在pyOpenGL中绘制简单的正方形

Question

我正在自学OpenGL，使用的是pyopengl，现在遇到一个问题，想要渲染一个简单的以原点为中心的2D正方形。每当我把数组的值设置为大于或等于1时，形状就会占满整个屏幕，感觉就像我只在看坐标轴的一个小部分。我试着参考NeHe的教程，改成pyopengl的版本，但我找不到我哪里出错了。

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

def display():
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)

    glBegin(GL_QUADS)
    glVertex3f(2,-2,0)
    glVertex3f(2,2,0)
    glVertex3f(-2,2,0)
    glVertex3f(-2,-2,0)
    glEnd()

    glutSwapBuffers()

if __name__ == '__main__':
    glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE | GLUT_DEPTH)
    glutInitWindowSize(640,480)
    glutCreateWindow("Hello World :'D")

    glutDisplayFunc(display)
    glutIdleFunc(display)
    glutMainLoop()

Answer 1

你需要设置投影矩阵和视口。Python让我们可以用一点函数式编程的方法来更合理地完成这件事：

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

def display(w, h):
    aspect = float(w)/float(h)
    glViewport(0, 0, w, h)
    glMatrixMode(GL_PROJECTION)
    glLoadIdentity()
    glOrtho(-aspect * 5, aspect * 5, -5, 5, -1, 1)

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity()

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)

    glBegin(GL_QUADS)
    glVertex3f(2,-2,0)
    glVertex3f(2,2,0)
    glVertex3f(-2,2,0)
    glVertex3f(-2,-2,0)
    glEnd()

    glutSwapBuffers()

def reshape(w, h):
    glutDisplayFunc(lambda: display(w, h))
    glutPostRedisplay();

if __name__ == '__main__':
    glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE | GLUT_DEPTH)
    glutInitWindowSize(640,480)
    glutCreateWindow("Hello World :'D")

    glutReshapeFunc(reshape)
    glutIdleFunc(glutPostRedisplay)
    glutMainLoop()

Answer 2

试着设置一个非默认的投影矩阵：

def display():
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)

    glMatrixMode(GL_PROJECTION)
    glLoadIdentity()
    glOrtho( 0, 640, 0, 480, -10, 10)
    glMatrixMode(GL_MODELVIEW)
    glLoadIdentity()

    ...