HI Christian, The way to use a mask like this would be to read an osg::Image and read from it directly. There is no reason to require the use Texture2D - this is only required if you want to do operations down on the GPU. osg::Image does have access methods for getting individual pixels.
However, the way I'd tackle this problem would be by providing boundary polygons which are then tessellated to provide a triangular mesh that acts to describe the forest coverage. One would then compute the area for each of these triangles and then have a map of accumulated area to index position into the triangle list. This would give us the ability to have a random value map to a particular triangle, one then can use two more random values to provide the baricentric coords within than triangle and form this to the final XY location. From the XY location you then intersect the terrain and place the tree. A variation on this would be use the a subset of the actual terrain mesh, as this would then avoid the need for doing the intersection test as you'd get the correct XYZ location. The boundaries of the terrain triangles would might also be something that you'd want to manage to avoid an artificial look, this could be done by trimming a copy of the terrain triangles of interest by the polygonal boundary. A further variation on this would be to add probability weights to the vertices of the coverage mesh so you can change the density of trees across the model, one also could through in tree type variation at the same time. All of this is well outside the scope of the osgforest example though, but hopefully should give you a few ideas. Robert. On Sat, Feb 28, 2009 at 12:24 AM, Christian Sam <[email protected]> wrote: > hi, > > i would like to extend the example-program "osgforest" in a way so that the > placement of trees becomes user-controllable via an additional raster mask. > in detail: a 1bit rasterfile should mark treeless areas with a value of "0" > and tree-covered areas with a value of "1". subsequent this mandatory > partitioning, i would like use the existing, random placement of trees in > tree-covered areas. > > i'm new to osg, so i have a few questions about how to implement this, and > would also be happy to get some clues from you. > > > * can i use a simple osg::texture2D (nearest neighbour worldcoordinate scaled > to osgforest's terrain extent), as raster mask? > > * if yes, how can i query/access a raster value at a specific texture > coordinate? > > * how can i prevent that the raster mask will be rendered in the final scene? > (would a nodemask be the right way, or are there any better/simpler ways?) > > * in this first approach i will only implement 2 different tree regions: > covered and non-covered. my plan is to extend to the existing > "createTreeList" function with a simple check for the raster mask value at > the randomly generated tree position coordinates. only if it happens to lie > inside a tree-covered area, the tree will be pushed into the trees list. > maybe someone knows a more elegant way? > > > best regards, > christian > > ------------------ > Read this topic online here: > http://forum.openscenegraph.org/viewtopic.php?p=7664#7664 > > > > > > _______________________________________________ > osg-users mailing list > [email protected] > http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org > _______________________________________________ osg-users mailing list [email protected] http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
