0180

0180=1,set_on_mission_flag_to %1d%
Description: Links a global variable to the onmission flag
Parameter 1: A global variable
Supports: GTA3, Vice City, San Andreas

This opcode links a global variable to a specific hardcoded flag that defines is there an active mission or not. Common name for that variable is $ONMISSION and it isn't recommended to change this name to prevent incompatibilies with already released scripts using $ONMISSION variable. A scripter can use the ONMISSION variable in two cases:

• Check if there's an active mission and do or not to do some actions. Commonly this check is placed at the beginning of a thread.

 0038:   $ONMISSION == 0

The original main.scm by Rockstar Games contains these checks as well.

• Notify the game that there's a running mission. When you starts a mission, you have to set the ONMISSION variable to 1. If you don't do this, your mission will work incorrectly. At the end of the mission you have to set the ONMISSION variable to 0.

The reason of setting the ONMISSION variable to 1 is that, the game, when it set to 1, constantly checks the player's state and if he's dead or busted, it automatically cancels the active mission (you fails the mission in that case). To cancel the mission correctly, Rockstar Games uses a specific mission structure as covered there. Note that mission body is placed in the gosub subroutine. If the player is dead or busted, the game automatically makes returning for all gosubs in the mission, so the execution point returns to the next opcode after gosub @MissionBegin, which is the check wasted_or_busted. This condition is true, so the script execution proceeds to the MissionFailed block.

In short, if the ONMISSION variable isn't set to 1 at the beginning of the mission, the mission couldn't be cancelled in case of player being dead or busted. Note that this only works for missions, so you can't cancel the threads in that way.

Keywords

mission, flag