Collision on dynamic ground

Gruik1 · December 13, 2007, 1:06pm

Hi,

I have some problem picking my heightfield.

I create a world from a greyscale heightmap. The heightfield i get is 1 Geom containing GeomTriangles (i don’t use .egg 'cos my heightfield is fully dynamic and if find it easier this way).

So everything’s good : I have an heightfield on the screen (and objects placed on it at the good height.)
But now i want to click on my heightfield and retrieve the good coords. So i have to be able to pick my heightfield. So I need a ColisionSolid.

I saw on the forum that lots of people tag their .egg so that they have it automaticaly but that doesn’t work for my kind of heightfield.
I kept looking and find this in the API : CollisionFloorMesh. I saw you give it vertices and triangles and it’s good.
PROBLEM : it seems it’s not in Panda anymore!

So I think I’ll have to create CollisionPolygon for each triangle of my GeomTriangles but I find it really heavy.

Does anyone have an idea that could help me ? Or at least a way to create a CollisionSolid from a Geom automaticaly ?

Thanks a lot
Gruik

rdb · December 13, 2007, 4:52pm

ynjh_jo wrote a function to convert normal geometry to collisiongeometry (see this thread).

ynjh_jo:

to convert Geom into CollisionPolygons, you need to do :

create CollisionNode
for every triangle, create a CollisionPolygon and add it to the CollisionNode

taken from my polygonal button :
discourse.panda3d.org/viewtopic.php?p=15762

  def convertGeom2CollPoly(self):
      geomParent=self.geom.getParent()
      cn=CollisionNode('CN-'+self.geom.getName())
      self.collNP=geomParent.attachNewNode(cn)

      collGeom=self.geom.copyTo(geomParent)
      collGeom.setTransform(self.geom.getTransform())
      collGeom.flattenStrong()

      collNumVtx=0
      collVertices=[]
      geom=collGeom.node().getGeom(0)
      collVtxData=geom.getVertexData()
      numVtx=collVtxData.getNumRows()
      # create vertex reader
      collvtxreader=GeomVertexReader(collVtxData)
      # set the start position for reading the vertices,
      # begin reading at column 0, which is vertex position
      collvtxreader.setColumn(0)
      for prim in range(geom.getNumPrimitives()):
          # decompose high-order primitive
          collFaceData=geom.getPrimitive(prim).decompose()
          for i in range(0,collFaceData.getNumFaces()*3,3):
              collvtxreader.setRow( collFaceData.getVertex(i) )
              vtx1=collvtxreader.getData3f()
              collvtxreader.setRow( collFaceData.getVertex(i+1) )
              vtx2=collvtxreader.getData3f()
              collvtxreader.setRow( collFaceData.getVertex(i+2) )
              vtx3=collvtxreader.getData3f()
              cn.addSolid( CollisionPolygon(vtx1,vtx2,vtx3) )
      # remove the temporary Geom
      collGeom.removeNode()
      # put the collision node to be the visible geometry's child
      self.collNP.wrtReparentTo(self.geom)

In there, I simply make a copy of the geom and flatten the transform, since I don’t need any fancy structure for buttons.

PS : I haven’t tried v1.4.1 yet

Gruik1 · December 13, 2007, 5:00pm

Thanks it certainly will help!

I did approximatively the same thing this afternoon (in fact it doesn’t take so much time to compute, even for a big heightfield) but just for GeomTriangles. So this generic one will make be better!

Thanks again
Gruik

Josh_Yelon · December 13, 2007, 5:38pm

I should mention that checking the heightfield directly should be much faster than converting to polygons and then checking collision against the polygons.

rdb · December 13, 2007, 6:12pm

Yes, in the next version of PGMM I hope to have an automatic collisiongeometry-generator built-in.

Gruik1 · December 13, 2007, 6:27pm

The problem here is that, in order to check the heightfield, I have to project my mouse position on the heightfield to have a x,y coord and then the height of the point … So the only way I see is this one which gives me the 3 coords at the same time.
Do you have an idea about how you would do ?