- Hand grenades are both dynamically created during the course of a game (when the player throws them) and dynamically removed again (after they have exploded and their traces have gone). This makes them different from many other entities that are defined in map files and often exist from the beginning to the end of the map.
- Hand grenades employ more components than other entities in order to implement their functionality:
- Model (the hand grenade model as thrown through the map),
- Physics (for computing the flight path and dealing with collisions, e.g. with walls and the floor),
- Script (for controlling the details, e.g. letting the detonation timer tick and implementing the explosion effects),
- Light (for the flare when the hand grenade explodes),
- Sound (for the sound at the time of the explosion),
- ParticleSystem (for the smoke and spark particles at the explosion).
- They very well demonstrate the distinction between Server State and Client Effects.
The server state is characterized by the following properties:
- It is synchronized via the game server to all clients,
- every player (client) sees the same results and consequences,
- server state is relevant for gameplay.
As a side note, events are often a result of a change in the server state, and transferred to the clients as such.
Client effects can be triggered by some event in the server state, but besides that, they:
- run independently of each other on the clients only,
- are often used for eye-candy,
- it's ok if not everyone sees exactly the same (not relevant for gameplay).
An important insight is that we sometimes need both server state and client effects combined.
For example, consider a light source that illuminates an otherwise pitch black part of a labyrinth. Whether the light source is on or off clearly makes an important difference for players who try to navigate the labyrinth, and so the state of the light source is managed as a part of the server state.
However, there are also other kinds of light sources, e.g. those that are on, but steadily flicker or pulse. This is often a means to create a specific atmosphere to a map, but the exact amplitude of the flicker or pulse is really not something that needs synchronization over the network.
In fact, as a combination we may wish that the light source's on or off state is synchronized to everyone, and if it is on, have it have a client-side flicker effect for eye-candy.
This is exactly what we can (starting with commit d11c6a9) achieve with the light source components, and what I now employ with the hand grenades: When a hand grenade explodes, the related light source is turned on in order to mimic the bright flare of the explosion. However, the exact details of how the bright light fades, changes its color from white over yellow to red, shrinks and eventually disappears (all in about half a second), needs not be synchronized over the network.
Instead, a very simple script method is used to implement this. Here is its entire code:
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local clTime = 0.0 local Duration = 0.5 function Light:ClientEffect(t) if not self:get("On") then clTime = 0.0 return false end clTime = clTime + t if clTime >= Duration then return true, 0, 0, 0, 0 end local Amount = 1.0 - clTime/Duration return true, Amount, Amount*Amount, Amount*Amount*Amount, 400.0 end