胸有成竹英语是:Having a ready-formed plan

there was once an artist whose name was Wen Tong. He was famous for his bamboo drawings. A lot of people asked him for one of his bamboo drawings.

    People wondered why Wen Tong could draw so well. Actually, Wen Tong loved bamboo so much he had grown various bamboo around his house. No matter what season it was and no matter whether it was sunny or rainy, he used to go to the bamboo forest to observe how they were growing.

He carefully observed the length and breadth of the bamboo poles as well as the shapes and colors of the leaves. Whenever he found something new, he went back to his study and drew what was in his mind on paper. After a long time, the images of the bamboo in different seasons, under different weather conditions and at different moments were deeply imprinted in his mind. Whenever he stood before the paper and picked up a painting brush, various forms of bamboo came into his mind at once. So, every time he was drawing bamboo he appeared confident and at ease. All the bamboo he drew looked like real.

    When people spoke highly of his paintings, he always said modestly that he had just put the images of the bamboo imprinted in his mind in the paper.

    the phrase "having the images of bamboo ready in one's bosom" means having plans or designs ready in one's mind before doing a certain job so that its success is guaranteed. It also means being calm and sober-minded in dealing with things.