physics_mass_properties(mass, local_center_x, local_center_y, inertia)
| Argument | Description |
|---|---|
| mass | The new mass that you want the fixture to have. |
| local_center_x | The local x coordinate of the new center of mass. |
| local_center_y | The local y coordinate of the new center of mass. |
| inertia | Set the inertia for the fixture. |
Returns: N/A
This function can be used to set custom mass and inertia values
for a physics enabled instance. Normally the mass, center of mass,
and inertia for an instance is calculated using a combination the
surface area of the bound fixtures and their density. However in
very special occasions you may need to offset the center of mass or
change the inertia and that is when you would use this function.
Bear in mind that the mass is calculated in real world weight
(ie:kilograms) and you should always try and keep values realistic
for what you are modelling. So if your physics object is meant to
represent a person, their mass would be approximately 70 kilos.
The center of mass is calculated automatically for you based on the
shape of the fixture (or fixtures) you have defined. To get a
general idea of where this could be, if you have a sprite that is
the same shape as the fixtures you wish to create, then select the
"center origin" option you will see approximately where the center
of mass will be too. However, this may not be correct or you may be
looking for a specific effect from your physics object, in which
case this function can also be used to change the x and y
coordinates for the center of mass. These are local values,
so 0,0 is the point at which the fixtures are bound to the instance
(the origin of the instance). So a center of mass of -4,0 would
shift the center of mass to the left of the origin.
As for the inertia, this basically defines how resistant the
instance is to changes in its direction and velocity, so a higher
inertia makes it more resistant and a low inertia makes it less
resistant (inertia and mass cannot be negative values!).
NOTE: This function does not set mass and inertia for
individual fixtures, but rather for the whole physics enabled
instance, no matter how many fixtures are bound to it.
NOTE: This function should only be used when necessary as
the physics simulation is designed for the mass and inertia to be
optimal based on the density and size of the fixture. Changing
these values can have unforeseen effects.
physics_mass_properties(phy_mass, -10, -10, phy_inertia);
The above code will shift the center of mass of the physical body to the left.