openGL正交矩阵转屏幕矩阵

void display(){glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);glClearColor(1.0, 0, 0, 0);//指定视口glViewport(0, 0, 400, 400);//指定投影矩阵glMatrixMode(GL_PROJECTION);//指定以下的操作针对投影矩阵，不能少否则显示不出glLoadIdentity();//设置矩阵大小，从而将opengl的矩阵坐标转化成了屏幕坐标glOrtho(0, 400, 400, 0, -100, 100);glBegin(GL_LINES);glVertex3f(100, 300, 0);glVertex3f(0, 0, 0);glEnd();glFlush();}int main(int argc, char **argv){glutInit(&argc, argv);glutInitDisplayMode(GLUT_RGB | GLUT_SINGLE);glutInitWindowPosition(100, 100);glutInitWindowSize(400, 400);glutCreateWindow("opengl 3d view");//init();glutDisplayFunc(display);glutMainLoop();return 0;}