meta: Move the clear operation to its own vfunc

Some transforms always assumed that the transformation was some kind
of copy. So adding a "clear" operation didn't work out in practice.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/5830>

girs/Gst-1.0.gir

@@ -22164,16 +22164,6 @@ In hindsight, this tag should have been called "memory-layout".</doc>
       <source-position filename="../subprojects/gstreamer/gst/gstmeta.h"/>
       <type name="utf8" c:type="gchar*"/>
     </constant>
-    <function-macro name="META_TRANSFORM_IS_CLEAR" c:identifier="GST_META_TRANSFORM_IS_CLEAR" version="1.24" introspectable="0">
-      <doc xml:space="preserve" filename="../subprojects/gstreamer/gst/gstmeta.h">Check if the transform type is clearing the content of the meta without
-freeing it.</doc>
-      <source-position filename="../subprojects/gstreamer/gst/gstmeta.h"/>
-      <parameters>
-        <parameter name="type">
-          <doc xml:space="preserve" filename="../subprojects/gstreamer/gst/gstmeta.h">a transform type</doc>
-        </parameter>
-      </parameters>
-    </function-macro>
     <function-macro name="META_TRANSFORM_IS_COPY" c:identifier="GST_META_TRANSFORM_IS_COPY" introspectable="0">
       <doc xml:space="preserve" filename="../subprojects/gstreamer/gst/gstmeta.h">Check if the transform type is a copy transform</doc>
       <source-position filename="../subprojects/gstreamer/gst/gstmeta.h"/>
@@ -26093,6 +26083,24 @@ transform function.</doc>
         </parameters>
       </function>
     </record>
+    <callback name="MetaClearFunction" c:type="GstMetaClearFunction" version="1.24">
+      <doc xml:space="preserve" filename="../subprojects/gstreamer/gst/gstmeta.h">Clears the content of the meta. This will be called by the GstBufferPool
+when a pooled buffer is returned.</doc>
+      <source-position filename="../subprojects/gstreamer/gst/gstmeta.h"/>
+      <return-value transfer-ownership="none">
+        <type name="none" c:type="void"/>
+      </return-value>
+      <parameters>
+        <parameter name="buffer" transfer-ownership="none">
+          <doc xml:space="preserve" filename="../subprojects/gstreamer/gst/gstmeta.h">a #GstBuffer</doc>
+          <type name="Buffer" c:type="GstBuffer*"/>
+        </parameter>
+        <parameter name="meta" transfer-ownership="none">
+          <doc xml:space="preserve" filename="../subprojects/gstreamer/gst/gstmeta.h">a #GstMeta</doc>
+          <type name="Meta" c:type="GstMeta*"/>
+        </parameter>
+      </parameters>
+    </callback>
     <callback name="MetaDeserializeFunction" c:type="GstMetaDeserializeFunction" version="1.24">
       <doc xml:space="preserve" filename="../subprojects/gstreamer/gst/gstmeta.h">Recreate a #GstMeta from serialized data returned by
 #GstMetaSerializeFunction and add it to @buffer.</doc>
@@ -26196,6 +26204,12 @@ meta.</doc>
 meta.</doc>
         <type name="MetaDeserializeFunction" c:type="GstMetaDeserializeFunction"/>
       </field>
+      <field name="clear_func" version="1.24" writable="1">
+        <doc xml:space="preserve" filename="../subprojects/gstreamer/gst/gstmeta.h">Function for clearing the metadata, or %NULL if not supported by this
+meta. This is called by the buffer pool when a buffer is returned for
+pooled metas.</doc>
+        <type name="MetaClearFunction" c:type="GstMetaClearFunction"/>
+      </field>
       <method name="is_custom" c:identifier="gst_meta_info_is_custom" version="1.20">
         <source-position filename="../subprojects/gstreamer/gst/gstmeta.h"/>
         <return-value transfer-ownership="none">

subprojects/gst-plugins-bad/gst-libs/gst/analytics/gstanalyticsmeta.c

@@ -344,39 +344,41 @@ gst_analytics_relation_meta_transform (GstBuffer * transbuf,
 
       return FALSE;
     }
-  } else if (GST_META_TRANSFORM_IS_CLEAR (type)) {
-    GstAnalyticsRelationMeta *rmeta = (GstAnalyticsRelationMeta *) meta;
-    gsize adj_mat_data_size =
-        (sizeof (guint8) * rmeta->rel_order * rmeta->rel_order);
-
-    rmeta->next_id = 0;
-    rmeta->offset = 0;
-    rmeta->length = 0;
-    if (adj_mat_data_size) {
-      /* Only clear data and not lines addresses occupying begining of this
-       * array. */
-      memset (rmeta->adj_mat + rmeta->rel_order, 0, adj_mat_data_size);
-    }
-
-    return TRUE;
   }
 
   return FALSE;
 }
 
+static void
+gst_analytics_relation_meta_clear (GstBuffer * buffer, GstMeta * meta)
+{
+  GstAnalyticsRelationMeta *rmeta = (GstAnalyticsRelationMeta *) meta;
+  gsize adj_mat_data_size =
+      (sizeof (guint8) * rmeta->rel_order * rmeta->rel_order);
+
+  rmeta->next_id = 0;
+  rmeta->offset = 0;
+  rmeta->length = 0;
+  if (adj_mat_data_size) {
+    /* Only clear data and not lines addresses occupying begining of this
+     * array. */
+    memset (rmeta->adj_mat + rmeta->rel_order, 0, adj_mat_data_size);
+  }
+}
 
 const GstMetaInfo *
 gst_analytics_relation_meta_get_info (void)
 {
   static const GstMetaInfo *info = NULL;
   if (g_once_init_enter ((GstMetaInfo **) & info)) {
-    const GstMetaInfo *meta =
+    GstMetaInfo *meta = (GstMetaInfo *)
         gst_meta_register (GST_ANALYTICS_RELATION_META_API_TYPE,
         "GstAnalyticsRelationMeta",
         sizeof (GstAnalyticsRelationMeta),
         gst_analytics_relation_meta_init,
         gst_analytics_relation_meta_free,
         gst_analytics_relation_meta_transform);
+    meta->clear_func = gst_analytics_relation_meta_clear;
     g_once_init_leave ((GstMetaInfo **) & info, (GstMetaInfo *) meta);
   }
   return info;

subprojects/gstreamer/gst/gstbufferpool.c

@@ -1221,10 +1221,8 @@ remove_meta_unpooled (GstBuffer * buffer, GstMeta ** meta, gpointer user_data)
     const GstMetaInfo *info = (*meta)->info;
 
     /* If we can clear it, don't free it */
-    if (info->transform_func) {
+    if (info->clear_func)
-      info->transform_func (NULL, *meta, buffer, _gst_meta_transform_clear,
+      info->clear_func (buffer, *meta);
-          NULL);
-    }
   }
   return TRUE;
 }

subprojects/gstreamer/gst/gstmeta.c

@@ -56,7 +56,6 @@ static GHashTable *metainfo = NULL;
 static GRWLock lock;
 
 GQuark _gst_meta_transform_copy;
-GQuark _gst_meta_transform_clear;
 GQuark _gst_meta_tag_memory;
 GQuark _gst_meta_tag_memory_reference;
 
@@ -82,7 +81,6 @@ _priv_gst_meta_initialize (void)
   metainfo = g_hash_table_new_full (g_str_hash, g_str_equal, NULL, free_info);
 
   _gst_meta_transform_copy = g_quark_from_static_string ("gst-copy");
-  _gst_meta_transform_clear = g_quark_from_static_string ("gst-clear");
   _gst_meta_tag_memory = g_quark_from_static_string ("memory");
   _gst_meta_tag_memory_reference =
       g_quark_from_static_string ("memory-reference");
@@ -430,7 +428,7 @@ gst_meta_register_internal (GType api, const gchar * impl, gsize size,
   if (type == G_TYPE_INVALID)
     return NULL;
 
-  info = (GstMetaInfo *) g_new (GstMetaInfoImpl, 1);
+  info = (GstMetaInfo *) g_new0 (GstMetaInfoImpl, 1);
   info->api = api;
   info->type = type;
   info->size = size;

subprojects/gstreamer/gst/gstmeta.h

@@ -197,27 +197,6 @@ typedef struct {
   gsize size;
 } GstMetaTransformCopy;
 
-/**
- * gst_meta_transform_clear:
- *
- * GQuark for the "gst-clear" transform.
- *
- * Since: 1.24
- */
-
-GST_API GQuark _gst_meta_transform_clear;
-
-/**
- * GST_META_TRANSFORM_IS_CLEAR:
- * @type: a transform type
- *
- * Check if the transform type is clearing the content of the meta without
- * freeing it.
- *
- * Since: 1.24
- */
-#define GST_META_TRANSFORM_IS_CLEAR(type) ((type) == _gst_meta_transform_clear)
-
 /**
  * GstMetaTransformFunction:
  * @transbuf: a #GstBuffer
@@ -301,6 +280,18 @@ typedef gboolean (*GstMetaSerializeFunction) (const GstMeta *meta,
 typedef GstMeta *(*GstMetaDeserializeFunction) (const GstMetaInfo *info,
     GstBuffer *buffer, const guint8 *data, gsize size, guint8 version);
 
+/**
+ * GstMetaClearFunction:
+ * @buffer: a #GstBuffer
+ * @meta: a #GstMeta
+ *
+ * Clears the content of the meta. This will be called by the GstBufferPool
+ * when a pooled buffer is returned.
+ *
+ * Since: 1.24
+ */
+typedef void (*GstMetaClearFunction) (GstBuffer *buffer, GstMeta *meta);
+
 /**
  * GstMetaInfo.serialize_func:
  *
@@ -319,6 +310,16 @@ typedef GstMeta *(*GstMetaDeserializeFunction) (const GstMetaInfo *info,
  * Since: 1.24
  */
 
+/**
+ * GstMetaInfo.clear_func:
+ *
+ * Function for clearing the metadata, or %NULL if not supported by this
+ * meta. This is called by the buffer pool when a buffer is returned for
+ * pooled metas.
+ *
+ * Since: 1.24
+ */
+
 /**
  * GstMetaInfo:
  * @api: tag identifying the metadata structure and api
@@ -345,6 +346,7 @@ struct _GstMetaInfo {
   GstMetaTransformFunction   transform_func;
   GstMetaSerializeFunction   serialize_func;
   GstMetaDeserializeFunction deserialize_func;
+  GstMetaClearFunction       clear_func;
 
   /* No padding needed, GstMetaInfo is always allocated by GStreamer and is
    * not subclassable or stack-allocatable, so we can extend it as we please