In the fiftieth chapter of A Dream of Red Mansions, there is a description of rhyming writing:
Baochai had to agree and added, "Let's use the word Hongmei as the rhyme, each with seven tones. Sister Xing is a scarlet letter, sister Li is a plum character, and the harp is a flower character. "
So the poems written by three people are: "Red" means Hongmei (Xing Xiuyan), "Mei" means Hongmei (Wenli) and "Flower" means Hongmei (Xue Baoqin).
Du Fu's poem should be a banquet ordered by Baishui County. Most of them found a poem or something on the spot, and everyone took turns to take a word from it as rhyme. Du Fu was given the word "Guo", so this poem he wrote used the rhyme of five songs where the word "Guo" was located.