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@@ -85,9 +85,9 @@ Group
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Mask
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: The other _groups_ this object should collide with. You can name one group or specify multiple groups in a comma separated list. If you leave the Mask field empty, the object will not collide with anything.
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-### Units used
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+### Units used by the physics engine simulation
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-The physics engine simulates Newtonian physics and it is designed to work well with meters, kilograms and seconds (MKS) units. Furthermore, the physics engine is tuned to work well with moving objects of a size in the 0.1 to 10 meters range (static objects can be larger) and by default the engine treats 1 unit (pixel) as 1 meter. This conversion between pixels and meters is convenient on a simulation level, but from a game creation perspective it isn't very useful. With default settings a collision shape with a size of 200 pixels would be treated as having a size of 200 meters which is well outside of the recommended range, at least for a moving object. In general it is required that the physics simulation is scaled for it to work well with the typical size of objects in a game. The scale of the physics simulation can be changed in `game.project` via the [physics scale setting](/manuals/project-settings/#_physics). Setting this value to for instance 0.02 would mean that a 200 pixels would be treated as a 4 meters. Do note that the gravity (also changed in `game.project`) has to be increased to accommodate for the change in scale.
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+The physics engine simulates Newtonian physics and it is designed to work well with meters, kilograms and seconds (MKS) units. Furthermore, the physics engine is tuned to work well with moving objects of a size in the 0.1 to 10 meters range (static objects can be larger) and by default the engine treats 1 unit (pixel) as 1 meter. This conversion between pixels and meters is convenient on a simulation level, but from a game creation perspective it isn't very useful. With default settings a collision shape with a size of 200 pixels would be treated as having a size of 200 meters which is well outside of the recommended range, at least for a moving object. In general it is required that the physics simulation is scaled for it to work well with the typical size of objects in a game. The scale of the physics simulation can be changed in `game.project` via the [physics scale setting](/manuals/project-settings/#_physics). Setting this value to for instance 0.02 would mean that 200 pixels would be treated as a 4 meters. Do note that the gravity (also changed in `game.project`) has to be increased to accommodate for the change in scale.
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## Group and mask
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@@ -294,3 +294,8 @@ function on_message(self, message_id, message, sender)
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end
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end
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```
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+
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+## Caveats and common issues
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+
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+Collection proxies
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+: Through collection proxies it is possible to load more than one top level collection, or *game world* into the engine. When doing so it is important to know that each top level collection is a separate physical world. Physics interactions (collisions, triggers, ray-casts) only happen between objects belonging to the same world. So even if the collision objects from two worlds visually sits right on top of each other, there cannot be any physics interaction between them.
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Björn Ritzl