Question

OpenGL中的画线

有这么一段程序：
void CGfxOpenGL::Render()
{
float lineWidth = 0.5;

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // clear screen and depth buffer
glLoadIdentity();
gluLookAt(0.0, 10.0, 0.1, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);

float line;
// draw a series of lines of increasing width
for (line = 0.0; line < 7.0; line+=0.5)
{
// set the line width
glLineWidth(lineWidth);

// draw the line
glBegin(GL_LINES);
glVertex3f(-5.0, 0.0, line-3.0f);
glVertex3f(-1.0, 0.0, line-3.0f);
glEnd();

// increase the line width for the next point
lineWidth += 1.0;
}

// reset line width
lineWidth = 0.5;

// enable stippling
glEnable(GL_LINE_STIPPLE);

// 0xAAAA = 1010 1010 1010 1010
short stipplePattern = 0xAAAA;

// set the stipple pattern
glLineStipple(2, stipplePattern);

// draw a series of lines of increasing width with stippling
for (line = 0.0; line < 7.0; line+=0.5)
{
// set the line width
glLineWidth(lineWidth);

// draw the point
glBegin(GL_LINES);
glVertex3f(1.0f, 0.0f, line-3.0f);
glVertex3f(5.0f, 0.0f, line-3.0f);
glEnd();

// increase the point size for the next point
lineWidth += 1.0;
}

glDisable(GL_LINE_STIPPLE);
}

明明前面应该是画一系列的实线，为什么运行之后只过了几秒钟，它就变成跟后面一样是点划线了呢？
那应该怎么设置呢？才能让各自显示各自的图形呢？

Answer 1

开始时，默认下是采用实线模式的，所以前面开始是实线，后面你启用了点划模式，所以后面是点划线，OpenGL保留了这个状态，经过glutMainLoop后，重画，采用的点划线的方式，所以前面的直线也是点划线了