Robot - simple hierarchical model

移動(Translate)や回転(Rotate)は拡大・縮小はインクリメンタルであるため、リセットしなければ変換用の行列に加算や乗算がどんどん加えられて行きます。土台、下腕、上腕を持つ簡単なロボットの例を、"OpenGL入門" エドワード・エンジェル著、滝沢徹・牧野祐子訳、ピアソン・エデュケーション刊を参考にして作ってみました。Cで書かれた部分的なサンプルコードをPythonに書き直すのは至って簡単でした。Translateの基本概念が前回分かったので、うんと楽です。ただ、変換の順番が問題になると、まだよく分かっていないことが露呈します。

Instance transformation is incremental. This is good for hierarchical instances with dependency on other objects in parent hierarchy. By refering a book "OpenGL, A PRIMER" by Edward Angel, I made a simple robot example using Python. "base" instance has a child instance "lower_arm" and "lower_arm" has a child instance "upper_arm". Translating C sample code to Python was very easy because I learned how the MODELVIEW matrix works.

In the following example, use key 'q', 'a', 'w', 's', 'e', 'd' to move each part of the robot.

import sys
import math
from OpenGL.GL import *
from OpenGL.GLU import *
from OpenGL.GLUT import *

BASE_RADIUS = 0.1
BASE_HEIGHT = 0.1
UPPER_ARM_WIDTH = 0.05
UPPER_ARM_HEIGHT=0.5
LOWER_ARM_WIDTH=0.08
LOWER_ARM_HEIGHT=0.3
tb=0
tl=45
tu=30

def display():
  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
  glMatrixMode(GL_MODELVIEW)

  glLoadIdentity()
  gluLookAt(2.0, 2.0, 2.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0)
  glColor3f(1.0, 0.0, 0.0)
  glRotatef(tb, 0.0, 1.0, 0.0)
  base()
  glTranslatef(0.0, BASE_HEIGHT, 0.0)
  glColor3f(0.0, 1.0, 0.0)
  glRotatef(tl, 0.0, 0.0, 1.0)
  lower_arm()
  glTranslatef(0.0, LOWER_ARM_HEIGHT, 0.0)
  glRotatef(tu, 0.0, 0.0, 1.0)
  glColor3f(0.0, 0.0, 1.0)
  upper_arm()
  glFlush()

def base():
  glPushMatrix()
  glRotatef(-90.0, 1.0, 0.0, 0.0)
  gluCylinder(p, BASE_RADIUS, BASE_RADIUS, BASE_HEIGHT, 10, 10)
  glPopMatrix()

def upper_arm():
  glPushMatrix()
  glTranslatef(0.0, 0.5*UPPER_ARM_HEIGHT, 0.0)
  glScalef(UPPER_ARM_WIDTH, UPPER_ARM_HEIGHT, UPPER_ARM_WIDTH)
  glutSolidCube(1.0)
  glPopMatrix()

def lower_arm():
  glPushMatrix()
  glTranslatef(0.0, 0.5*LOWER_ARM_HEIGHT, 0.0)
  glScalef(LOWER_ARM_WIDTH, LOWER_ARM_HEIGHT, LOWER_ARM_WIDTH)
  glutSolidCube(1.0)
  glPopMatrix()

def mykey(key, x, y):
  global tb, tl, tu
  if key=='q': # +base
    tb = tb + 5.0
  elif key=='a': # -base
    tb = tb - 5.0
  elif key=='w': #+lower
    tl = tl + 5.0
  elif key=='s': #-lower
    tl = tl - 5.0
  elif key=='e': #+upper
    tu = tu + 5.0
  elif key=='d': #-upper
    tu = tu - 5.0
  print "tb=", tb, " tl=", tl, " tu=", tu
  glutPostRedisplay()
    
glutInit( sys.argv )
glutInitDisplayMode( GLUT_SINGLE | GLUT_RGB )
glutInitWindowSize( 500, 500 )
glutInitWindowPosition(0,0)
glutCreateWindow( 'robot' )
glutDisplayFunc( display )
glutKeyboardFunc(mykey)
p=gluNewQuadric()
gluQuadricDrawStyle(p, GLU_LINE)

glClearColor(0.0, 0.0, 0.0, 0.0)

glMatrixMode(GL_PROJECTION)
glLoadIdentity()
gluPerspective(30, 1.0, 0.0, 100.0)

glutMainLoop()