An image from the video game That Dragon, Cancer, as seen in Thank You for Playing (Tribeca Film Festival)

Joel Green is diagnosed with terminal brain cancer at the age of 12 months and given just three months to live, but at three years old, he’s still alive, and the cancer, while still present, has stabilized. His father, Ryan, a professional programmer drawn to video game design, is already well into the creation of a project that serves as a coping mechanism for himself and a memorial to Joel’s life and battle with cancer.

The documentary follows Ryan’s development of the game, That Dragon, Cancer, from the time Joel is three until his death at five. While the game is an integral part of the film, the primary focus is on how the Green family, and Ryan in particular, deals with the devastating reality of having a child with a terminal illness. Ryan’s internal struggle with hope versus the inevitability of Joel’s diagnosis drives the creative decisions that ultimately result in the groundbreaking game’s design.

Despite stating that his purpose for making the game is “to create a space to talk about my son,” Ryan decides that the child in the game should have no distinguishing features. Ostensibly, this serves to allow players to become more personally involved by mentally projecting an image from their own lives onto the face of the child, but it also allows Ryan to maintain a somewhat objective distance so that the game doesn’t become as overwhelming as his real life. He also chooses not to include the recorded sound of Joel’s crying even though he has recorded Joel’s laughter for the game. Instead, he dubs in another child’s cry for the soundtrack.

One of the strengths of the film is that it does not dwell on Joel’s deterioration. Instead, there are intermittent but numerous clips of happy times shared with the family. The film dwells instead on the complex emotions and unanswerable questions that assail Ryan and his wife, Amy, on a daily basis. Ryan declares that, “I want to bring players face-to-face with that shadow of death and ask them what they really believe,” because it is clear that he is no longer sure himself.

Perhaps the most emotionally wrenching part of the film is when Ryan previews the unfinished product at a gaming convention. Players proceed through the game in stunned silence or with tears streaming down their faces, exiting the booth with few words and with brief physical gestures of solace for Ryan.

All the prayers in the world cannot change the outcome, so in the game there are neither points to be won nor an end goal to achieve. The ending is a foregone conclusion. There is a story component, and powerful surrealistic visuals, but the documentary is sparing in what it reveals about the game since it was still a work in progress during the filming.

Was this heart-wrenching movie created to provide context for and pique interest in Ryan’s unusual game or to permanently capture Joel’s brief place within the Green family? Probably both. Dedicated gamers and game designers will certainly want to explore Thank You for Playing. People facing a similar loss may find the game therapeutic, and others may see it as a way to explore their feelings about death. For the Greens, the film will always stand as a testament to their love for Joel, and to their ability to stand together.