[PyOpenGL-Users] recommendation for setting correctly the new direction of an object

[Roland E. <r.e...@gm...>]

Hi,

I am currently writing a third person view space shooter where the 
player can freely fly in the "map". I want to define an arcade flying 
model like in most space shooter or spaceship simulation, but I face the 
problem of specifying the transformation right.

For the moment, my scene contains the player space ship pointing toward 
the negative z axis, with the camera a little bit behind it. In front of 
the ship there are 2 objects. When I apply some thrust to the player 
spaceship it goes forward, but if I turn the ship, it is not changing 
direction, while the ship and the camera are turning.

My questions are the following:

1. Given the code below, why have I to call the method 
self.__chasingView() after rendering the player's ship?

2. How to change the direction of the ship? Am I missing some glRotate() 
functions somewhere in the code or should I change the code of method 
setNewPosition() in such a way that the position of the ship is computed 
on all 3 axis?

Below is the main code rendering the scene:

         glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
         glLoadIdentity(); # /* clear the matrix */
         playerShipPos = self.__player.getPosition()
         x, y, z = self.__player.getAngle()
         self.__lightVP.switchOn()
         glTranslate(0.0, -3.0, -20.0)
         glRotate(10.0, 1.0, 0.0, 0.0)
         self.__player.render()
         self.__chasingView(playerShipPos[0], playerShipPos[1], 
playerShipPos[2], x, y, z)

         for entity in self.__entities:
             self.__updateRadar(entity)
             glPushMatrix()
             entity.render()
             glPopMatrix()

         glFlush ()

- Method render() for both self.__player and entity is:

         glPolygonMode(GL_FRONT_AND_BACK, GL_FILL)

         #Load vertex List and Normals List
         self.vbo_vert.bind()
         glEnableClientState(GL_VERTEX_ARRAY)
         glVertexPointerf(self.vbo_vert) # Specify the vertex list to be 
used to draw the model
         self.vbo_vert.unbind()
         self.vbo_norm.bind()
         glEnableClientState(GL_NORMAL_ARRAY)
         glNormalPointerf(self.vbo_norm) # Specify the normal list to be 
used to draw the model
         self.vbo_norm.unbind()

         # Activate face culling
         glEnable(GL_CULL_FACE)
         glCullFace(GL_BACK)
         # Apply transformation
         if not(self.isPlayer):
             glTranslate(*self.position)
             glRotatef (self.x_angle, 1.0, 0.0, 0.0);
             glRotatef (self.y_angle, 0.0, 1.0, 0.0);
             glRotatef (self.z_angle, 0.0, 0.0, 1.0);

         start_pos = 0
         # In For .. Loop
         for obj in self.modelData:
             # Set Object Material
             glMaterialfv(GL_FRONT, GL_SPECULAR, obj.matdata.specular)
             glMaterialfv(GL_FRONT, GL_SHININESS, obj.matdata.specularCoeff)
             glMaterialfv(GL_FRONT, GL_AMBIENT, obj.matdata.ambient)
             glMaterialfv(GL_FRONT, GL_DIFFUSE, obj.matdata.diffuse)
             # Draw object
             glDrawArrays(GL_TRIANGLES, start_pos, obj.nbrVertices)
             start_pos += obj.nbrVertices

         glDisableClientState(GL_VERTEX_ARRAY)
         glDisableClientState(GL_NORMAL_ARRAY)
         # vbo class usage


The function I use to set the new location of the ship based on the 
current thrust is:

     def setNewPosition(self):
         self.addToPosition(z=-(self.thrust * self.tick))

The above method is called in the main loop before the rendering of the 
scene.

The self.__chasingView() method is:

     def __chasingView(self, planex, planey, planez, pitch, heading, roll):

         glRotatef(roll, 0.0, 0.0, 1.0)
         glRotatef(heading, 0.0, 1.0, 0.0)
         glRotatef(pitch, 1.0, 0.0, 0.0)
         glTranslate(-planex, -planey, -planez)

That code comes from the opengl programmer's guide with a few changes to 
adapt to the fact that the player's ship is looking down the negative Z 
axis.


Hope this lengthy email doesn't break any rules of this mailing list.


Thanks for your help,


Roland.