opengl中如何使窗口大小改变时，图形的形状不发生变化？

问题的关键在于设置裁剪区域的纵横比与视口的纵横比一致。

设置视口大小：

glViewport(GLint x,GLint y,GLsizei w,GLsizei h);

(x,y)是视口距离窗口左下角的位置，(w,h)是视口的宽度和高度。

设置二维观察函数：

glOrtho2D(GLdouble left,GLdouble right,GLdouble bottom,GL double top);

锁定纵横比，注意这里为什么要加一个判断语句。比如当窗口的宽大于高时（w>h），裁剪区域只能设置将高扩大即：（-15.0/ratio,15.0/ratio），而不能设置将宽缩小（这样会使图像在w方向的部分显示不出来）

glViewport(0,0,w,h);
GLfloat ratio=(GLfloat)w/(GLfloat)h;
if(w<=h)//保持形状不变
		gluOrtho2D(-15.0,15.0,-15.0/ratio,15.0/ratio);
else
		gluOrtho2D(-15.0*ratio,15.0*ratio,-15.0,15.0);

具体代码：

#include 
#include 
GLfloat v[3][3]={{-10.0,0.0,0.0},{10.0,0.0,0.0},{0.0,10.0,0.0}};
int num=5;
void reshape(GLsizei w,GLsizei h)
{
	GLfloat ratio=(GLfloat)w/(GLfloat)h;
	glViewport(0,0,w,h);
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	if(w<=h)//保持形状不变
		gluOrtho2D(-15.0,15.0,-15.0/ratio,15.0/ratio);
	else
		gluOrtho2D(-15.0*ratio,15.0*ratio,-15.0,15.0);
	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();
}
void triangle(GLfloat* a,GLfloat* b,GLfloat* c)
{
	glVertex3fv(a);
	glVertex3fv(b);
	glVertex3fv(c);
}
void divide_triangle(GLfloat* a,GLfloat* b,GLfloat* c,int n)
{
	GLfloat ab[3],ac[3],bc[3];
	if(n>0)
	{
		for(int j=0;j<3;j++)
		{
			ab[j]=(a[j]+b[j])/2;
			ac[j]=(a[j]+c[j])/2;
			bc[j]=(b[j]+c[j])/2;
		}
		divide_triangle(a,ab,ac,n-1);
		divide_triangle(ab,b,bc,n-1);
		divide_triangle(ac,bc,c,n-1);
	}
	else triangle(a,b,c);
}
void display()
{	
	glClear(GL_COLOR_BUFFER_BIT);
	glBegin(GL_TRIANGLES);
	divide_triangle(v[0],v[1],v[2],num);
	glEnd();
	glFlush();
}
void myInit()
{
	glClearColor(1.0,1.0,1.0,1.0);
	glColor3f(0.0,1.0,0.0);
	glViewport(0,0,500,500);
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	gluOrtho2D(-15.0,15.0,-15.0,15.0);
	glMatrixMode(GL_MODELVIEW);
}
void main(int argc,char** argv)
{
	glutInit(&argc,argv);
	glutInitDisplayMode(GLUT_SINGLE|GLUT_RGB);
	glutInitWindowSize(500,500);
	glutInitWindowPosition(0,0);
	glutCreateWindow("Sierpinski");
	glutReshapeFunc(reshape);
	glutDisplayFunc(display);
	myInit();
	glutMainLoop();
}

运行结果截图：

参考文献：《交互式计算机图形学》（第五版） Edward Angel等