Crate bevy_system_graph
source ·Expand description
This crate provides the utilities for creating strictly ordered execution graphs of systems for the Bevy game engine.
Starting a Graph
To start building a system graph, one or more systems must be added to the graph as root nodes. Root systems have no dependencies within the graph.
let graph = SystemGraph::new();
// Create a root system for the graph.
let root_a = graph.root(sys_a);
// Graphs can have multiple root nodes.
let root_b = graph.root(sys_b);
let root_c = graph.root(sys_c);
Using SystemLabels
Systems can still use labels to establish the ordering of systems relative to other systems outside of the graph.
let graph = SystemGraph::new();
let root_a = graph.root(
sys_a
.label("Physics")
.before("Propagate Transforms")
);
Conversion into SystemSet
To ease adding all of the graph’s systems into a Schedule
, both
SystemGraph
and SystemGraphNode
implement Into<SystemSet>
.
let graph = SystemGraph::new();
let root_a = graph.root(sys_a);
// Convert into a SystemSet
let system_set: SystemSet = graph.into();
Sequential Execution
Graph nodes can be sequentially chained via SystemGraphNode::then
. This
creates a new node from a system and adds a “after” dependency on the original
system.
let graph = SystemGraph::new();
graph
.root(sys_a)
.then(sys_b)
.then(sys_c);
// Convert into a SystemSet
let system_set: SystemSet = graph.into();
Fan Out
SystemGraphNode::fork
can be used to fan out into multiple branches. All fanned out systems will not execute
until the original has finished, but do not have a mutual dependency on each other.
let graph = SystemGraph::new();
// Fork out from one original node.
// sys_b, sys_c, and sys_d will only start when sys_a finishes.
let (c, b, d) = graph.root(sys_a)
.fork((
sys_b,
sys_c,
sys_d,
));
// Alternatively, calling "then" repeatedly achieves the same thing.
let e = d.then(sys_e);
let f = d.then(sys_f);
// Convert into a SystemSet
let system_set: SystemSet = graph.into();
Fan In
A graph node can wait on multiple systems before running via SystemJoin::join
.
The system will not run until all prior systems are finished.
let graph = SystemGraph::new();
let start_a = graph.root(sys_a);
let start_b = graph.root(sys_b);
let start_c = graph.root(sys_c);
(start_a, start_b, start_c)
.join(sys_d)
.then(sys_e);
// Convert into a SystemSet
let system_set: SystemSet = graph.into();
Fan Out into Fan In
The types used to implement fork and join are composable.
let graph = SystemGraph::new();
graph.root(sys_a)
.fork((sys_b, sys_c, sys_d))
.join(sys_e)
.then(sys_f);
// Convert into a SystemSet
let system_set: SystemSet = graph.into();
Cloning
Individual graph nodes are backed by a Rc
, so cloning it will still
point to the same logical underlying graph.
Structs
SystemStage
.SystemGraph
that represents a system.Traits
SystemGraph
s.SystemGraphNode
s that can be joined together into one or more dependent
systems.