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/meson.build

@@ -1,5 +1,5 @@
 glib_req = '>= 2.56.0'
-gst_req = '>= 1.18.0'
+gst_req = '>= 1.20.0'
 
 api_version = '1.0'
 libversion = meson.project_version()
@@ -132,7 +132,7 @@ cdata.set('SIZEOF_SHORT', cc.sizeof('short'))
 cdata.set('SIZEOF_VOIDP', cc.sizeof('void*'))
 
 cdata.set_quoted('VERSION', libversion)
-cdata.set_quoted('PACKAGE', 'gst-plugins-clapper')
+cdata.set_quoted('PACKAGE', 'clapper')
 cdata.set_quoted('PACKAGE_VERSION', libversion)
 cdata.set_quoted('PACKAGE_BUGREPORT', 'https://github.com/Rafostar/clapper/issues/new')
 cdata.set_quoted('PACKAGE_NAME', 'GStreamer Clapper Libs')
@@ -184,7 +184,7 @@ foreach extra_arg : warning_flags
   endif
 endforeach
 
-cdata.set_quoted('GST_PACKAGE_NAME', 'GStreamer Plugins Clapper')
+cdata.set_quoted('GST_PACKAGE_NAME', 'gst-plugin-clapper')
 cdata.set_quoted('GST_PACKAGE_ORIGIN', 'https://github.com/Rafostar/clapper')
 
 # Mandatory GST deps
@@ -200,6 +200,8 @@ gsttag_dep = dependency('gstreamer-tag-1.0', version: gst_req,
   fallback: ['gst-plugins-base', 'tag_dep'])
 gstvideo_dep = dependency('gstreamer-video-1.0', version: gst_req,
   fallback: ['gst-plugins-base', 'video_dep'])
+gstallocators_dep = dependency('gstreamer-allocators-1.0', version: gst_req,
+  fallback : ['gst-plugins-base', 'allocators_dep'])
 
 # GStreamer OpenGL
 gstgl_dep = dependency('gstreamer-gl-1.0', version: gst_req,
@@ -251,21 +253,49 @@ giounix_dep = dependency('gio-unix-2.0', version: glib_req, fallback: ['glib', '
 
 cdata.set('DISABLE_ORC', 1)
 cdata.set('GST_ENABLE_EXTRA_CHECKS', get_option('devel-checks'))
-cdata.set_quoted('GST_PACKAGE_RELEASE_DATETIME', 'Unknown')
 
 configinc = include_directories('.')
 libsinc = include_directories('gst')
 
-gir = find_program('g-ir-scanner', required: true)
-if not gir.found()
-  error('Clapper requires GI bindings to be compiled')
-endif
-
+gir = find_program('g-ir-scanner')
 gir_init_section = ['--add-init-section=extern void gst_init(gint*,gchar**);' + \
     'g_setenv("GST_REGISTRY_1.0", "@0@", TRUE);'.format(meson.current_build_dir() + '/gir_empty_registry.reg') + \
     'g_setenv("GST_PLUGIN_PATH_1_0", "", TRUE);' + \
     'g_setenv("GST_PLUGIN_SYSTEM_PATH_1_0", "", TRUE);' + \
     'gst_init(NULL,NULL);', '--quiet'
 ]
+
+gtk_deps = [gstgl_dep, gstglproto_dep]
+have_gtk_gl_windowing = false
+
+gtk4_dep = dependency('gtk4', required: true)
+
+if not gtk4_dep.version().version_compare('>=4.0.0')
+  error('GTK4 version on this system is too old')
+endif
+
+if gst_gl_have_window_x11 and (gst_gl_have_platform_egl or gst_gl_have_platform_glx)
+  gtk_x11_dep = dependency('gtk4-x11', required: false)
+  if gtk_x11_dep.found()
+    gtk_deps += gtk_x11_dep
+    if gst_gl_have_platform_glx
+      gtk_deps += gstglx11_dep
+    endif
+    have_gtk_gl_windowing = true
+  endif
+endif
+
+if gst_gl_have_window_wayland and gst_gl_have_platform_egl
+  gtk_wayland_dep = dependency('gtk4-wayland', required: false)
+  if gtk_wayland_dep.found()
+    gtk_deps += [gtk_wayland_dep, gstglwayland_dep]
+    have_gtk_gl_windowing = true
+  endif
+endif
+
+if gst_gl_have_platform_egl
+  gtk_deps += gstglegl_dep
+endif
+
 subdir('gst')
 configure_file(output: 'config.h', configuration: cdata)