NEW YORK (NYTIMES) - The online game unfolds from the point of view of an attacker, aiming a weapon down a school corridor or throwing a grenade into an auditorium.
The character creeps around corners and up staircases. Bullets spray, blood spatters. SWAT team members are shot dead. Civilians are splayed out on the floor.
The game is "Active Shooter", and it is not scheduled to be released until June 6.
But it has already run into controversy after several recent school shootings, including massacres at high schools in Santa Fe, Texas, and Parkland, Florida.
Parents of victims of the Parkland shooting have amplified the opposition to the game, calling for boycotts and seeking to block its release.
"Nothing will bring my daughter back, but there is a role for adults to have in terms of being responsible, and this is not responsible," said Mr Fred Guttenberg, whose daughter, Jaime, was one of the 17 victims of the Feb 14 shooting in Parkland.
"This is gross, this is profiteering, this is unacceptable."
"Active Shooter" was developed by Acid Publishing Group, which has an online page in English and Russian.
The developer is planning to sell the game for US$5 to US$10 (S$6.73-S$13.46) on Steam, a publishing marketplace run by Valve Corp of Bellevue, Washington.
Discussion about violent video games and their impact on young people's behaviour was renewed after the Parkland shooting, which the police said was carried out by a former student, Nikolas Cruz.
A neighbour said Cruz spent long hours playing video games. President Donald Trump said after the shooting that he was "hearing more and more people say the level of violence on video games is really shaping young people's thoughts".
Researchers have rejected such claims many times as the number of mass shootings has increased over the past two decades.
An online petition to stop the release of the game had gathered more than 100,000 signatures as of Tuesday (May 29) afternoon.
Valve and Acid's developer, Revived Games, did not reply to requests for comment on Tuesday.
Acid said in a blog post last week that the game "does not promote any sort of violence, especially any (sort) of a mass shooting".