Add replacement PIDController class (#1300)

Originally, PIDController used PIDSource with its "PIDSourceType" to
determine whether a class should return position or velocity to the
controller. However, the supported languages have changed a lot over 10
years and now support lambdas. Instead of using PIDSource and PIDOutput,
users can pass in doubles to the Calculate() function synchronously.
This makes the controller much more flexible for team's needs as they no
longer have to make a separate PIDSource-inheriting class just to
provide a custom input.

The built-in feedforward was removed. Since PIDController is synchronous
now, they can add their own feedforward on top of what Calculate()
returns.

To facilitate running the controller asynchronously, there is a
PIDControllerRunner class that handles that. By separating the loop from
the control law, PIDController can now be composed with others and be
used to control a drivetrain (a multiple input, multiple output system
that requires summing the results from two controllers) much easier.
Also, motion profiling can be used to set the reference over time.

All the classes related to the old PIDController are now deprecated. The
new classes are in an experimental namespace to avoid name conflicts.

While this is a large change, I think it is a necessary one for growth.
The old PIDController design was created in a time when languages only
supported OOP, and we have more tools at our disposal now to solve
problems. This more versatile implementation can be used in more places
like as a replacement for Pathfinder's "EncoderFollower" class.

There has been hesitation to add lambda support to WPILib for a while
now out of concerns for requiring teams to learn more features of C++ or
Java. In my opinion, this change makes PIDController easier to use, not
harder. The concept of a function is a building block of OOP and should
be learned before classes. The ability to store functions as first-class
objects and invoke them just like variables is rather natural.

Note that PID constants for the new controller will be different from
the old one. The original controller didn't take the discretization
period into account. To fix this, teams should just have to divide their
Ki gain by 0.05 and multiply their Kd gain by 0.05 where 0.05 is the
original default period.

wpilibc/src/test/native/cpp/PIDInputOutputTest.cpp

@@ -0,0 +1,70 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2014-2019 FIRST. All Rights Reserved.                        */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#include "frc/controller/PIDController.h"
+#include "gtest/gtest.h"
+
+class PIDInputOutputTest : public testing::Test {
+ protected:
+  frc2::PIDController* controller;
+
+  void SetUp() override { controller = new frc2::PIDController(0, 0, 0); }
+
+  void TearDown() override { delete controller; }
+};
+
+TEST_F(PIDInputOutputTest, OutputRangeTest) {
+  controller->SetP(1);
+  controller->SetOutputRange(-50, 50);
+
+  EXPECT_DOUBLE_EQ(-50, controller->Calculate(100, 0));
+  EXPECT_DOUBLE_EQ(50, controller->Calculate(0, 100));
+}
+
+TEST_F(PIDInputOutputTest, InputRangeTest) {
+  controller->SetP(1);
+  controller->SetOutputRange(-1000, 1000);
+  controller->SetInputRange(-50, 50);
+
+  EXPECT_DOUBLE_EQ(-100, controller->Calculate(100, 0));
+  EXPECT_DOUBLE_EQ(50, controller->Calculate(0, 100));
+}
+
+TEST_F(PIDInputOutputTest, ContinuousInputTest) {
+  controller->SetP(1);
+  controller->SetInputRange(-180, 180);
+  controller->SetContinuous(true);
+
+  EXPECT_TRUE(controller->Calculate(-179, 179) < 0);
+}
+
+TEST_F(PIDInputOutputTest, ProportionalGainOutputTest) {
+  controller->SetP(4);
+
+  EXPECT_DOUBLE_EQ(-.1, controller->Calculate(.025, 0));
+}
+
+TEST_F(PIDInputOutputTest, IntegralGainOutputTest) {
+  controller->SetI(4);
+
+  double out = 0;
+
+  for (int i = 0; i < 5; i++) {
+    out = controller->Calculate(.025, 0);
+  }
+
+  EXPECT_DOUBLE_EQ(-.5 * controller->GetPeriod(), out);
+}
+
+TEST_F(PIDInputOutputTest, DerivativeGainOutputTest) {
+  controller->SetD(4);
+
+  controller->Calculate(0, 0);
+
+  EXPECT_DOUBLE_EQ(-.01 / controller->GetPeriod(),
+                   controller->Calculate(.0025, 0));
+}

wpilibc/src/test/native/cpp/PIDToleranceTest.cpp

@@ -0,0 +1,111 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2014-2019 FIRST. All Rights Reserved.                        */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#include "frc/Timer.h"
+#include "frc/controller/PIDController.h"
+#include "frc/controller/PIDControllerRunner.h"
+#include "gtest/gtest.h"
+
+using namespace frc;
+
+class PIDToleranceTest : public testing::Test {
+ protected:
+  const double setpoint = 50.0;
+  const double range = 200;
+  const double tolerance = 10.0;
+
+  class FakeInput {
+   public:
+    double val = 0;
+
+    double Get() { return val; }
+  };
+
+  class FakeOutput {
+   public:
+    void Set(double output) {}
+  };
+
+  FakeInput inp;
+  FakeOutput out;
+  frc2::PIDController* pidController;
+  frc::PIDControllerRunner* pidRunner;
+
+  void SetUp() override {
+    pidController = new frc2::PIDController(0.5, 0.0, 0.0);
+    pidController->SetInputRange(-range / 2, range / 2);
+    pidRunner =
+        new frc::PIDControllerRunner(*pidController, [&] { return inp.Get(); },
+                                     [&](double output) { out.Set(output); });
+  }
+
+  void TearDown() override {
+    delete pidRunner;
+    delete pidController;
+  }
+
+  void Reset() { inp.val = 0; }
+};
+
+TEST_F(PIDToleranceTest, Initial) { EXPECT_FALSE(pidController->AtSetpoint()); }
+
+TEST_F(PIDToleranceTest, Absolute) {
+  Reset();
+
+  pidController->SetAbsoluteTolerance(tolerance);
+  pidController->SetSetpoint(setpoint);
+  pidRunner->Enable();
+
+  EXPECT_FALSE(pidController->AtSetpoint())
+      << "Error was in tolerance when it should not have been. Error was "
+      << pidController->GetError();
+
+  inp.val = setpoint + tolerance / 2;
+  Wait(1.0);
+
+  EXPECT_TRUE(pidController->AtSetpoint())
+      << "Error was not in tolerance when it should have been. Error was "
+      << pidController->GetError();
+
+  inp.val = setpoint + 10 * tolerance;
+  Wait(1.0);
+
+  EXPECT_FALSE(pidController->AtSetpoint())
+      << "Error was in tolerance when it should not have been. Error was "
+      << pidController->GetError();
+}
+
+TEST_F(PIDToleranceTest, Percent) {
+  Reset();
+
+  pidController->SetPercentTolerance(tolerance);
+  pidController->SetSetpoint(setpoint);
+  pidRunner->Enable();
+
+  EXPECT_FALSE(pidController->AtSetpoint())
+      << "Error was in tolerance when it should not have been. Error was "
+      << pidController->GetError();
+
+  inp.val =
+      setpoint + (tolerance) / 200 *
+                     range;  // half of percent tolerance away from setpoint
+  Wait(1.0);
+
+  EXPECT_TRUE(pidController->AtSetpoint())
+      << "Error was not in tolerance when it should have been. Error was "
+      << pidController->GetError();
+
+  inp.val =
+      setpoint +
+      (tolerance) / 50 * range;  // double percent tolerance away from setPoint
+
+  Wait(1.0);
+
+  EXPECT_FALSE(pidController->AtSetpoint())
+      << "Error was in tolerance when it should not have been. Error was "
+      << pidController->GetError();
+}