscenegraph.org/viewtopic.php?t=12628=invisible+shadow

Hope these will help.
Alessandro

On Tue, Mar 28, 2017 at 9:06 AM, Trajce Nikolov NICK <
trajce.nikolov.n...@gmail.com> wrote:

> Hi Community,
>
> I am trying to solve a problem where my scene is with shadow caster model
> where I want to see only the shadows and have the shadow caster model
> invisible. What would be the node masks game to achieve this? or some other
> solution?
>
> Thanks a bunch as always
>
> Nick
>
> --
> trajce nikolov nick
>
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> http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
>
>
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Re: [osg-users] Shadows on invisible objects

[Juan Cruz]

Thank you both for your replies.  I figured out how to do it with the help of 
Terry's post.  I'm putting my answer here in case anyone else comes across the 
same problem.  

I sub-classed osg.ShadowMap, and set a new custom fragment shader code.  I 
created a flag (which I call 'ghostObject') to mark those nodes for which the 
effect will be applied.  I set the flag on each node using:

 node.getOrCreateStateSet().addUniform(osg.Uniform('ghostObject', True))

If the flag is set, the shader will set the alpha of every pixel to 0, except 
those pixels that lie inside a shadowed area.  If the flag is not set, the 
shader will just darken shadowed areas.


Code:
shaderSource = 
uniform sampler2D osgShadow_baseTexture; \m
uniform sampler2DShadow osgShadow_shadowTexture; \n
uniform vec2 osgShadow_ambientBias; \n
uniform bool ghostObject;\n
   
void main(void) \n
{\n
 
vec4 shadowProj = shadow2DProj( osgShadow_shadowTexture, gl_TexCoord[1] 
);\n

gl_FragColor = gl_Color * texture2D( osgShadow_baseTexture, 
gl_TexCoord[0].xy );\n

if(ghostObject  shadowProj.x  0.5 )\n
gl_FragColor.w = 0.0;\n
else if( shadowProj.x  0.5 ){\n
gl_FragColor.x = gl_FragColor.x * 0.5;\n
gl_FragColor.y = gl_FragColor.y * 0.5;\n
gl_FragColor.z = gl_FragColor.z * 0.5;\n
}\n

 }\n



Thank you!

Cheers,
Juan
Code:




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Re: [osg-users] Shadows on invisible objects

[Robert Osfield]

Hi Juan,

It's hard to know exactly what you mean by invisible objects, or how
they might recieve a shadow.

Could you take a step back and explain at a high level what you are
trying to achieve.

Robert.

On 18 May 2013 13:03, Juan Cruz j_...@hotmail.com wrote:
 Hi,

 I'm creating a visualization where it is critical for some invisible objects 
 to be able to receive shadows on them.  I know this sounds physically 
 impossible, but I hope it is possible on a virtual environment.  Is there any 
 way of achieving this in OSG?  Perhaps using shaders?

 Thank you!

 Cheers,
 Juan

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Re: [osg-users] Shadows on invisible objects

[Terry Welsh]

This sounds reasonable. If all your objects (including the invisible
ones) have the appropriate NodeMask bit set, then they can all be
rendered into your shadow map. Then when you render the final scene,
you would need a specialized shader for rendering the invisible
objects. This shader would only render pixels that are in shadow; you
could render just a transparent gray for the shadowed pixels that you
keep.
--
Terry Welsh
www.reallyslick.com


 Hi,

 I'm creating a visualization where it is critical for some invisible objects 
 to be able to receive shadows on them.  I know this sounds physically 
 impossible, but I hope it is possible on a virtual environment.  Is there any 
 way of achieving this in OSG?  Perhaps using shaders?

 Thank you!

 Cheers,
 Juan

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Re: [osg-users] Shadows on invisible objects

[Paul Martz]

On 8/5/2011 11:03 AM, Alessandro Terenzi wrote:

Hi,
I want to make an object invisible but, nonetheless, I also want it to receive 
shadows, any suggestion?

By the way, I'm using the ShadowMap technique to implement shadows.

Thanks.
Alessandro



When I use depth map shadows, I use a fragment shader to sample the depth 
texture. If I wanted to see only the shadow areas but not the lit areas, I'd 
just add the appropriate conditional call to discard.


Hope that helps,

--
  -Paul Martz  Skew Matrix Software
   http://www.skew-matrix.com/

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Re: [osg-users] Shadows on invisible objects

[Chris 'Xenon' Hanson]

On 8/5/2011 11:03 AM, Alessandro Terenzi wrote:
 Hi,
 I want to make an object invisible but, nonetheless, I also want it to 
 receive shadows, any suggestion?

  Receive? That makes no sense. Its appearance can't be altered by a shadow if 
it has no
appearance.

-- 
Chris 'Xenon' Hanson, omo sanza lettere. xe...@alphapixel.com 
http://www.alphapixel.com/
  Digital Imaging. OpenGL. Scene Graphs. GIS. GPS. Training. Consulting. 
Contracting.
There is no Truth. There is only Perception. To Perceive is to Exist. - 
Xen
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Re: [osg-users] Shadows on invisible objects

[Alessandro Terenzi]

Paul Martz wrote:
 
 When I use depth map shadows, I use a fragment shader to sample the depth 
 texture. If I wanted to see only the shadow areas but not the lit areas, I'd 
 just add the appropriate conditional call to discard.
 


Thanks Paul, your suggestion is very helpful, anyway I wonder if there exists 
also a way to achieve the same result without relying on shaders...for example, 
in the past I used the ColorMask to create an 'invisible' object that was able 
to hide other objects (its shape and volume was reveiled if other objects moved 
behind it, even though it was not visible in the scene). You can also pick such 
kind of invisible objects, so, maybe, something similar can be done also with 
shadows.

Basically I'm looking for a way to reveil the shape/volume of an invisible 
object by means of shadows casted onto it, I know that this may make no sense 
from a physical point of view, but we're in the CG world where only imagination 
is the limit, aren't we?

Cheers.
Alessandro

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