OpenGL基础（四）：四边形

 OPengl中四边形的绘制类型有：GL_QUADS，GL_QUAD_STRIP和GL_POLYGON。

GL_QUADS

    依次定义四边形的各个顶点。

glPolygonMode(GL_FRONT, GL_LINE);
glBegin(GL_QUADS);
	glVertex3f(10.0f, 100.0f, 0.0f);
	glVertex3f(50.0f, 50.0f, 0.0f);
	glVertex3f(60.0f, 100.0f, 0.0f);
	glVertex3f(30.0f, 120.0f, 0.0f);

	glVertex3f(60.0f, 50.0f, 0.0f);
	glVertex3f(70.0f, 100.0f, 0.0f);
	glVertex3f(100.0f, 50.0f, 0.0f);
	glVertex3f(80.0f, 30.0f, 0.0f);
glEnd();

GL_QUAD_STRIP

    四边形带，通过共用四边形的边，减少点的个数

glPolygonMode(GL_FRONT, GL_LINE);
glBegin(GL_QUAD_STRIP);
	glVertex3f(10.0f, 100.0f, 0.0f);
	glVertex3f(50.0f, 50.0f, 0.0f);
	glVertex3f(60.0f, 100.0f, 0.0f);
	glVertex3f(60.0f, 80.0f, 0.0f);
		
	glVertex3f(80.0f, 90.0f, 0.0f);
	glVertex3f(80.0f, 70.0f, 0.0f);
glEnd();

GL_POLYGON

    多边形，通过逆时针定义多边形的点。

glPolygonMode(GL_FRONT, GL_LINE);
glBegin(GL_POLYGON);
	glVertex3f(10.0f, 100.0f, 0.0f);
	glVertex3f(50.0f, 50.0f, 0.0f);
	glVertex3f(60.0f, 80.0f, 0.0f);
	glVertex3f(60.0f, 100.0f, 0.0f);
	glVertex3f(30.0f, 120.0f, 0.0f);
glEnd();

     绘制四边形默认为填充GL_FILL，为了方便比较，启用线框模式绘制。

glPolygonMode(GL_FRONT, GL_LINE);