How to use SetTraceLogCallback()?

[Charadon]

I'm trying to use SetTraceLogCallback, but I run into a few issues:

1. I get a format exception because java doesn't have the %i formatter.
2. I have no idea how to get the va_list from the TraceLogCallback struct (Pointer args).

I can easily get the string from the BytePointer text variable, and I can also easily just replace the %i with %d, but actually figuring out how to use the Pointer args variable is really confusing me.

Example code:

private static class LogCallback extends TraceLogCallback {
    @Override
    public void call(int logLevel, BytePointer text, Pointer args) {
        
    }
}

[mohammadrezwankhan]

TraceLogCallback is exposing raylib’s native printf machinery, not a pre-formatted Java string.

Raylib declares the callback as void (*)(int logLevel, const char *text, va_list args) (header). In TraceLog, text is passed unchanged as the format string and the native va_list is passed separately. Jaylib therefore generates the third parameter as @ByVal @Cast("va_list*") Pointer (generated Javadoc).

That explains both symptoms:

• %i is valid for C printf, but Java’s Formatter uses %d; more importantly, text is only the template, so replacing %i cannot recover the missing arguments.
• Pointer args is an opaque, ABI-specific va_list. It has no type metadata, so reading it with getInt(), getLong(), etc. is not portable or safe; the format string is what tells native code how to consume it.

If you only need the template, this is all you can do in the Java callback:

@Override
public void call(int level, BytePointer text, Pointer args) {
    System.err.println(text.getString()); // e.g. "value=%i"
}

For the actual expanded message, add a tiny native bridge and bind a second callback whose second argument is const char *:

static FormattedTraceLogCallback javaLog;

static void bridge_trace_log(int level, const char *fmt, va_list ap)
{
    char buf[4096];
    va_list copy;
    va_copy(copy, ap);
    vsnprintf(buf, sizeof buf, fmt, copy);
    va_end(copy);
    if (javaLog) javaLog(level, buf);
}

void SetFormattedTraceLogCallback(FormattedTraceLogCallback cb)
{
    javaLog = cb;
    SetTraceLogCallback(cb ? bridge_trace_log : NULL);
}

Expose FormattedTraceLogCallback as (int, const char*) in the Jaylib preset (or a small companion JNI/JavaCPP header), then the Java callback receives a normal BytePointer containing INFO: value=42; no String.format and no va_list decoding are needed. Keep the bridge native because va_list layouts differ across platforms and raylib owns the original argument list. If you cannot add native code, there is no portable Java-only way to reconstruct the formatted values from Pointer args.

[Charadon]

I figured it would probably require native code, just wanted to make sure I wasn't missing anything obvious lol. Thanks for the quick answer!