CameraServer: auto-increment startAutomaticCapture(). (#468)

Also add GetServer() functions so the automatically created VideoSink can
be retrieved by user code if desired.

wpilibc/athena/include/CameraServer.h

@@ -7,6 +7,7 @@
 
 #pragma once
 
+#include <atomic>
 #include <memory>
 #include <mutex>
 #include <string>
@@ -44,8 +45,10 @@ class CameraServer : public ErrorBase {
    * If you also want to perform vision processing on the roboRIO, use
    * getVideo() to get access to the camera images.
    *
-   * This overload calls {@link #StartAutomaticCapture(int)} with device 0,
-   * creating a camera named "USB Camera 0".
+   * The first time this overload is called, it calls
+   * {@link #StartAutomaticCapture(int)} with device 0, creating a camera
+   * named "USB Camera 0".  Subsequent calls increment the device number
+   * (e.g. 1, 2, etc).
    */
   cs::UsbCamera StartAutomaticCapture();
 
@@ -241,6 +244,21 @@ class CameraServer : public ErrorBase {
    */
   void RemoveServer(llvm::StringRef name);
 
+  /**
+   * Get server for the primary camera feed.
+   *
+   * <p>This is only valid to call after a camera feed has been added
+   * with StartAutomaticCapture() or AddServer().
+   */
+  cs::VideoSink GetServer();
+
+  /**
+   * Gets a server by name.
+   *
+   * @param name Server name
+   */
+  cs::VideoSink GetServer(llvm::StringRef name);
+
   /**
    * Adds an already created camera.
    *
@@ -277,6 +295,7 @@ class CameraServer : public ErrorBase {
   static constexpr char const* kPublishName = "/CameraPublisher";
 
   std::mutex m_mutex;
+  std::atomic<int> m_defaultUsbDevice;
   std::string m_primarySourceName;
   llvm::StringMap<cs::VideoSource> m_sources;
   llvm::StringMap<cs::VideoSink> m_sinks;

wpilibc/athena/src/CameraServer.cpp

@@ -486,7 +486,7 @@ CameraServer::CameraServer()
 }
 
 cs::UsbCamera CameraServer::StartAutomaticCapture() {
-  return StartAutomaticCapture(0);
+  return StartAutomaticCapture(m_defaultUsbDevice++);
 }
 
 cs::UsbCamera CameraServer::StartAutomaticCapture(int dev) {
@@ -659,6 +659,33 @@ void CameraServer::RemoveServer(llvm::StringRef name) {
   m_sinks.erase(name);
 }
 
+cs::VideoSink CameraServer::GetServer() {
+  llvm::SmallString<64> name;
+  {
+    std::lock_guard<std::mutex> lock(m_mutex);
+    if (m_primarySourceName.empty()) {
+      wpi_setWPIErrorWithContext(CameraServerError, "no camera available");
+      return cs::VideoSink{};
+    }
+    name = "serve_";
+    name += m_primarySourceName;
+  }
+  return GetServer(name);
+}
+
+cs::VideoSink CameraServer::GetServer(llvm::StringRef name) {
+  std::lock_guard<std::mutex> lock(m_mutex);
+  auto it = m_sinks.find(name);
+  if (it == m_sinks.end()) {
+    llvm::SmallString<64> buf;
+    llvm::raw_svector_ostream err{buf};
+    err << "could not find server " << name;
+    wpi_setWPIErrorWithContext(CameraServerError, err.str());
+    return cs::VideoSink{};
+  }
+  return it->second;
+}
+
 void CameraServer::AddCamera(const cs::VideoSource& camera) {
   std::string name = camera.GetName();
   std::lock_guard<std::mutex> lock(m_mutex);

wpilibj/src/athena/java/edu/wpi/first/wpilibj/CameraServer.java

@@ -24,6 +24,7 @@ import edu.wpi.cscore.VideoSource;
 import edu.wpi.first.wpilibj.networktables.NetworkTable;
 import edu.wpi.first.wpilibj.networktables.NetworkTablesJNI;
 import edu.wpi.first.wpilibj.tables.ITable;
+import java.util.concurrent.atomic.AtomicInteger;
 import java.util.ArrayList;
 import java.util.Hashtable;
 import java.util.regex.Matcher;
@@ -56,6 +57,7 @@ public class CameraServer {
     return server;
   }
 
+  private AtomicInteger m_defaultUsbDevice;
   private String m_primarySourceName;
   private final Hashtable<String, VideoSource> m_sources;
   private final Hashtable<String, VideoSink> m_sinks;
@@ -330,6 +332,7 @@ public class CameraServer {
 
   @SuppressWarnings({"JavadocMethod", "PMD.UnusedLocalVariable"})
   private CameraServer() {
+    m_defaultUsbDevice = new AtomicInteger();
     m_sources = new Hashtable<String, VideoSource>();
     m_sinks = new Hashtable<String, VideoSink>();
     m_tables = new Hashtable<Integer, ITable>();
@@ -513,11 +516,13 @@ public class CameraServer {
    * If you also want to perform vision processing on the roboRIO, use
    * getVideo() to get access to the camera images.
    *
-   * <p>This overload calls {@link #startAutomaticCapture(int)} with device 0,
-   * creating a camera named "USB Camera 0".
+   * <p>The first time this overload is called, it calls
+   * {@link #startAutomaticCapture(int)} with device 0, creating a camera
+   * named "USB Camera 0".  Subsequent calls increment the device number
+   * (e.g. 1, 2, etc).
    */
   public UsbCamera startAutomaticCapture() {
-    return startAutomaticCapture(0);
+    return startAutomaticCapture(m_defaultUsbDevice.getAndIncrement());
   }
 
   /**
@@ -745,6 +750,32 @@ public class CameraServer {
     }
   }
 
+  /**
+   * Get server for the primary camera feed.
+   *
+   * <p>This is only valid to call after a camera feed has been added
+   * with startAutomaticCapture() or addServer().
+   */
+  public VideoSink getServer() {
+    synchronized (this) {
+      if (m_primarySourceName == null) {
+        throw new VideoException("no camera available");
+      }
+      return getServer("serve_" + m_primarySourceName);
+    }
+  }
+
+  /**
+   * Gets a server by name.
+   *
+   * @param name Server name
+   */
+  public VideoSink getServer(String name) {
+    synchronized (this) {
+      return m_sinks.get(name);
+    }
+  }
+
   /**
    * Adds an already created camera.
    *