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

# 创建窗口
def CreateWindow():
    global window
    # pass arguments to init
    glutInit(sys.argv)
    
    # Select type of Display mode:
    #  Double buffer，# 注意这里开了双缓存：绘制后必须调用glutSwapBuffers()，才能看到绘制结果
    #  RGBA color
    # Alpha components supported
    # Depth buffer
    glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE | GLUT_DEPTH) 
     
    # get a 640 x 480 window
    glutInitWindowSize(640, 480)
    
    # the window starts at the upper left corner of the screen
    glutInitWindowPosition(0, 0)
    
    # Okay, like the C version we retain the window id to use when closing, but for those of you new
    # to Python (like myself), remember this assignment would make the variable local and not global
    # if it weren't for the global declaration at the start of main.
    window = glutCreateWindow("Realistic Reflection by RISC")

# 初始化OpenGL参数
def InitGL(Width, Height):                # We call this right after our OpenGL window is created.
    # 设置背景色，很好看的蓝色
    glClearColor(0.2, 0.5, 1.0, 1.0)
    glClearDepth(1.0)                    # Enables Clearing Of The Depth Buffer
    glClearStencil(0)
    glDepthFunc(GL_LEQUAL)                # The Type Of Depth Test To Do
    glEnable(GL_DEPTH_TEST)                # Enables Depth Testing
    glShadeModel(GL_SMOOTH)                # Enables Smooth Color Shading
    
    glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST)
    glEnable(GL_TEXTURE_2D)
    
    glMatrixMode(GL_PROJECTION)
    # Reset The Projection Matrix
    glLoadIdentity()
    # Calculate The Aspect Ratio Of The Window
    gluPerspective(45.0, float(Width)/float(Height), 0.1, 100.0)
    
    glMatrixMode(GL_MODELVIEW)
    glLoadIdentity()

# 封装func函数，在执行func函数前后清理缓存和缓存切换
def wrapedDrawObject(func):
    # 清理深度和颜色缓存
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT|GL_STENCIL_BUFFER_BIT)
    # 重置视角
    glLoadIdentity()
    # 执行绘制函数
    func()
    # 切换缓存
    glutSwapBuffers()

# 以指定func函数为核心渲染函数
def run(func):
    CreateWindow()
    # 封装绘制函数（偏函数）
    from functools import partial
    drawObject = partial(wrapedDrawObject, func)
    # 窗口显示时候，就绘制图
    glutDisplayFunc(drawObject) 
    # 程序空闲时候，就绘制图(一直空闲就一直不停的画)
    glutIdleFunc(drawObject)
    # 初始化OpenGL
    InitGL(640, 480)
    # 开始事件处理循环
    glutMainLoop()

# 调用示例
# 绘制函数示例（无需切换缓存，重置视角）
def drawObject():
    # 移动位置
    glTranslatef(0.0, 0.0, -2.0)
    # 绘制三角形
    glBegin(GL_POLYGON)
    glVertex3f(0.0, 1.0, 0.0)
    glVertex3f(1.0, -1.0, 0.0)
    glVertex3f(-1.0, -1.0, 0.0)
    glEnd()

# 执行绘制函数
run(drawObject)