Python 3学习笔记（14）：PyOpenGL之绘制螺帽

• 目的

1、建立光照模型

2、绘制螺帽，可用箭头键切换视角。

• 内容 

选定投影方式后，下一步就是选择螺钉视图的光照模型。渲染环境包括光照和材料属性（金属光泽），唯一的光源在观察者的左上方。

螺钉的螺帽部分有六个光滑的侧面，其顶部和底部也是光滑的。我们可以用两个六边形（代表顶部和底部）和围绕其边缘的一系列矩形（代表各个侧面）来构造这个实心对象。

我们使用GL_TRIANGLE_FAN来绘制它。我们使用六个三角形组成的三角形扇面来表示螺帽的顶部和底部。画螺帽共需要18个图元，顶部和底部各由6个三角形组成，6个矩形则组成螺帽的侧面。

坐标系的原点定义在螺帽的中心。 

• 代码 

 

#coding:utf-8

import sys
from math import pi as PI
from math import sin, cos
from math import sqrt

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

#将指定为三个坐标组的法线向量换算。
def ReduceToUnit(vector): 
	# Calculate the length of the vector		
	length = sqrt((vector[0]*vector[0]) + (vector[1]*vector[1]) +(vector[2]*vector[2]));
	#Keep the program from blowing up by providing an exceptable
	#value for vectors that may calculated too close to zero.
	if (length == 0.0):
		length = 1.0 
	#Dividing each element by the length will result in a	unit normal vector.
	vector[0] /= length 
	vector[1] /= length 
	vector[2] /= length 
 
# Points p1, p2, & p3 specified in counter clock-wise order
# float v[3][3], float out[3]
def calcNormal(v,out): 
	#float v1[3],v2[3];
	v1=[0.0 for i in range(3)]
	v2=[0.0 for i in range(3)]
	out=[0.0 for i in range(3)]	
	xx = 0 
	yy = 1 
	zz = 2 

	# Calculate two vectors from the three points
	v1[xx] = v[0][xx] - v[1][xx] 
	v1[yy] = v[0][yy] - v[1][yy] 
	v1[zz] = v[0][zz] - v[1][zz] 

	v2[xx] = v[1][xx] - v[2][xx] 
	v2[yy] = v[1][yy] - v[2][yy] 
	v2[zz] = v[1][zz] - v[2][zz] 

	# Take the cross product of the two vectors to get
	# the normal vector which will be stored in out
	out[xx] = v1[yy]*v2[zz] - v1[zz]*v2[yy] 
	out[yy] = v1[zz]*v2[xx] - v1[xx]*v2[zz] 
	out[zz] = v1[xx]*v2[yy] - v1[yy]*v2[xx] 

	# Normalize the vector (shorten length to one)
	ReduceToUnit(out) 

def RenderHead():
	global x,y,angle	# Calculated positions
	height = 25.0		# Thickness of the head
	diameter = 30.0		# Diameter of the head
	#float normal[3],corners[4][3];    // Storeage of vertices and normals
	corners = [[0.0 for i in range(3)] for i in range(4)]
	normal=[0.0 for i in range(3)]
	step = (PI/3.0)     # step = 1/6th of a circle = hexagon
    
	# Set material color for head of bolt
	glColor3f(0.0, 0.0, 0.7) 

    # ----------开始一个三角形扇面覆盖 螺帽顶面------
	glFrontFace(GL_CCW)
	glBegin(GL_TRIANGLE_FAN)
	#All the normals for the top of the bolt point straight up the z axis.
	glNormal3f(0.0, 0.0, 1.0)
	# Center of fan is at the origin
	glVertex3f(0.0, 0.0, height/2.0)

	#把圆圈分成6个部分，然后开始下降点来绘制扇面.  避免使用glFrontFace()进行状态改变
	# 第一个和最后一个顶点封闭扇面
	glVertex3f(0.0, diameter, height/2.0)

	angle=(2.0*PI)-step
	while angle>0 :
		#Calculate x and y position of the next vertex
		x = diameter* sin(angle)
		y = diameter* cos(angle)       
		# Specify the next vertex for the triangle fan
		glVertex3f(x, y, height/2.0)
		angle-=step

	# Last vertex closes the fan
	glVertex3f(0.0, diameter, height/2.0)
	glEnd()

    # ---------开始一个三角形扇面覆盖 螺帽底面--------
	glBegin(GL_TRIANGLE_FAN)

	glNormal3f(0.0, 0.0, -1.0)       
	# Center of fan is at the origin
	glVertex3f(0.0, 0.0, -height/2.0)

	angle=0
	while angle<(2.0*PI)-step :
		#Calculate x and y position of the next vertex
		x = diameter* sin(angle)
		y = diameter* cos(angle)       
		# Specify the next vertex for the triangle fan
		glVertex3f(x, y, -height/2.0)
		angle+=step

	# Last vertex closes the fan
	glVertex3f(0.0, diameter, -height/2.0)
	glEnd()

    # ---------开始一个四角形覆盖 螺帽侧面
	glBegin(GL_QUADS);
	angle=0
	while angle<(2.0*PI)-step :
		x = diameter* sin(angle)
		y = diameter* cos(angle)              
		#start at bottom of head
		corners[0][0] = x
		corners[0][1] = y
		corners[0][2] = -height/2.0

		#extrude to top of head
		corners[1][0] = x
		corners[1][1] = y
		corners[1][2] = height/2.0

		#Calculate the next hex point
		x = diameter* sin(angle+step) 
		y = diameter* cos(angle+step) 

		#Make sure we aren't done before proceeding
		if (angle+step < 3.1415*2.0):
			#If we are done, just close the fan at a  known coordinate.
			corners[2][0] = x
			corners[2][1] = y
			corners[2][2] = height/2.0

			corners[3][0] = x
			corners[3][1] = y 
			corners[3][2] = -height/2.0 
		else:
			corners[2][0] = 0.0 
			corners[2][1] = diameter 
			corners[2][2] = height/2.0 

			corners[3][0] = 0.0 
			corners[3][1] = diameter 
			corners[3][2] = -height/2.0 

		calcNormal(corners, normal) 
		glNormal3fv(normal) 
        
		glVertex3fv(corners[0])
		glVertex3fv(corners[1])
		glVertex3fv(corners[2])
		glVertex3fv(corners[3])
		angle+=step
				
	glEnd() 



def RenderScene():
	global xRot,yRot
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)					

	# Save the matrix state
	glMatrixMode(GL_MODELVIEW) 
	glPushMatrix() 
    # 绕X轴和Y轴旋转(角度,x,y,z)
	glRotatef(xRot, 1.0, 0.0, 0.0)
	glRotatef(yRot, 0.0, 0.0, 1.0)	
	# Render just the hexagonial head of the nut
	RenderHead()
	glPopMatrix()
    #双缓冲的刷新模式； Swap buffers
	glutSwapBuffers()					

#设置渲染状态
def SetupRC():	
	# Light values and coordinates光照 值与坐标；环境光，漫射光，镜面光，光的坐标,
	ambientLight = [0.4, 0.4, 0.4, 1.0 ]
	diffuseLight = [0.7, 0.7, 0.7, 1.0 ]
	specular = [ 0.9, 0.9, 0.9, 1.0]
	lightPos = [ -50.0, 200.0, 200.0, 1.0]
	specref =  [ 0.6, 0.6, 0.6, 1.0]


	glEnable(GL_DEPTH_TEST)	# Hidden surface removal
	glEnable(GL_CULL_FACE)	# Do not calculate inside of solid object
	glFrontFace(GL_CCW) 
	
	glEnable(GL_LIGHTING) 

	# Setup light 0
	glLightModelfv(GL_LIGHT_MODEL_AMBIENT,ambientLight) 
	glLightfv(GL_LIGHT0,GL_AMBIENT,ambientLight) 
	glLightfv(GL_LIGHT0,GL_DIFFUSE,diffuseLight) 
	glLightfv(GL_LIGHT0,GL_SPECULAR,specular) 

	# Position and turn on the light
	glLightfv(GL_LIGHT0,GL_POSITION,lightPos) 
	glEnable(GL_LIGHT0) 

	# Enable color tracking
	glEnable(GL_COLOR_MATERIAL) 
	
	# Set Material properties to follow glColor values
	glColorMaterial(GL_FRONT, GL_AMBIENT_AND_DIFFUSE) 

	# All materials hereafter have full specular reflectivity with a moderate shine
	glMaterialfv(GL_FRONT, GL_SPECULAR,specref) 
	glMateriali(GL_FRONT,GL_SHININESS,64) 
	
	glClearColor(0.0, 0.0, 0.0, 1.0)  #背景黑色
	

#改变窗口大小时调用
def ChangeSize(w,h):
	nRange = 100.0
	if(h == 0):     #防止除数为0
		h = 1
	glViewport(0, 0, w, h)						#设置视区大小
	glMatrixMode(GL_PROJECTION)					#投影矩阵模式
	glLoadIdentity()							#矩阵堆栈清空
	#设置裁剪窗口大小
	if (w <= h): 
		glOrtho (-nRange, nRange, -nRange*h/w, nRange*h/w, -nRange*2.0, nRange*2.0)	
	else: 
		glOrtho (-nRange*w/h, nRange*w/h, -nRange, nRange, -nRange*2.0, nRange*2.0)	
						
	glMatrixMode(GL_MODELVIEW)					#模型矩阵模式
	glLoadIdentity()

def SpecialKeys(key,x,y):
	global xRot,yRot
	if(key == GLUT_KEY_UP):
		xRot-= 5.0
	if(key == GLUT_KEY_DOWN):
		xRot += 5.0
	if(key == GLUT_KEY_LEFT):
		yRot -= 5.0
	if(key == GLUT_KEY_RIGHT):
		yRot += 5.0
	if(key > 356.0):
		xRot = 0.0
	if(key < -1.0):
		xRot = 355.0
	if(key > 356.0):
		yRot = 0.0
	if(key < -1.0):
		yRot = 355.0
	glutPostRedisplay()

xRot=0.0
yRot=0.0
print("三维螺帽，按箭头键改变视角！")
#使用glut初始化OpenGL
glutInit()
glutInitWindowSize(700,700)
#设置显示模式；（注意双缓冲）
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB| GLUT_DEPTH)
glutCreateWindow("Bolt Head")

glutReshapeFunc(ChangeSize)
glutSpecialFunc(SpecialKeys)     #注册键盘回调函数
#调用函数绘制图像
glutDisplayFunc(RenderScene)
SetupRC()
#主循环
glutMainLoop()