libobs: Use windows wide <-> UTF8 conversion

If on windows, use the windows UTF conversion functions due to the fact
that the existing utf code is meant for 32bit wide characters, while the
windows conversion functions will properly handle 16bit wide characters.

libobs/util/utf8.c

@@ -17,6 +17,58 @@
 
 #include "utf8.h"
 
+#ifdef _WIN32
+
+#include <windows.h>
+#include "c99defs.h"
+
+static inline bool has_utf8_bom(const char *in_char)
+{
+	uint8_t *in = (uint8_t*)in_char;
+	return (in && in[0] == 0xef && in[1] == 0xbb && in[2] == 0xbf);
+}
+
+size_t utf8_to_wchar(const char *in, size_t insize, wchar_t *out,
+		size_t outsize, int flags)
+{
+	int i_insize = (int)insize;
+	int ret;
+
+	if (i_insize == 0)
+		i_insize = strlen(in);
+
+	/* prevent bom from being used in the string */
+	if (has_utf8_bom(in)) {
+		if (i_insize >= 3) {
+			in += 3;
+			insize -= 3;
+		}
+	}
+
+	ret = MultiByteToWideChar(CP_UTF8, 0, in, i_insize, out, (int)outsize);
+
+	UNUSED_PARAMETER(flags);
+	return (ret > 0) ? (size_t)ret : 0;
+}
+
+size_t wchar_to_utf8(const wchar_t *in, size_t insize, char *out,
+		size_t outsize, int flags)
+{
+	int i_insize = (int)insize;
+	int ret;
+
+	if (i_insize == 0)
+		i_insize = wcslen(in);
+
+	ret = WideCharToMultiByte(CP_UTF8, 0, in, i_insize, out, (int)outsize,
+			NULL, NULL);
+
+	UNUSED_PARAMETER(flags);
+	return (ret > 0) ? (size_t)ret : 0;
+}
+
+#else
+
 #define _NXT	0x80
 #define _SEQ2	0xc0
 #define _SEQ3	0xe0
@@ -318,3 +370,5 @@ size_t wchar_to_utf8(const wchar_t *in, size_t insize, char *out,
 
 	return total;
 }
+
+#endif