Creating objects "on the fly"

[Pedro]

Hi everyone !

I’d like to know if there is a way of creating objects on the fly. I have method which computes the object vertex position and an other one which computes the faces of the object. I could create an egg file (although all my attempts to create a model with a egg, even a really simple model have failed - I think I did not get how it works) but I have a lot of objects, and writing into a file then loading them seems a bit slow.

What I would like to do is to create the object directly from my program. Is this possible ?

[enn0x]

Yes, it is possible. There is a full section of the manual dedicated to this topic: “Procedurally Generating 3D Models”.

Or you can use the egg library and then directly load a NodePath from the egg data without writing the data to a file by using loadEggData( eggData ).

enn0x

[Pedro]

Thanks, I’m going to take a look at it.

[Pedro]

I tried this after reading the manual, but nothing shows up on screen. Any idea ?

import direct.directbase.DirectStart
from direct.showbase import DirectObject
from pandac.PandaModules import *

class Test(DirectObject.DirectObject):

def __init__(self):
    self.create()
    run()

def create(self):
    array = GeomVertexArrayFormat()
    array.addColumn(InternalName.make('vertex'), 3, Geom.NTFloat32, Geom.CPoint)

    format = GeomVertexFormat()
    format.addArray(array)
    format = GeomVertexFormat.registerFormat(format)

    vdata = GeomVertexData('name', format, Geom.UHStatic)

    vertex = GeomVertexWriter(vdata, 'vertex')

    vertex.addData3f(1, 0, 0)
    vertex.addData3f(1, 1, 0)
    vertex.addData3f(0, 1, 0)
    vertex.addData3f(0, 0, 0)
    
    prim = GeomTriangles(Geom.UHStatic)

    prim.addVertex(0)
    prim.addVertex(1)
    prim.addVertex(2)
    prim.closePrimitive()

    prim.addVertex(2)
    prim.addVertex(1)
    prim.addVertex(3)
    prim.closePrimitive()
    
    geom = Geom(vdata)
    geom.addPrimitive(prim)

    node = GeomNode('gnode')
    node.addGeom(geom)

    nodePath = render.attachNewNode(node)
    nodePath.setColor(1,0,0,1)
    nodePath.setPos(0,-5,0)

t = Test()

[rdb]

It works fine for me. You just have to reposition the camera a bit to see it. Drag with the right mouse a bit upwards to zoom out, then drag the middle mouse button around to rotate. You will see two perfect red triangles.

[enn0x]

Yes, it works for me too.

This is your first triangle, visible only from “above”:

  2----1
   \   |
    \  |
     \ |
      \|
  3    0

And this your second, visible only from “below”:

  2----1
  |   / 
  |  /  
  | /   
  |/    
  3    0

But I assume you wanted to do something like this:

  2----1
  |\   |
  | \  |
  |  \ |
  |   \|
  3----0

You have to create the triangle indices in counter-clockwise order, like this:

  prim.addVertex(0)
  prim.addVertex(1)
  prim.addVertex(2)
  prim.closePrimitive()

  prim.addVertex(0)
  prim.addVertex(2)
  prim.addVertex(3)
  prim.closePrimitive()

enn0x

[ynjh_jo]

yep, addition :
your node is behind your camera
if it’s still hard to see, use nodePath.showBounds()

[Pedro]

Sorry guys. I didn’t even thought that the camera position might be the problem. I must have been tired last friday…

Thanks anyway !