RTT相机

osg::Camera* createHUDCamera(double left, double right, double bottom, double top)
{
	osg::ref_ptr<osg::Camera> camera = new osg::Camera();

	camera->setProjectionMatrix(osg::Matrix::ortho2D(left, right, bottom, top));

	camera->setReferenceFrame(osg::Transform::ABSOLUTE_RF);
	camera->setViewMatrix(osg::Matrix::identity());

	camera->setClearMask(GL_DEPTH_BUFFER_BIT);
	camera->setRenderOrder(osg::Camera::POST_RENDER);

	camera->setAllowEventFocus(false);

	camera->getOrCreateStateSet()->setMode(GL_LIGHTING, osg::StateAttribute::OFF);

	return camera.release();
}

osg::Camera* createHUDNode(osg::Texture2D* texture)
{
	osg::ref_ptr<osg::Camera> hud_camera = createHUDCamera(0, 500, 0, 400);

	osg::ref_ptr<osg::Geode> geode = new osg::Geode();
	geode->getOrCreateStateSet()->setMode(GL_LIGHTING, osg::StateAttribute::OFF);
	geode->getOrCreateStateSet()->setTextureAttributeAndModes(0, texture);
	osg::ref_ptr<osg::Geometry> geometry = osg::createTexturedQuadGeometry(osg::Vec3(), osg::Vec3(100.0f, 0.0f, 0.0f), osg::Vec3(0.0f, 100.0f, 0.0f));
	geode->addDrawable(geometry);
	hud_camera->addChild(geode);

	return hud_camera.release();
}

void createSlaveCamera(osgViewer::Viewer* viewer, osg::Texture2D* texture)
{
	osg::ref_ptr<osg::GraphicsContext> gc = viewer->getCamera()->getGraphicsContext();
	int width = gc->getTraits()->width;
	int height = gc->getTraits()->height;

	osg::ref_ptr<osg::Camera> camera = new osg::Camera();
	camera->setRenderOrder(osg::Camera::PRE_RENDER);
	camera->setGraphicsContext(gc);
	camera->setViewport(0, 0, width, height);
	camera->attach(osg::Camera::COLOR_BUFFER, texture);
	viewer->addSlave(camera, osg::Matrixd::scale(5, 5, 5), osg::Matrixd::identity());
}

int main()
{
	osgViewer::Viewer viewer;
	viewer.setUpViewInWindow(0, 0, 500, 400);
	viewer.realize();

	osg::ref_ptr<osg::Group> group = new osg::Group();

	osg::ref_ptr<osg::Node> cow = osgDB::readNodeFile("cow.osg");
	group->addChild(cow);

	osg::ref_ptr<osg::Texture2D> texture = new osg::Texture2D();
	texture->setInternalFormat(GL_RGBA);
	group->addChild(createHUDNode(texture));

	createSlaveCamera(&viewer, texture);

	viewer.setSceneData(group);
	return viewer.run();
}