Cheung, who has been working closely with director Chan Ping-chiu and 12 other actors for more than three months, thinks a lot of the time spent rehearsing is an 'extravagance', but says he enjoys the process and finds it almost a spiritual experience.

In the meantime, Cheung has been busy on other projects: promoting two commercial comedy films, House of Mahjong and It's a Wonderful Life, in which he plays supporting roles, and shooting another movie.

'Creativity requires room,' Cheung declared. 'Inspiration comes only when you are settled. Working on this play has given me time to observe things and meditate.'

Although most people know him as an actor and a stand-up comedian, Cheung is also respected within the entertainment industry as a playwright. He has received two awards for scriptwriting from the Hong Kong Federation of Drama Societies and two from the former Council for the Performing Arts, now the Hong Kong Arts Development Council.

'Drama and comedy are a part of me,' Cheung said. 'I like to communicate happiness through my acting. Acting is in the moment and it is improvisatory. But I also have a need to write scripts. This plays an important role in my character building. I take time to write my scripts, so my experiences and thoughts can settle. Writing scripts is a beautiful experience.'

Tian Gong Kai Wu, Xu Xu Ru Zhen is a complex work with two parallel plots. One traces the adventures of Xu Xu, a fictitious adolescent girl who appears in the opening sentence of the original book, and the other is based on letters written by the author to Xu Xu describing his family history and explaining why he felt compelled to create her in the first place.

'When the director Chan Ping-chiu showed me the book and said he wanted to adapt it as a play, my immediate response was to say impossible,' Cheung said. 'The story is too literary, too complicated. But it turns out that Chan and Dung Kai-cheung have done a very clever adaptation.'

The stage version keeps Xu Xu's story simple while dwelling at length on the family history aspect. Cheung plays the role of the writer. In the course of the play, everyday household objects like typewriters, washing machines and refrigerators appear, mutate and disappear.

Cheung sees Tian Gong Kai Wu, Xu Xu Ru Zhen as an expression of a writer's desire to recreate his past.

'Memories don't have to match reality exactly,' he said. 'It is how you feel now about your memories that matters. We all have different feelings for the same person or incident or thing at different times. There's no right or wrong in that.'

Cheung said that Dung was a more sentimental writer than he was. He said that if he were to write a similar book, based on memories and family history, he would take a different approach.

'I would not put as much personal feeling into my work as Dung does. I am not that introspective. When I write a script, I try to have a clear message.

'Frankly, I don't really see how my life can be meaningful to others. I write about serious subjects using dramatic and comedic modes of expression.'

Having said that, Cheung admitted to once being as sentimental as Dung, and that had helped him to empathise with the writer and his book. He, too, used to create imaginary people like Dung's Xu Xu.

'All writers like to communicate with their inner selves. I used to create another me and talk to him when I needed someone to share things with, because no one understands me better than myself.'

Cheung said Xu Xu was a complex character who served as the writer Dung's lover, mirror and confidante. He said it had been a challenge to convey the nuances of the writer's relationship with a multifaceted imaginary character.

The actor said he especially enjoyed the scenes involving a television and a typewriter, because television had been an obvious and a subtle influence on his generation while the typewriter was a tool for creative expression and resonated with Cheung's own writing experience.

Tian Gong Kai Wu: A Practical Guide to Imaginary Inventions will be staged at 7.45pm, March 5-7 and March 9-11, at the Drama Theatre of the Hong Kong Academy for Performing Arts.