Question

opengl画立方体无法显示，怎么回事啊，就显示一个黑框，没有我要现实的立方体，谢谢各位解答啊，我是菜鸟

#include<GL/glut.h>

void init(void){
glutInitWindowSize(200, 150);
glClearColor(0.0,0.0,0.0,0.0);
glViewport(0,0,200,150);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(90.0f,(GLfloat)200/(GLfloat)150,1.0f,1000.0f);
}

void rect(void){
glEnable(GL_DEPTH_TEST);
glClear(GL_COLOR_BUFFER_BIT);

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glShadeModel(GL_SMOOTH );
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glColor3f(1.0,0.0,0.0);
glBegin(GL_POLYGON);
glVertex3f(0.0f, 0.0f, 0.0f); // top face
glVertex3f(0.0f, 0.0f, -1.0f);
glVertex3f(-1.0f, 0.0f, -1.0f);
glVertex3f(-1.0f, 0.0f, 0.0f);
glVertex3f(0.0f, 0.0f, 0.0f); // front face
glVertex3f(-1.0f, 0.0f, 0.0f);
glVertex3f(-1.0f, -1.0f, 0.0f);
glVertex3f(0.0f, -1.0f, 0.0f);
glVertex3f(0.0f, 0.0f, 0.0f); // right face
glVertex3f(0.0f, -1.0f, 0.0f);
glVertex3f(0.0f, -1.0f, -1.0f);
glVertex3f(0.0f, 0.0f, -1.0f);
glVertex3f(-1.0f, 0.0f, 0.0f); // left face
glVertex3f(-1.0f, 0.0f, -1.0f);
glVertex3f(-1.0f, -1.0f, -1.0f);
glVertex3f(-1.0f, -1.0f, 0.0f);
glVertex3f(0.0f, 0.0f, 0.0f); // bottom face
glVertex3f(0.0f, -1.0f, -1.0f);
glVertex3f(-1.0f, -1.0f, -1.0f);
glVertex3f(-1.0f, -1.0f, 0.0f);
glVertex3f(0.0f, 0.0f, 0.0f); // back face
glVertex3f(-1.0f, 0.0f, -1.0f);
glVertex3f(-1.0f, -1.0f, -1.0f);
glVertex3f(0.0f, -1.0f, -1.0f);
glEnd();
glFlush();
}
void main(int argc,char** argv){
glutInit(&argc,argv);
//glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
glutInitWindowPosition(100,200);
glutCreateWindow("Draw Rect");
init();
glutDisplayFunc(rect);
glutMainLoop();
}

Answer 1

gluPerspective(90.0f,(GLfloat)200/(GLfloat)150,1.0f,1000.0f);
定义的可视范围是-1.0~-1000.0，
glBegin(GL_POLYGON);
这个是画一个多边形，就是说下边全部点都将成为多边形的一个点。
glVertex3f(0.0f, 0.0f, 0.0f);
glVertex3f(0.0f, 0.0f, -1.0f);
定义的正方形的深度在0.0~-1.0，不在可视范围内。

另外正方形的顶点有错误。

追问

gluPerspective(90.0f,(GLfloat)200/(GLfloat)150,1.0f,1000.0f);
后两个参数一定要是整数才行啊，我的立方体没有问题的哈

追答

gluPerspective(90.0f,(GLfloat)200/(GLfloat)150,1.0f,1000.0f);
的最后两个参数表示Z方向上的可视范围，是浮点数，必须为正数且>0（0会出错误）。你所设定的是1.0跟1000，表示只有Z坐标在（-1.0 到 -1000）的点才能被绘制。而你下边绘制的点Z坐标都在（0 到 -1.0）所以全部看不到。另外glVertex3f(0.0f, 0.0f, 0.0f); // back face 这个真的是画错了。