Allow passing user data to callback

It is often useful or necessary to pass custom data to a callback.
Add an argument to the callback registering function to pass a void
pointer object to the callback each time it is called.

1 files changed, 9 insertions, 3 deletions

diff --git a/libass/ass_library.c b/libass/ass_library.c
index 2a8f5b2..9b6da02 100644
--- a/libass/ass_library.c
+++ b/libass/ass_library.c
@@ -28,7 +28,7 @@
 #include "ass_library.h"
 #include "ass_utils.h"
 
-static void ass_msg_handler(int level, char *fmt, va_list *va)
+static void ass_msg_handler(int level, char *fmt, va_list *va, void *data)
 {
     if (level > MSGL_INFO)
         return;
@@ -132,11 +132,17 @@ void ass_clear_fonts(ass_library_t *priv)
  * Register a message callback function with libass.  Without setting one,
  * a default handler is used which prints everything with MSGL_INFO or
  * higher to the standard output.
+ *
+ * \param msg_cb the callback function
+ * \param data additional data that will be passed to the callback
  */
 void ass_set_message_cb(ass_library_t *priv,
-                        void (*msg_cb)(int, char *, va_list *))
+                        void (*msg_cb)(int, char *, va_list *, void *),
+                        void *data)
 {
-    if (msg_cb)
+    if (msg_cb) {
         priv->msg_callback = msg_cb;
+        priv->msg_callback_data = data;
+    }
 }