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書名： Panda3d 1.7 Game Developer's Cookbook
作者名： Christoph Lang
本章字數： 358字
更新時間： 2021-04-09 21:21:47

Making objects follow a predefined path

In this recipe we will see how to move a model along a line, typically referred to as a path, stored in Panda3D's model format. This can come in very handy for setting paths of non-player characters inside a level. Another common use of this is to attach the camera to a path and make it fly through the game world smoothly.

Getting ready

To follow this recipe you first have to set up a project as described in Setting up the game structure. In addition, you need to create a curve in Maya or Blender and export it to Panda3D's .egg file format. In case you don't have these tools or do not know how to work with them, here's a sample curve you can paste into a text editor and save it as path.egg:

<CoordinateSystem> { Z-up }
<Group> Curve {
  <VertexPool> Curve {
    <Vertex> 0 {
      -2.66117048264 -0.964361846447 0.0 1.0
    }
    <Vertex> 1 {
      1.8930850029 -0.948404431343 0.0 1.0
    }
    <Vertex> 2 {
      10.3484048843 1.0 0.0 1.0
    }
    <Vertex> 3 {
      -3.6957449913 0.0 0.0 1.0
    }
  }
  <NURBSCurve> {
    <Order> { 4 }
    <Knots> { 0.0 0.0 0.0 0.0 1.0 1.0 1.0 1.0 }
    <VertexRef> { 0 1 2 3  <Ref> { Curve }}
  }
}

How to do it...

Making objects follow a predefined path can be done like the following:

Copy the file containing the curve to the models directory of your project and make sure it is named path.egg.

Copy the following code to Application.py:

from direct.showbase.ShowBase import ShowBase
from direct.actor.Actor import Actor
from direct.directutil.Mopath import Mopath
from direct.interval.IntervalGlobal import *

class Application(ShowBase):
    def __init__(self):
        ShowBase.__init__(self)

        self.smiley = self.loader.loadModel("smiley")
        self.smiley.reparentTo(render)

        self.mopath = Mopath()
        self.mopath.loadFile("path.egg")

        self.ival = MopathInterval(self.mopath, self.smiley, duration = 10)
        self.ival.loop()
        
        self.cam.setPos(0, -20, 0)

Press F6 to start the program. The smiley model will follow the path.

How it works...

All it takes for you to use predefined paths is to create a Mopath object and load the file containing the curve you want your object to follow. Then you pass the Mopath object to a MopathInterval that is responsible for interpolating the model position along the path over the specified duration. That's it—it's that easy!

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Panda3d 1.7 Game Developer's Cookbook

Making objects follow a predefined path

Getting ready

How to do it...

How it works...