implement clipboard on iOS

PanoPainter/GameViewController.h

@@ -35,4 +35,6 @@
 - (void)share_file:(NSString*)file_path;
 - (void)tick;
 - (void)render_loop;
+- (std::string)clipboard_get_string;
+- (bool)clipboard_set_string:(const std::string&)s;
 @end

PanoPainter/GameViewController.m

@@ -44,6 +44,18 @@ NSThread* lock_thread;
 std::recursive_mutex lock_mutex;
 
 @implementation GameViewController
+- (std::string)clipboard_get_string
+{
+    NSString* ns = [[UIPasteboard generalPasteboard] string];
+    const char* ptr = [ns cStringUsingEncoding:NSUTF8StringEncoding];
+    return std::string(ptr);
+}
+- (bool)clipboard_set_string:(const std::string &)s
+{
+    NSString* ns = [NSString stringWithUTF8String:s.c_str()];
+    [[UIPasteboard generalPasteboard] setString:ns];
+    return true;
+}
 - (void)crash
 {
     AppDelegate* app = (AppDelegate*)[[UIApplication sharedApplication] delegate];