[linux] Add support for simple xselection pasting

02 May 2016 - Don't create an additional window and also don't use
XNextEvent, we already have XNextEvent a different location.
Wait for event SelectionNotify at most for 200 ms and use function
XCheckTypedWindowEvent to check it.

First version: Matthias Kortstiege <mkortstiege@kodi.tv> 4 Jul 2015
https://github.com/mkortstiege/xbmc/tree/linux-paste
mkortstiege@62e56b7

xbmc/windowing/X11/WinSystemX11.cpp

@@ -48,6 +48,8 @@
 
 using namespace KODI::MESSAGING;
 
+#include <limits.h>
+
 #define EGL_NO_CONFIG (EGLConfig)0
 
 CWinSystemX11::CWinSystemX11() : CWinSystemBase()
@@ -1070,4 +1072,53 @@ void CWinSystemX11::UpdateCrtc()
   g_graphicsContext.SetFPS(fps);
 }
 
+std::string CWinSystemX11::GetClipboardText(void)
+{
+  if (!m_dpy)
+     return "";
+
+  std::string result;
+  Atom utf8_string = XInternAtom(m_dpy, "UTF8_STRING", False);
+  Atom clipboard = XInternAtom(m_dpy, "CLIPBOARD", False);
+  XConvertSelection(m_dpy, clipboard, utf8_string, None, m_glWindow, CurrentTime);
+//  Wait for clipboard event (SelectionNotify) sync, code copied from 
+//  https://github.com/vinniefalco/SimpleDJ/blob/master/Extern/JUCE/modules/juce_gui_basics/native/juce_linux_Clipboard.cpp
+  int count = 20; // will wait at most for 200 ms
+  while (--count >= 0)
+  {
+    XEvent event;
+    if (XCheckTypedWindowEvent (m_dpy, m_glWindow, SelectionNotify, &event))
+      break;
+    // not very elegant.. we could do a select() or something like that...
+    // however clipboard content requesting is inherently slow on x11, it
+    // often takes 50ms or more so...
+    Sleep(10);
+  }
+
+  for(unsigned long offset = 0;;)
+  {
+    Atom real_type = None;
+    unsigned char *data;
+    unsigned long items_read, items_left = 0;
+    int real_format = 0;
+
+    Atom utf8_string = XInternAtom(m_dpy, "UTF8_STRING", False);
+    XGetWindowProperty(m_dpy, m_glWindow, utf8_string, offset, INT_MAX, False,
+      AnyPropertyType, &real_type, &real_format, &items_read, &items_left, &data);
+
+    if(items_read)
+    {
+      result.append(reinterpret_cast<const char*>(data), items_read);
+      offset += items_read;
+    }
+
+    XDeleteProperty(m_dpy, m_glWindow, utf8_string);
+
+    if(!items_left)
+      break;
+  }
+
+  return result;
+}
+
 #endif

xbmc/windowing/X11/WinSystemX11.h

@@ -68,6 +68,7 @@ class CWinSystemX11 : public CWinSystemBase
   bool IsCurrentOutput(std::string output);
   void RecreateWindow();
   int GetCrtc() { return m_crtc; }
+  std::string GetClipboardText(void);
 
 protected:
   virtual bool SetWindow(int width, int height, bool fullscreen, const std::string &output, int *winstate = NULL) = 0;