add log interface (lv_log) but still there are no log messages added

lv_misc/lv_log.c

@@ -0,0 +1,80 @@
+/**
+ * @file lv_log.c
+ *
+ */
+
+/*********************
+ *      INCLUDES
+ *********************/
+#include "lv_log.h"
+#if USE_LV_LOG
+
+#if LV_LOG_PRINTF
+#include <string.h>
+#endif
+/*********************
+ *      DEFINES
+ *********************/
+
+/**********************
+ *      TYPEDEFS
+ **********************/
+
+/**********************
+ *  STATIC PROTOTYPES
+ **********************/
+
+/**********************
+ *  STATIC VARIABLES
+ **********************/
+static void (*print_cb)(lv_log_level_t , const char *, uint32_t ,  const char *);
+
+/**********************
+ *      MACROS
+ **********************/
+
+/**********************
+ *   GLOBAL FUNCTIONS
+ **********************/
+
+/**
+ * Register custom print (or anything else) function to call when log is added
+ * @param f a function pointer:
+ *          `void my_print (lv_log_level_t level, const char * file, uint32_t line, const char * dsc)`
+ */
+void lv_log_register_print(void f(lv_log_level_t , const char *, uint32_t ,  const char *))
+{
+	print_cb = f;
+}
+
+/**
+ * Add a log
+ * @param level the level of log. (From `lv_log_level_t` enum)
+ * @param file name of the file when the log added
+ * @param line line number in the source code where the log added
+ * @param dsc description of the log
+ */
+void lv_log_add(lv_log_level_t level, const char * file, uint32_t line, const char * dsc)
+{
+	if(level >= _LV_LOG_LEVEL_NUM) return;		/*Invalid level*/
+
+	if((level == LV_LOG_LEVEL_INFO && LV_LOG_INFO)  ||
+	   (level == LV_LOG_LEVEL_WARN && LV_LOG_WARN)  ||
+	   (level == LV_LOG_LEVEL_ERROR && LV_LOG_ERROR) ||
+	   (level == LV_LOG_LEVEL_USER && LV_LOG_USER))
+	{
+
+#if LV_LOG_PRINTF
+		static const char * lvl_prefix[] = {"Info", "Warn", "Error", "User"};
+		printf("%s %s:%d:   %s\n", lvl_prefix[level], file, line, dsc);
+#else
+		if(print_cb) print_cb(level, file, line, dsc);
+#endif
+	}
+}
+
+/**********************
+ *   STATIC FUNCTIONS
+ **********************/
+
+#endif /*USE_LV_LOG*/