Add NT controlled framerate limiter (#2257)

Adds a method to lower the speed of a pipeline over NT, primarily to
reduce power consumption.

photon-lib/src/main/java/org/photonvision/PhotonCamera.java

@@ -66,6 +66,8 @@ public class PhotonCamera implements AutoCloseable {
     PacketSubscriber<PhotonPipelineResult> resultSubscriber;
     BooleanPublisher driverModePublisher;
     BooleanSubscriber driverModeSubscriber;
+    IntegerPublisher fpsLimitPublisher;
+    IntegerSubscriber fpsLimitSubscriber;
     StringSubscriber versionEntry;
     IntegerEntry inputSaveImgEntry, outputSaveImgEntry;
     IntegerPublisher pipelineIndexRequest, ledModeRequest;
@@ -81,6 +83,8 @@ public class PhotonCamera implements AutoCloseable {
         resultSubscriber.close();
         driverModePublisher.close();
         driverModeSubscriber.close();
+        fpsLimitPublisher.close();
+        fpsLimitSubscriber.close();
         versionEntry.close();
         inputSaveImgEntry.close();
         outputSaveImgEntry.close();
@@ -144,6 +148,8 @@ public class PhotonCamera implements AutoCloseable {
         resultSubscriber = new PacketSubscriber<>(rawBytesEntry, PhotonPipelineResult.photonStruct);
         driverModePublisher = cameraTable.getBooleanTopic("driverModeRequest").publish();
         driverModeSubscriber = cameraTable.getBooleanTopic("driverMode").subscribe(false);
+        fpsLimitPublisher = cameraTable.getIntegerTopic("fpsLimitRequest").publish();
+        fpsLimitSubscriber = cameraTable.getIntegerTopic("fpsLimit").subscribe(-1);
         inputSaveImgEntry = cameraTable.getIntegerTopic("inputSaveImgCmd").getEntry(0);
         outputSaveImgEntry = cameraTable.getIntegerTopic("outputSaveImgCmd").getEntry(0);
         pipelineIndexRequest = cameraTable.getIntegerTopic("pipelineIndexRequest").publish();
@@ -373,6 +379,24 @@ public class PhotonCamera implements AutoCloseable {
         driverModePublisher.set(driverMode);
     }
 
+    /**
+     * Gets the FPS limit set on the camera.
+     *
+     * @return The current FPS limit.
+     */
+    public int getFPSLimit() {
+        return (int) fpsLimitSubscriber.get();
+    }
+
+    /**
+     * Sets the FPS limit on the camera.
+     *
+     * @param fps The FPS limit to set. Set to -1 for unlimited FPS.
+     */
+    public void setFPSLimit(int fps) {
+        fpsLimitPublisher.set(fps);
+    }
+
     /**
      * Request the camera to save a new image file from the input camera stream with overlays. Images
      * take up space in the filesystem of the PhotonCamera. Calling it frequently will fill up disk

photon-lib/src/main/native/cpp/photon/PhotonCamera.cpp

@@ -196,6 +196,9 @@ PhotonCamera::PhotonCamera(nt::NetworkTableInstance instance,
           rootTable->GetBooleanTopic("driverMode").Subscribe(false)),
       driverModePublisher(
           rootTable->GetBooleanTopic("driverModeRequest").Publish()),
+      fpsLimitSubscriber(rootTable->GetIntegerTopic("fpsLimit").Subscribe(-1)),
+      fpsLimitPublisher(
+          rootTable->GetIntegerTopic("fpsLimitRequest").Publish()),
       heartbeatSubscriber(
           rootTable->GetIntegerTopic("heartbeat").Subscribe(-1)),
       topicNameSubscriber(instance, PHOTON_PREFIX, {.topicsOnly = true}),
@@ -322,6 +325,14 @@ void PhotonCamera::SetDriverMode(bool driverMode) {
   driverModePublisher.Set(driverMode);
 }
 
+bool PhotonCamera::GetDriverMode() const { return driverModeSubscriber.Get(); }
+
+int PhotonCamera::GetFPSLimit() const { return fpsLimitSubscriber.Get(); }
+
+void PhotonCamera::SetFPSLimit(int fpsLimit) {
+  fpsLimitPublisher.Set(fpsLimit);
+}
+
 void PhotonCamera::TakeInputSnapshot() {
   inputSaveImgEntry.Set(inputSaveImgSubscriber.Get() + 1);
 }
@@ -330,8 +341,6 @@ void PhotonCamera::TakeOutputSnapshot() {
   outputSaveImgEntry.Set(outputSaveImgSubscriber.Get() + 1);
 }
 
-bool PhotonCamera::GetDriverMode() const { return driverModeSubscriber.Get(); }
-
 void PhotonCamera::SetPipelineIndex(int index) { pipelineIndexPub.Set(index); }
 
 int PhotonCamera::GetPipelineIndex() const {

photon-lib/src/main/native/include/photon/PhotonCamera.h

@@ -103,6 +103,16 @@ class PhotonCamera {
    */
   bool GetDriverMode() const;
 
+  /**
+   * @param fpsLimit The FPS limit to set. Use -1 for unlimited FPS.
+   */
+  void SetFPSLimit(int fpsLimit);
+
+  /**
+   * @return The FPS limit set on the camera, or -1 if no limit is set.
+   */
+  int GetFPSLimit() const;
+
   /**
    * Request the camera to save a new image file from the input
    * camera stream with overlays.
@@ -210,6 +220,9 @@ class PhotonCamera {
 
   nt::BooleanSubscriber driverModeSubscriber;
   nt::BooleanPublisher driverModePublisher;
+  nt::IntegerSubscriber fpsLimitSubscriber;
+  nt::IntegerPublisher fpsLimitPublisher;
+
   nt::IntegerSubscriber ledModeSubscriber;
 
   nt::IntegerSubscriber heartbeatSubscriber;