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[wpilib] Add EventLoop (#4104)
This is a generic expansion of the command-based Trigger framework.
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// Copyright (c) FIRST and other WPILib contributors.
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// Open Source Software; you can modify and/or share it under the terms of
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// the WPILib BSD license file in the root directory of this project.
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package edu.wpi.first.wpilibj.event;
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import static edu.wpi.first.util.ErrorMessages.requireNonNullParam;
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import edu.wpi.first.math.filter.Debouncer;
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import java.util.function.BiFunction;
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import java.util.function.BooleanSupplier;
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/**
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* This class provides an easy way to link actions to high-active logic signals. Each object
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* represents a digital signal to which callback actions can be bound using {@link
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* #ifHigh(Runnable)}.
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*
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* <p>These signals can easily be composed for advanced functionality using {@link
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* #and(BooleanSupplier)}, {@link #or(BooleanSupplier)}, {@link #negate()} etc.
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*
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* <p>To get an event that activates only when this one changes, see {@link #falling()} and {@link
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* #rising()}.
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*/
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public class BooleanEvent implements BooleanSupplier {
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/** Poller loop. */
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protected final EventLoop m_loop;
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/** Condition. */
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private final BooleanSupplier m_signal;
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/**
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* Creates a new event with the given signal determining whether it is active.
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*
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* @param loop the loop that polls this event
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* @param signal the digital signal represented by this object.
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*/
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public BooleanEvent(EventLoop loop, BooleanSupplier signal) {
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m_loop = requireNonNullParam(loop, "loop", "BooleanEvent");
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m_signal = requireNonNullParam(signal, "signal", "BooleanEvent");
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}
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/**
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* Check the state of this signal (high or low).
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*
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* @return true for the high state, false for the low state.
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*/
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@Override
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public final boolean getAsBoolean() {
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return m_signal.getAsBoolean();
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}
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/**
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* Bind an action to this event.
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*
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* @param action the action to run if this event is active.
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*/
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public final void ifHigh(Runnable action) {
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m_loop.bind(m_signal, action);
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}
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/**
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* Get a new event that events only when this one newly changes to true.
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*
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* @return a new event representing when this one newly changes to true.
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*/
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public BooleanEvent rising() {
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return new BooleanEvent(
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m_loop,
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new BooleanSupplier() {
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private boolean m_previous = m_signal.getAsBoolean();
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@Override
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public boolean getAsBoolean() {
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boolean present = m_signal.getAsBoolean();
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boolean ret = !m_previous && present;
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m_previous = present;
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return ret;
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}
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});
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}
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/**
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* Get a new event that triggers only when this one newly changes to false.
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*
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* @return a new event representing when this one newly changes to false.
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*/
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public BooleanEvent falling() {
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return new BooleanEvent(
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m_loop,
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new BooleanSupplier() {
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private boolean m_previous = m_signal.getAsBoolean();
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@Override
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public boolean getAsBoolean() {
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boolean present = m_signal.getAsBoolean();
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boolean ret = m_previous && !present;
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m_previous = present;
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return ret;
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}
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});
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}
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/**
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* Creates a new debounced event from this event - it will become active when this event has been
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* active for longer than the specified period.
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*
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* @param seconds The debounce period.
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* @return The debounced event (rising edges debounced only)
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*/
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public BooleanEvent debounce(double seconds) {
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return debounce(seconds, Debouncer.DebounceType.kRising);
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}
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/**
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* Creates a new debounced event from this event - it will become active when this event has been
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* active for longer than the specified period.
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*
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* @param seconds The debounce period.
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* @param type The debounce type.
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* @return The debounced event.
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*/
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public BooleanEvent debounce(double seconds, Debouncer.DebounceType type) {
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return new BooleanEvent(
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m_loop,
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new BooleanSupplier() {
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private final Debouncer m_debouncer = new Debouncer(seconds, type);
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@Override
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public boolean getAsBoolean() {
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return m_debouncer.calculate(m_signal.getAsBoolean());
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}
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});
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}
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/**
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* Creates a new event that is active when this event is inactive, i.e. that acts as the negation
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* of this event.
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*
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* @return the negated event
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*/
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public BooleanEvent negate() {
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return new BooleanEvent(m_loop, () -> !m_signal.getAsBoolean());
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}
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/**
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* Composes this event with another event, returning a new signal that is in the high state when
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* both signals are in the high state.
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*
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* <p>The new event will use this event's polling loop.
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*
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* @param other the event to compose with
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* @return the event that is active when both events are active
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*/
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public BooleanEvent and(BooleanSupplier other) {
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requireNonNullParam(other, "other", "and");
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return new BooleanEvent(m_loop, () -> m_signal.getAsBoolean() && other.getAsBoolean());
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}
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/**
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* Composes this event with another event, returning a new signal that is high when either signal
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* is high.
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*
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* <p>The new event will use this event's polling loop.
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*
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* @param other the event to compose with
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* @return a signal that is high when either signal is high.
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*/
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public BooleanEvent or(BooleanSupplier other) {
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requireNonNullParam(other, "other", "or");
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return new BooleanEvent(m_loop, () -> m_signal.getAsBoolean() || other.getAsBoolean());
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}
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/**
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* A method to "downcast" a BooleanEvent instance to a subclass (for example, to a command-based
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* version of this class).
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*
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* @param ctor a method reference to the constructor of the subclass that accepts the loop as the
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* first parameter and the condition/signal as the second.
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* @param <T> the subclass type
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* @return an instance of the subclass.
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*/
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public <T extends BooleanEvent> T castTo(BiFunction<EventLoop, BooleanSupplier, T> ctor) {
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return ctor.apply(m_loop, m_signal);
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}
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}
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@@ -0,0 +1,50 @@
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// Copyright (c) FIRST and other WPILib contributors.
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// Open Source Software; you can modify and/or share it under the terms of
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// the WPILib BSD license file in the root directory of this project.
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package edu.wpi.first.wpilibj.event;
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import java.util.Collection;
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import java.util.LinkedHashSet;
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import java.util.function.BooleanSupplier;
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/** The loop polling {@link BooleanEvent} objects and executing the actions bound to them. */
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public final class EventLoop {
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private final Collection<Binding> m_bindings = new LinkedHashSet<>();
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/**
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* Bind a new action to run whenever the condition is true.
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*
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* @param condition the condition to listen to.
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* @param action the action to run.
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*/
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public void bind(BooleanSupplier condition, Runnable action) {
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m_bindings.add(new Binding(condition, action));
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}
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/** Poll all bindings. */
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public void poll() {
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m_bindings.forEach(Binding::poll);
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}
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/** Clear all bindings. */
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public void clear() {
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m_bindings.clear();
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}
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private static class Binding {
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private final BooleanSupplier m_condition;
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private final Runnable m_action;
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private Binding(BooleanSupplier condition, Runnable action) {
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this.m_condition = condition;
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this.m_action = action;
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}
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void poll() {
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if (m_condition.getAsBoolean()) {
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m_action.run();
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}
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}
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}
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}
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