OgreDecal: A mesh-based decal generator

[fd9_]

[youtube]IPpY8v5-8kE[/youtube]

Frustrated by the lack of any built-in mesh decal generator for Ogre3D, I decided to go through the painstaking process of making one myself, which actually didn't turn out to be too bad. It's more or less based on the approach described here: http://blog.wolfire.com/2009/06/how-to-project-decals/

It's not perfect, but works well enough in most of the simple test cases I've tried. If there is enough interest, I'll clean it up a little bit and release the source.

Update 9/28:
The source is now available on github. I've posted all of the links and information on the wiki

[bstone]

Looks good, but you should definitely notch the depth bias a bit on the decal materials to fix that z-fight flicker.

[fd9_]

Looks good, but you should definitely notch the depth bias a bit on the decal materials to fix that z-fight flicker.

Thanks, I added depth_bias and it looks much better now.

[amigoface]

It's not perfect, but works well enough in most of the simple test cases I've tried. If there is enough interest, I'll clean it up a little bit and release the source.

definitively yes !!!, please

[Rambus]

Very nice

I would also like to peak at the source.

[Alexiss]

Wow, that would be awesome. Kudos for your work

[Pulas]

Very interesting! I am waiting for the source release...

[duststorm]

Great work! This is a very nifty feature to have on hand when you need it.
You should definitely release it!

[Zonder]

Yeah great work. This is something on my list to look into so I would be interested in the source as well

[Slappy]

It looks amazing, kudos for you!

[TheSHEEEP]

Hmm... do we have a decals sample yet?...

[Xavyiy]

Congrats, looks really nice!

+1 for the source release! Also, it would be interesting to officially intergate it into the Ogre core.

With some precautions in the implementation: make it compatible with static geometry, maybe even with "animated models"(updating the decal geometry when needed), etc it could be really useful for almost all people using Ogre.

Xavier

[fd9_]

Wow, thanks everyone for the encouraging feedback! I'll work on getting a release out soon (there are still a couple things left I need to do). I have no plans for supporting animated geometry - I'll let someone else tackle that.

[Treon]

looks really nice, it indeed would be interesting to officially intergate it into Ogre.

[syedhs]

Wow, thanks everyone for the encouraging feedback! I'll work on getting a release out soon (there are still a couple things left I need to do). I have no plans for supporting animated geometry - I'll let someone else tackle that.

Release early, release often

[jacmoe]

I really want to have my grubby paws on some source code!

I have no plans for supporting animated geometry - I'll let someone else tackle that.

Just whack it into a Bitbucket repository, and let people tackle it.

[AshMcConnell]

Cool stuff, great work!

Could this be used for "blob" shadows?

[nevarim]

seems great this project

[duststorm]

Could this be used for "blob" shadows?

I believe so.
fd9_, do you have an idea of the performance of the decals?

[fd9_]

Could this be used for "blob" shadows?

I believe so.
fd9_, do you have an idea of the performance of the decals?

Well, there are two different categories: the performance of the calculation itself and then the rendering cost.

The calculation is going to be dependent on the size of the decal and the amount of triangles in the scene. You start out with an AABB and calculate all the triangles in the scene that intersect it. For simplicity, my world is a single mesh which I test against, and I ignore any other objects. Right now I'm using Bullet to perform the AABB-triangle and clipping tests, but I plan to separate that code out so the algorithm is independent of any physics engine. Since the world can potentially be very large, I'll most likely provide some sort of optional callback function (i.e, GetTrianglesInAABB), so that the end-user can make use of any optimizations provided by whichever physics engine they may end up using. By default, the algorithm will just use a brute-force test.

I'm currently using an indexed triangle list for the rendering operation with a single begin()/end(), and I seem to be getting an average of 6 batches per decal. Now I don't really know how Ogre optimizes this stuff internally, but my understanding was that if you have a single object with a single material, you should be able to render it in one batch. I've tried using one scene node per decal, and I've tried using a single global scene node for every decal, but it doesn't seem to make any difference. I know Ogre has a static geometry feature, but I haven't tried using that yet. My initial thought was that perhaps I needed a triangle strip to get it down to 1 batch, but from my reading so far, it seems that an indexed triangle list should be just as fast. Perhaps someone can clarify this, since this is not my area of expertise. Isn't it possible to somehow have all decals of the same material rendered in the same batch as well?

About the shadow blob: I don't see why it wouldn't work, if optimized correctly.

[bstone]

As long as there's one begin()/end() section of the ManualObject per decal you should be getting one batch per decal as well. If you have materials with multiple passes (e.g. per light) then you will see the related increase in the batch counts.

[fd9_]

As long as there's one begin()/end() section of the ManualObject per decal you should be getting one batch per decal as well. If you have materials with multiple passes (e.g. per light) then you will see the related increase in the batch counts.

There is only one begin()/end() sequence and my material is set up like this:

Code: Select all

 material SmileyFace
 {
   technique
   {
     pass
     {
         alpha_rejection greater_equal 128
         lighting on
         depth_write on
         depth_bias 4

         
         texture_unit
			{
				texture SmileyFace.png
			}
       
     }
   }
 }
 

[fd9_]

I've spent the last week or so cleaning up the source code (as best I could) and provided a wealth of information on the wiki. Please read the wiki before using it, especially the last part. Let me know how it goes.

Go to the wiki!

[nevarim]

great work fd9

would be nice if there was a part that explains how to use a decal on the ground as a pointer (there are no so many info on this part on forum and are all old )

thankss

Nevarim

[fd9_]

great work fd9

would be nice if there was a part that explains how to use a decal on the ground as a pointer (there are no so many info on this part on forum and are all old )

thankss

Nevarim

You mean like this?

[youtube]5PwggRRPHIM[/youtube]

All you need to do is cast a ray into the scene and create a new decal each frame. You can use this class to cast the ray: http://www.ogre3d.org/docs/api/html/cla ... Query.html

Does that help?