知道了为什么osg::impostor可以这样设置geometry的QUADS了

之前一直不理解为什么osg::impostor里面的impostorSprite可以直接设置impostorSprite->getCoords()来设置geometry的四个边角，其实是因为这个函数

void ImpostorSprite::drawImplementation(osg::RenderInfo& renderInfo) const，它重写了geometry的这个函数，里面直接设置了

void ImpostorSprite::drawImplementation(osg::RenderInfo& renderInfo) const
{
	osg::GLBeginEndAdapter& gl = (renderInfo.getState()->getGLBeginEndAdapter());

	// when the tex env is set to REPLACE, and the
	// texture is set up correctly the color has no effect.
	gl.Color4fv(_color.ptr());

	gl.Begin(GL_QUADS);

	gl.TexCoord2fv((GLfloat *)&_texcoords[0]);
	gl.Vertex3fv((GLfloat *)&_coords[0]);

	gl.TexCoord2fv((GLfloat *)&_texcoords[1]);
	gl.Vertex3fv((GLfloat *)&_coords[1]);

	gl.TexCoord2fv((GLfloat *)&_texcoords[2]);
	gl.Vertex3fv((GLfloat *)&_coords[2]);

	gl.TexCoord2fv((GLfloat *)&_texcoords[3]);
	gl.Vertex3fv((GLfloat *)&_coords[3]);

	gl.End();
}

　　所以可以impostorSprite->getCoords()直接设置，作用到了其成员变量，而不是通过addDrawArrays(new .....)这样来设置geometry的四个边角