打开GL：在简单的3D线上显示空白窗口

Question

#include <GL/freeglut.h>
#include <stdlib.h>
void vertex()
{
glLineWidth(5.0);
glBegin(GL_LINES);
{
glColor3f(1,0.5,0.0);//colour added 
glVertex3f(0.0,0.0,0.0);
glVertex3f(0.0,5.0,9.0);
}
glEnd();
glutPostRedisplay();
}
void myDisplay(void)
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glLoadIdentity();//load the identity matrix
vertex(); 
glutSwapBuffers();
}
void initializeGL(void)
{
glFlush();//initialize the screen before adding any elements
glEnable(GL_DEPTH_TEST);
glEnable (GL_BLEND);
glBlendFunc (GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
glClearColor(0,0,0,1.0);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(-70.0,70.0,-70.0,70.0,0.01,80.0);//set the max mins for x,y and z
glMatrixMode(GL_MODELVIEW);
}
int main(int argc, char** argv)
 {
glutInit(&argc,argv);
glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH); 
glutInitWindowSize(500,500);
glutInitWindowPosition(100,150);
glutCreateWindow("3D line"); 
glutDisplayFunc(myDisplay);
glEnable(GL_DEPTH_TEST);
initializeGL();
glutMainLoop();}

这个程序应该只在3D中创建一条橙色线，但似乎每次都会给我一个黑屏。我确保交换缓冲区，因为我使用的是双缓冲区，每次它通过顶点时我都会重新显示。不确定是什么问题

Answer 1

您正在视图截头体外部进行绘制glOrtho定义了一个截头体，该截头体在z维度上限制为[-near，-far]（注意负号）。