plugin: Add clapper GStreamer plugin

Add new GStreamer plugin that consists of multiple elements for Clapper video player.

The main difference is that unlike the old one, this does not operate using `GtkGLArea`
anymore, but processes and displays `GdkTextures` directly through `GtkPicture` widget.
Also this one is installed like any other GStreamer plugin, thus can be used via
`gst-launch-1.0` binary or even used by other GTK4 apps if they wish to integrate it.

This commit adds new video sink that uses a new kind of memory as input, called
`ClapperGdkMemory`. With it comes a simple dedicated memory allocator, buffer pool
and a `clapperimport` element that converts system mapped memory frames into
`GdkTextures` that are later passed in our `ClapperGdkMemory` for the sink to display.

lib/gst/plugin/gstclappergdkmemory.c

@@ -0,0 +1,141 @@
+/*
+ * Copyright (C) 2022 Rafał Dzięgiel <rafostar.github@gmail.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Library General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include "gstclappergdkmemory.h"
+#include "gstgtkutils.h"
+
+#define GST_CAT_DEFAULT gst_clapper_gdk_allocator_debug
+GST_DEBUG_CATEGORY_STATIC (GST_CAT_DEFAULT);
+
+static GstAllocator *_gst_clapper_gdk_allocator = NULL;
+
+#define parent_class gst_clapper_gdk_allocator_parent_class
+G_DEFINE_TYPE (GstClapperGdkAllocator, gst_clapper_gdk_allocator, GST_TYPE_ALLOCATOR);
+
+static void
+gst_clapper_gdk_allocator_free (GstAllocator *self, GstMemory *memory)
+{
+  GstClapperGdkMemory *mem = GST_CLAPPER_GDK_MEMORY_CAST (memory);
+
+  GST_TRACE_OBJECT (self, "Freeing ClapperGdkMemory: %" GST_PTR_FORMAT, mem);
+
+  g_clear_object (&mem->texture);
+  g_free (mem);
+}
+
+static gpointer
+gst_clapper_gdk_mem_map_full (GstMemory *memory, GstMapInfo *info, gsize maxsize)
+{
+  GstClapperGdkMemory *mem = GST_CLAPPER_GDK_MEMORY_CAST (memory);
+
+  return &mem->texture;
+}
+
+static void
+gst_clapper_gdk_mem_unmap_full (GstMemory *memory, GstMapInfo *info)
+{
+  /* NOOP */
+}
+
+static GstMemory *
+gst_clapper_gdk_mem_copy (GstMemory *memory, gssize offset, gssize size)
+{
+  return NULL;
+}
+
+static GstMemory *
+gst_clapper_gdk_mem_share (GstMemory *memory, gssize offset, gssize size)
+{
+  return NULL;
+}
+
+static gboolean
+gst_clapper_gdk_mem_is_span (GstMemory *mem1, GstMemory *mem2, gsize *offset)
+{
+  return FALSE;
+}
+
+static void
+gst_clapper_gdk_allocator_init (GstClapperGdkAllocator *self)
+{
+  GstAllocator *alloc = GST_ALLOCATOR_CAST (self);
+
+  alloc->mem_type = GST_CLAPPER_GDK_MEMORY_TYPE_NAME;
+  alloc->mem_map_full = gst_clapper_gdk_mem_map_full;
+  alloc->mem_unmap_full = gst_clapper_gdk_mem_unmap_full;
+  alloc->mem_copy = gst_clapper_gdk_mem_copy;
+  alloc->mem_share = gst_clapper_gdk_mem_share;
+  alloc->mem_is_span = gst_clapper_gdk_mem_is_span;
+
+  GST_OBJECT_FLAG_SET (self, GST_ALLOCATOR_FLAG_CUSTOM_ALLOC);
+}
+
+static void
+gst_clapper_gdk_allocator_class_init (GstClapperGdkAllocatorClass *klass)
+{
+  GstAllocatorClass *allocator_class = (GstAllocatorClass *) klass;
+
+  allocator_class->alloc = NULL;
+  allocator_class->free = GST_DEBUG_FUNCPTR (gst_clapper_gdk_allocator_free);
+
+  GST_DEBUG_CATEGORY_INIT (GST_CAT_DEFAULT, "clappergdkallocator", 0,
+      "Clapper Gdk Allocator");
+}
+
+void
+gst_clapper_gdk_memory_init_once (void)
+{
+  static gsize _alloc_init = 0;
+
+  if (g_once_init_enter (&_alloc_init)) {
+    _gst_clapper_gdk_allocator = GST_ALLOCATOR_CAST (
+        g_object_new (GST_TYPE_CLAPPER_GDK_ALLOCATOR, NULL));
+    gst_object_ref_sink (_gst_clapper_gdk_allocator);
+
+    gst_allocator_register (GST_CLAPPER_GDK_MEMORY_TYPE_NAME, _gst_clapper_gdk_allocator);
+    g_once_init_leave (&_alloc_init, 1);
+  }
+}
+
+gboolean
+gst_is_clapper_gdk_memory (GstMemory *memory)
+{
+  return (memory != NULL && memory->allocator != NULL
+      && GST_IS_CLAPPER_GDK_ALLOCATOR (memory->allocator));
+}
+
+GstMemory *
+gst_clapper_gdk_allocator_alloc (GstClapperGdkAllocator *self, const GstVideoInfo *info)
+{
+  GstClapperGdkMemory *mem;
+
+  mem = g_new0 (GstClapperGdkMemory, 1);
+  mem->info = *info;
+
+  gst_memory_init (GST_MEMORY_CAST (mem), 0, GST_ALLOCATOR_CAST (self),
+      NULL, GST_VIDEO_INFO_SIZE (info), 0, 0, GST_VIDEO_INFO_SIZE (info));
+
+  GST_TRACE_OBJECT (self, "Allocated new ClapperGdkMemory: %" GST_PTR_FORMAT, mem);
+
+  return GST_MEMORY_CAST (mem);
+}