DnD of filenames: make Wayland behave as Windows and macOS

and also add more detailed documentation of platform-specific behaviors.

documentation/src/events.dox

@@ -268,16 +268,7 @@ selection indication. Most modern programs ignore this.
 
 FLTK supports drag and drop of text and files from any
 application on the desktop to an FLTK widget. Text is transferred
-using UTF-8 encoding. Files are received as a list of full path
-and file names, separated by newline.
-
-On some X11 platforms and with Wayland, files are received as a URL-encoded UTF-8 string,
-that is, non-ASCII bytes (and a few others such as space and %) are
-replaced by the 3 bytes "%XY" where XY are the byte's hexadecimal value.
-The \ref fl_decode_uri() function can be used to transform in-place
-the received string into a proper UTF-8 string. On these platforms,
-strings corresponding to dropped files are further prepended
-by <tt>file://</tt> (or other prefixes such as <tt>computer://</tt>).
+using UTF-8 encoding.
 
 See Fl::dnd() for drag and drop from an FLTK widget.
 
@@ -290,6 +281,20 @@ depends on the protocol used on each platform.
 \p FL_DND_* events cannot be used in widgets derived
 from Fl_Group or Fl_Window.
 
+\subsection events_fl_dnd_files Dropped filenames
+Files are received as a list of full path and file names.
+- On some X11 platforms, files are received as a URL-encoded UTF-8 string,
+that is, non-ASCII bytes (and a few others such as space and %) are
+replaced by the 3 bytes "%XY" where XY are the byte's hexadecimal value.
+The \ref fl_decode_uri() function can be used to transform in-place
+the received string into a proper UTF-8 string. On these platforms,
+strings corresponding to dropped files are further prepended
+by <tt>file://</tt> (or other prefixes such as <tt>computer://</tt>).
+- Other X11 situations put all dropped filenames in a single line, separated by
+spaces.
+- On non-X11 platforms, including Wayland, files dropped are received one
+pathname per line, with no  <tt>'\\n'</tt> after the last pathname.
+
 \subsection events_fl_dnd_enter FL_DND_ENTER
 
 The mouse has been moved to point at this widget. A widget that is

documentation/src/wayland.dox

@@ -763,8 +763,7 @@ FLTK can copy or paste plain UTF-8 text or image data to/from the clipboard. Ima
 clipboard as \c image/bmp mime type. Images in \c image/bmp or \c image/png mime types from the
 clipboard can be pasted to FLTK apps.
 
-Files dropped are received one per line with URL-encoded UTF-8 names prepended by
-<tt>file://</tt> (see \ref events_dnd).
+Files dropped are received one pathname per line, with no '\n' after the last pathname.
 
 
 \section wayland-egl EGL as support for OpenGL

src/drivers/Wayland/fl_wayland_clipboard_dnd.cxx

@@ -328,6 +328,7 @@ static void data_device_handle_selection(void *data, struct wl_data_device *data
 // which is enlarged if necessary.
 static void get_clipboard_or_dragged_text(struct wl_data_offer *offer) {
   int fds[2];
+  char *from;
   if (pipe(fds)) return;
   wl_data_offer_receive(offer, fl_selection_offer_type, fds[1]);
   close(fds[1]);
@@ -341,7 +342,7 @@ static void get_clipboard_or_dragged_text(struct wl_data_offer *offer) {
       close(fds[0]);
       fl_selection_length[1] = to - fl_selection_buffer[1];
       fl_selection_buffer[1][ fl_selection_length[1] ] = 0;
-      return;
+      goto way_out;
     }
     n = Fl_Screen_Driver::convert_crlf(to, n);
     to += n;
@@ -360,7 +361,7 @@ static void get_clipboard_or_dragged_text(struct wl_data_offer *offer) {
   }
 //fprintf(stderr, "get_clipboard_or_dragged_text: size=%ld\n", rest);
   // read full clipboard data
-  if (pipe(fds)) return;
+  if (pipe(fds)) goto way_out;
   wl_data_offer_receive(offer, fl_selection_offer_type, fds[1]);
   close(fds[1]);
   wl_display_flush(Fl_Wayland_Screen_Driver::wl_display);
@@ -369,7 +370,7 @@ static void get_clipboard_or_dragged_text(struct wl_data_offer *offer) {
     fl_selection_buffer[1] = new char[rest+1000+1];
     fl_selection_buffer_length[1] = rest+1000;
   }
-  char *from = fl_selection_buffer[1];
+  from = fl_selection_buffer[1];
   while (true) {
     ssize_t n = read(fds[0], from, rest);
     if (n <= 0) {
@@ -381,6 +382,19 @@ static void get_clipboard_or_dragged_text(struct wl_data_offer *offer) {
   }
   fl_selection_length[1] = from - fl_selection_buffer[1];
   fl_selection_buffer[1][fl_selection_length[1]] = 0;
+way_out:
+  if (strcmp(fl_selection_offer_type, "text/uri-list") == 0) {
+    fl_decode_uri(fl_selection_buffer[1]); // decode encoded bytes
+    char *p = fl_selection_buffer[1];
+    while (*p) { // remove prefixes
+      if (strncmp(p, "file://", 7) == 0) {
+        memmove(p, p+7, strlen(p+7)+1);
+      }
+      p = strchr(p, '\n');
+      if (!p) break;
+      if (*++p == 0) *(p-1) = 0; // remove last '\n'
+    }
+  }
   Fl::e_clipboard_type = Fl::clipboard_plain_text;
 }