Who can tell me the main idea of this poem "Traveling in a Picture World"? Every sentence should be translated. )

"It is said that after Qianlong Jiangnan returned to Beijing, he wanted to imitate the scenery of Jiangnan. Looking for a craftsman to make a model, I feel dissatisfied. Later, I saw an old man with a white beard and two maids in my dream, each with a painting axis. After opening it, the old man invited Gan Long to visit the painting. After waking up, Qianlong painted what he saw in his dream. This is traveling in a picture world. " The swaying bamboo shadows in the mountains have gone through several generations of spring and autumn. Clouds are high and light, and rivers flow by themselves. Wan Li on the Yangtze River is like a jade belt. The bright moon is like a rolling golden ball. The mountains and rivers in the painting, from three thousand miles in Hubei to sixteen states in the south of the Yangtze River. I can't see this beautiful scenery for a while, but I hope I can have a chance to see the paintings again.