Volumetric lightshafts via GPU

Lexx · Post by **Lexx** » Sun Apr 06, 2008 3:00 pm

Hi guys
This is demo of gpu-based volumetric lightshafts, described by Kenny Mitchell (EA) in GPUGems3. Demo code and algo based on sources of Sebastien Hillaire (http://sebastien.hillaire.free.fr/demos ... godray.htm) and ported to Ogre by me.

pics:

source and demo(vs2010)
http://www.mediafire.com/?535a3bfv03286za
http://www.megaupload.com/?d=MG9J0HUN

As like Sebastien, i have found a bug with current code (just fly around model in scene and u'll see it). Kenny Mitchell write about this:

Code: Select all

when facing perpendicular to the source, the light's screen-space location can tend toward infinity and therefore lead to large separation between samples. This can be diminished by clamping the screen-space location to an appropriate guard-band region. Alternatively, the effect can be faded toward the perpendicular and is further decreased when using an occlusion method.

So, can anyone please tell me, how can i clamp screenspace light position? I'm lost with it...

spookyboo · Post by **spookyboo** » Sun Apr 06, 2008 3:07 pm

Very impressive!

Cobra8472 · Post by **Cobra8472** » Sun Apr 06, 2008 3:37 pm

Very Very impressive! Looks great

Brocan · Post by **Brocan** » Sun Apr 06, 2008 5:16 pm

Amazing!

Nauk · Post by **Nauk** » Sun Apr 06, 2008 5:24 pm

ph4t

Post by **sinbad** » Sun Apr 06, 2008 5:44 pm

Very nice, thanks for sharing!

As for clamping screen space light, can't you just use min/max/saturate?

Lexx · Post by **Lexx** » Sun Apr 06, 2008 7:10 pm

I was trying to clamp/saturate light position in screen space, but coordinates of light in screen space is totally wrong. They can be for example [-1, -1] / [1, 1] (in a corner on screen space plane), when nonclamped value is [475, 816, 700](some point on the screen, not in a corner).
For rprojection of light vector to screen space, i use:

Code: Select all

Ogre::Vector3 vCamPos = m_pMainCamera->getRealPosition();
Ogre::Vector3 vSunPos = m_pSunLight->getDerivedPosition();
Ogre::Vector3 camToLightVector = vSunPos - vCamPos;

Ogre::Vector3 lightInCamSpace;
Ogre::Vector3 hcsPosition = m_pMainCamera->getProjectionMatrix() * m_pMainCamera->getViewMatrix() * camToLightVector; 
lightInCamSpace.x = 0.5 - hcsPosition.x * 0.5f;
lightInCamSpace.x = 1.0 - lightInCamSpace.x;
lightInCamSpace.y = hcsPosition.y * 0.5f + 0.5;
lightInCamSpace.y = 1.0 - lightInCamSpace.y;
lightInCamSpace.z = camToLightVector.z;
fpParams->setNamedConstant("screenLightPos", lightInCamSpace);

This code worked, when angle between camera direction and light vector is smaller than 90 degree.
I have search this problem in gamedev.net, and found topic with a same (as i think) problem. Guys were discussing about some kind of "pre-perspective" and "post-perspective" projection state... My english is sux (as like a my math ^^), so i don't understand anything of those math terms...
So, any help is welcome!

PS: sorry for my evil english

David Lancaster · Post by **David Lancaster** » Mon Apr 07, 2008 1:05 am

Congrats that is amazing!

cybereality · Post by **cybereality** » Mon Apr 07, 2008 2:22 am

Wow, most impressive. This is the kinda stuff that makes ogre the best!

altren · Post by **altren** » Mon Apr 07, 2008 9:15 am

Looks really good. One strange thing is that if i don't see an part of object - I don't see its shadow, so when I see only small part of object - shadow is incorrect.

Jaiza · Post by **Jaiza** » Mon Apr 07, 2008 12:59 pm

wow! looks really neat

warmi · Post by **warmi** » Mon Apr 07, 2008 5:05 pm

Looks good but gee.. the download service is the worst I have ever seen.

It could serve as a study how to make your user life misreable ( which is probably the point , given that they have a paid service )

Lexx · Post by **Lexx** » Mon Apr 07, 2008 10:18 pm

altren:
>One strange thing is that if i don't see an part of object - I don't >see its shadow, so when I see only small part of object - shadow >is incorrect.

yep, there's a lot of bugs and errors in rendering algorithm, like:

- worked only for screen quad

Code: Select all

As occluding objects cross the image's boundary, the shafts will flicker, because they are beyond the range of visible samples. This artifact may be reduced by rendering an extended region around the screen to increase the range of addressable samples.
Kenny Mitchell(c)

- wrong depth intersection

this can be fixed with some kind of per-pixel depth checking

- wrong code for projection of light vector to screen-space

i don't know how to fix this...

- for rendering black non-textured objects of the scene i use evil external technique with vertex shader... :/

etc.. So, there's a lot of space for optimization

broli · Post by **broli** » Mon Apr 07, 2008 11:27 pm

When does that last issue arise? Also what editor is that in the background :p.

detox · Post by **detox** » Tue Apr 08, 2008 3:16 pm

Very nice work. Thank you for sharing the code!

jingjie · Post by **jingjie** » Wed Apr 30, 2008 5:37 am

Lexx wrote:I was trying to clamp/saturate light position in screen space, but coordinates of light in screen space is totally wrong. They can be for example [-1, -1] / [1, 1] (in a corner on screen space plane), when nonclamped value is [475, 816, 700](some point on the screen, not in a corner).
For rprojection of light vector to screen space, i use:
Code: Select all
Ogre::Vector3 vCamPos = m_pMainCamera->getRealPosition();
Ogre::Vector3 vSunPos = m_pSunLight->getDerivedPosition();
Ogre::Vector3 camToLightVector = vSunPos - vCamPos;

Ogre::Vector3 lightInCamSpace;
Ogre::Vector3 hcsPosition = m_pMainCamera->getProjectionMatrix() * m_pMainCamera->getViewMatrix() * camToLightVector; 
lightInCamSpace.x = 0.5 - hcsPosition.x * 0.5f;
lightInCamSpace.x = 1.0 - lightInCamSpace.x;
lightInCamSpace.y = hcsPosition.y * 0.5f + 0.5;
lightInCamSpace.y = 1.0 - lightInCamSpace.y;
lightInCamSpace.z = camToLightVector.z;
fpParams->setNamedConstant("screenLightPos", lightInCamSpace);

You can make easy function "saturate" that transforms from coordinate space [-1, 1] to [0, 1].

Code: Select all

 Ogre::Vector3 saturate ( const Ogre::Vector3& point , const Ogre::Camera& cam)
{
     // Transform the 3D point into screen space
     Ogre::Vector3 result = camera.getProjectionMatrix() * (camera.getViewMatrix() *   
   point);

     // Transform from coordinate space [-1, 1] to [0, 1] and update in-value
     result.x = (result.x / 2) + 0.5f;
     result.y = 1 - ((result.y / 2) + 0.5f);
     return result;
}

GlobalExplorer · Post by **GlobalExplorer** » Thu May 01, 2008 12:27 pm

depositfiles sucks ass!!

Post by **jacmoe** » Thu Dec 18, 2008 10:10 pm

Seems like we lost it.

I'd be a happy coder if someone would be so kind and upload it!

Lexx · Post by **Lexx** » Fri Dec 19, 2008 12:18 am

Hi there, I'm here \o/
fcking depositfiles.com...

there's new links:
source: http://www.sendspace.com/file/5v7ubz
demo: http://www.sendspace.com/file/2nqfsm

duh... looks like sendspace is another <sensored> service...

source: http://www.savefile.com/files/1937851
demo: http://www.savefile.com/files/1937855

Post by **jacmoe** » Fri Dec 19, 2008 12:51 am

Cool! Thanks a lot!

xadhoom · Post by **xadhoom** » Fri Dec 19, 2008 11:38 am

I recommend this server: http://www.mediafire.com/

Its as easy as it should and (currently) reliable...

mapleleaf · Post by **mapleleaf** » Fri Aug 21, 2009 3:40 am

I can't download because is not connected to the download link.

Please repair...........

boyamer · Post by **boyamer** » Fri Aug 21, 2009 9:26 am

Me too,anyone can provide a working link please?

Lexx · Post by **Lexx** » Sun Aug 30, 2009 9:44 am

new link:
http://www.mediafire.com/?xgtwnjdmx2g

chenxiaobang3 · Post by **chenxiaobang3** » Sun Aug 30, 2009 12:42 pm

I can't download either.

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Volumetric lightshafts via GPU

Volumetric lightshafts via GPU

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