Add support for USB Webcams on Windows (#1390)

cscore/src/main/native/windows/WindowsMessagePump.h

@@ -0,0 +1,66 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2018 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.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#pragma once
+
+#include <windows.h>
+
+#include <functional>
+#include <thread>
+
+namespace cs {
+class WindowsMessagePump {
+ public:
+  WindowsMessagePump(
+      std::function<LRESULT(HWND, UINT, WPARAM, LPARAM)> callback);
+  ~WindowsMessagePump();
+
+  friend LRESULT CALLBACK pWndProc(HWND hwnd, UINT uiMsg, WPARAM wParam,
+                                   LPARAM lParam);
+
+  template <typename RetVal = LRESULT, typename FirstParam = WPARAM,
+            typename SecondParam = LPARAM>
+  RetVal SendWindowMessage(UINT msg, FirstParam wParam, SecondParam lParam) {
+    static_assert(sizeof(FirstParam) <= sizeof(WPARAM),
+                  "First Parameter Does Not Fit");
+    static_assert(sizeof(SecondParam) <= sizeof(LPARAM),
+                  "Second Parameter Does Not Fit");
+    static_assert(sizeof(RetVal) <= sizeof(LRESULT),
+                  "Return Value Does Not Fit");
+    WPARAM firstToSend = 0;
+    LPARAM secondToSend = 0;
+    std::memcpy(&firstToSend, &wParam, sizeof(FirstParam));
+    std::memcpy(&secondToSend, &lParam, sizeof(SecondParam));
+    LRESULT result = SendMessage(hwnd, msg, firstToSend, secondToSend);
+    RetVal toReturn;
+    std::memset(&toReturn, 0, sizeof(RetVal));
+    std::memcpy(&toReturn, &result, sizeof(RetVal));
+    return toReturn;
+  }
+
+  template <typename FirstParam = WPARAM, typename SecondParam = LPARAM>
+  BOOL PostWindowMessage(UINT msg, FirstParam wParam, SecondParam lParam) {
+    static_assert(sizeof(FirstParam) <= sizeof(WPARAM),
+                  "First Parameter Does Not Fit");
+    static_assert(sizeof(SecondParam) <= sizeof(LPARAM),
+                  "Second Parameter Does Not Fit");
+    WPARAM firstToSend = 0;
+    LPARAM secondToSend = 0;
+    std::memcpy(&firstToSend, &wParam, sizeof(FirstParam));
+    std::memcpy(&secondToSend, &lParam, sizeof(SecondParam));
+    return PostMessage(hwnd, msg, firstToSend, secondToSend);
+  }
+
+ private:
+  void ThreadMain(HANDLE eventHandle);
+
+  HWND hwnd;
+  std::function<LRESULT(HWND, UINT, WPARAM, LPARAM)> m_callback;
+
+  std::thread m_mainThread;
+};
+}  // namespace cs