http://support.supermap.com.cn:8090/webgl/examples/editor.html#Particle%20System_fountain
喷泉这个例子中
viewer.scene.preUpdate.addEventListener(function (scene, time) {
particleSystem.modelMatrix = computeModelMatrix(entity, time);
// Account for any changes to the emitter model matrix.
particleSystem.emitterModelMatrix = computeEmitterModelMatrix();
});
viewer.scene.preUpdate在我这里是undefined 找不到 这个是什么意思 需要哪些js？
