问一个opengl视点的问题

[Areslp]

我采用正交投影，但是发现当一个平面转到与视景体的上、下面平行的时候，应该有一根线，但是现在显示不出来，也没有发现是哪里错了，请大家指教。、

设置视点代码：width和height是窗口的宽，高
glViewport(0,0,width,height);
aspect = (GLdouble)width/(GLdouble)height;
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
gluLookAt(0.0,0.0,20.0,0.0,0.0,0.0,0.0,1.0,0.0);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
float h=20.0f;
glOrtho(-h*aspect,h*aspect,-h,h,0.0,40.0);

画三角形：
boost::shared_ptr<Triangle> triangle_ptr(new Triangle(Point(-10.0f,0.0f,10.0f),Point(10.0f,0.0f,0.0f),Point(-10.0f,0.0f,0.0f)));-->平行于xoz面的三角形
m_scene->add_child(triangle_ptr);

请问问题出在哪里？

[dukelee]

我写了个测试程序：

#include <GL/glut.h>
#include <stdlib.h>
#include <windows.h>
#include "math.h"
//using namespace std;
#define PI 3.1415926


void myinit()
{
	glClearColor(1.0, 1.0, 1.0, 0.0);
	glShadeModel(GL_FLAT);
	glEnable(GL_LINE_SMOOTH);
	glHint(GL_LINE_SMOOTH_HINT, GL_DONT_CARE);
	
	glEnable(GL_BLEND); 
	glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
	glEnable(GL_LINE_SMOOTH);

}

void resize(int w, int h)
{
	glViewport(0,0,w,h);
	GLfloat aspect = (GLfloat)w/(GLfloat)h;
	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();
	gluLookAt(0.0,0.0,20.0,0.0,0.0,0.0,0.0,1.0,0.0);
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	float hh=20.0f;
	glOrtho(-hh*aspect,hh*aspect,-hh,hh,0.0,40.0);
	glMatrixMode(GL_MODELVIEW); //这句加一下
}

void mydraw()
{
	float a[]={-10.0,0.0,10.0};
	float b[]={10.0,0.0,0.0};
	float c[]={-10.0,0.0,0.0};

	glClear(GL_COLOR_BUFFER_BIT);
	glLoadIdentity();
	glColor3f(1.0, 0.0, 1.0);
	glEnable(GL_POINT_SMOOTH);
	glPointSize(1.0);
	glBegin(GL_LINE_LOOP);
	glVertex2fv(a);
	glVertex2fv(b);
	glVertex2fv(c);
	glEnd();
	glFlush();
}

int main(int argc, char** argv)
{
	glutInit(&argc, argv);
	glutInitDisplayMode (GLUT_SINGLE| GLUT_RGB);
	glutInitWindowSize(600,600);
	glutCreateWindow("PttoCircle");
	myinit();
	
	glutReshapeFunc(resize);
	glutDisplayFunc(mydraw);
	//glutKeyboardFunc(keyboard);
	//glutMouseFunc(mouse);
	//glutMotionFunc(mousemove);
	//glutIdleFunc(Idlefn);
	glutMainLoop();
	return 0;
}

[Areslp]

谢了，好像确实这个glBegin(GL_LINE_LOOP);模式没选对的问题，我是这样画的

glBegin(GL_POLYGON);
		glVertex3f(m_p0.m_x,m_p0.m_y,m_p0.m_z);
		glVertex3f(m_p1.m_x,m_p1.m_y,m_p1.m_z);
		glVertex3f(m_p2.m_x,m_p2.m_y,m_p2.m_z);
	glEnd();

用GL_LINE_LOOP就能看到