Add rich clipboard support

This implements a more powerful protocol for working with clipboards, which
supports datatype negotiation, and fixes various issues by mapping more
directly to how things work on X11.

3 files changed, 121 insertions, 1 deletions

diff --git a/doc/c/clipboards.rst b/doc/c/clipboards.rst
new file mode 100644
index 0000000..ec66bd5
--- /dev/null
+++ b/doc/c/clipboards.rst
@@ -0,0 +1,118 @@
+.. default-domain:: c
+.. highlight:: c
+
+################
+Using Clipboards
+################
+
+Clipboards provide a way to transfer data between different views,
+including views in different processes.
+A clipboard transfer is a multi-step event-driven process,
+where the sender and receiver can negotiate a mutually supported data format.
+
+*******
+Copying
+*******
+
+Data can be copied to the general clipboard with :func:`puglSetClipboard`.
+The `MIME type <https://www.iana.org/assignments/media-types/media-types.xhtml>`_ of the data must be specified.
+Commonly supported types are ``text/plain`` for plain text,
+and `text/uri-list <http://amundsen.com/hypermedia/urilist/>`_ for lists of URIs (including local files).
+
+For example, a string can be copied to the clipboard by setting the general clipboard to ``text/plain`` data:
+
+.. code-block:: c
+
+   const char* someString = "Copied string";
+
+   puglSetClipboard(view,
+                    "text/plain",
+                    someString,
+                    strlen(someString));
+
+*******
+Pasting
+*******
+
+Data from a clipboard can be pasted to a view using :func:`puglPaste`:
+
+.. code-block:: c
+
+   puglPaste(view);
+
+This initiates a data transfer from the clipboard to the view if possible.
+If data is available,
+the view will be sent a :enumerator:`PUGL_DATA_OFFER` event to begin the transfer.
+
+**************
+Receiving Data
+**************
+
+A data transfer from a clipboard to a view begins with the view receiving a :enumerator:`PUGL_DATA_OFFER` event.
+This indicates that data (possibly in several formats) is being offered to a view,
+which can either "accept" or "reject" it:
+
+.. code-block:: c
+
+   case PUGL_DATA_OFFER:
+     onDataOffer(view, &event->offer);
+     break;
+
+When handling this event,
+:func:`puglGetNumClipboardTypes` and :func:`puglGetClipboardType` can be used to enumerate the available data types:
+
+.. code-block:: c
+
+   static void
+   onDataOffer(PuglView* view, const PuglEventDataOffer* event)
+   {
+     size_t numTypes = puglGetNumClipboardTypes(view, clipboard);
+
+     for (uint32_t t = 0; t < numTypes; ++t) {
+       const char* type = puglGetClipboardType(view, t);
+       printf("Offered type: %s\n", type);
+     }
+   }
+
+If the view supports one of the data types,
+it can accept the offer with :func:`puglAcceptOffer`:
+
+.. code-block:: c
+
+   for (uint32_t t = 0; t < numTypes; ++t) {
+     const char* type = puglGetClipboardType(view, t);
+     if (!strcmp(type, "text/uri-list")) {
+       puglAcceptOffer(view, event, t);
+     }
+   }
+
+When an offer is accepted,
+the data will be transferred and converted if necessary,
+then the view will be sent a :enumerator:`PUGL_DATA` event.
+When the data event is received,
+the data can be fetched with :func:`puglGetClipboard`:
+
+.. code-block:: c
+
+   case PUGL_DATA:
+     onData(view, &event->data);
+     break;
+
+   // ...
+
+   static void
+   onData(PuglView* view, const PuglEventData* event)
+   {
+     uint32_t typeIndex = event->typeIndex;
+
+     const char* type = puglGetClipboardType(view, typeIndex);
+
+     fprintf(stderr, "Received data type: %s\n", type);
+
+     if (!strcmp(type, "text/plain")) {
+       size_t      len  = 0;
+       const void* data = puglGetClipboard(view, typeIndex, &len);
+
+       printf("Dropped: %s\n", (const char*)data);
+     }
+   }
diff --git a/doc/c/meson.build b/doc/c/meson.build
index 8592f75..f8b4626 100644
--- a/doc/c/meson.build
+++ b/doc/c/meson.build
@@ -1,4 +1,4 @@
-# Copyright 2021 David Robillard <d@drobilla.net>
+# Copyright 2021-2022 David Robillard <d@drobilla.net>
 # SPDX-License-Identifier: CC0-1.0 OR ISC
 
 config = configuration_data()
@@ -18,6 +18,7 @@ c_rst_files = files(
   'view.rst',
   'events.rst',
   'event-loop.rst',
+  'clipboards.rst',
   'shutting-down.rst'
 )
 
diff --git a/doc/c/overview.rst b/doc/c/overview.rst
index 4bd024d..2bab700 100644
--- a/doc/c/overview.rst
+++ b/doc/c/overview.rst
@@ -21,6 +21,7 @@ The core API (excluding backend-specific components) is declared in ``pugl.h``:
    view
    events
    event-loop
+   clipboards
    shutting-down
 
 .. _pkg-config: https://www.freedesktop.org/wiki/Software/pkg-config/