Hi David, and thanks for the great explanation! It has been very helpful I will try to modify or instruct the import plugins of the file formats I need forcing the association between the maps and the texture unit meaning then.
Thanks again, Davide > > ---------- Forwarded message ---------- > From: David Spilling <david.spill...@gmail.com> > To: OpenSceneGraph Users <osg-users@lists.openscenegraph.org> > Date: Tue, 12 Jan 2010 12:35:34 +0000 > Subject: Re: [osg-users] 3d file formats supporting bump map > Hi Davide, > > Certainly the obj loader supports bump maps, but let me be clear about what > it actually does. Apologies if this comes over as patronising; I have no idea > of your level of expertise. > > In OSG/OpenGL land, textures (diffuse, bump map, specular map, etc.) are all > attached to a particular geometry via a texture ID - this is an integer index > ranging from 0 upwards. Shaders are then applied to this geometry that will > colour the pixel based on a particular understanding of what each texture ID > actually is. So for example, I can write a shader that assumes that texture > unit 0 is the diffuse colour, texture unit 1 is some sort of specularity map, > texture unit 2 is a bump map, etc. Or I can assume (for example as osgShadow > tends to) that texture unit 0 is the diffuser colour, texture unit 1 is the > shadow map. > > However - and this is the key - there is nothing that enforces this mapping > between texture unit and "meaning". > > 3DS, and the obj format, both explicitly include entries in the model for > "diffuse texture" and "specular map" and "bump map" and so on. However the > 3DS or obj format loader doesn't know what shader you are going to apply to > this model, so has no idea which texture ID/unit to assign a loaded "bump > map" texture to. Should it be 1? 2? etc. > > Some formats (e.g. .osg) allow you to save an objects shader within the > object definition itself, thereby guaranteeing that the textures that the > object loads are assigned to the right texture unit, and used in the right > way. 3DS and .obj don't. > > AFAIK, there is currently no OSG-wide method for enforcing any consistency. > > All that being said, the OBJ loader allows you to specify what texture units > you want which maps to go to when you load the model, via an options string. > The options are all listed in the first few lines of ReaderWriterOBJ.cpp. The > mapping between the flags in the .obj file and the name of the texture is in > lines 434 onwards of obj.cpp. (It's useful to have a look at that, because > the OBJ spec is not rigourously followed by all modelling tools - e.g. you > see map_opacity in some obj files, even though it should be map_d according > to the spec). > > I'm not amazingly familiar with osgFX, but reading the source for the > BumpMapping technique, I notice that > a) you can define which texture units should be used for diffuse and normal > (note : not bump) textures, and > b) by default these are 0=normal, 1=diffuse. > > I also don't know what Blender exports in terms of maps. When you say that > the blender export isn't exporting the bump map, have you looked in the OBJ > file to actually see whether there is a "map_bump" (or "map_Bump", or just > "bump") in it? Has it been called something else by the exporter? > > Hope that helps, > > David > > > _______________________________________________ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
