This function will set the shape of the particle group that is being created. You must first have begun the group definition using the function physics_particle_group_begin(), and then you would use this function to set the approximate half width and half height of the group in pixels - approximate because the exact width and height will depend on the size of the base particles, as defined by the physics_particle_set_radius() function, as the physics simulation tries to "fit" as many of the particles as possible into the defined shape. Finally you need to call physics_particle_group_end() to create the group of particles in the room.
|halfWidth||The half width of the box.|
|halfHeight||The half height of the box.|
var flags = phy_particle_flag_water |
phy_particle_flag_viscous | phy_particle_flag_tensile;
var groupflags = phy_particle_group_flag_solid;
physics_particle_group_begin(flags, groupflags, mouse_x, mouse_y, 0, 0, 0, 0, c_white, 1, 1, 2);
mLastGroup = physics_particle_group_end();
The above code stores the flags for the particle type and the particle group properties in variables then uses these to create a rectangular particle group with with sides of 200px at the mouse position.