And implemented the bare bones of uiControlOSVtable on GTK+.

test/meson.build

@@ -23,6 +23,7 @@ elif libui_OS == 'darwin'
 else
 	libui_test_sources += [
 		'controls_unix.c',
+		'controls_unix_errors.cpp',
 	]
 endif
 

test/test_unix.h

@@ -0,0 +1,3 @@
+// 10 june 2019
+#define libuiOSHeader "../ui_unix.h"
+#include "test.h"

ui_unix.h

@@ -11,6 +11,10 @@ This file assumes that you have included <gtk/gtk.h> and "ui.h" beforehand. It p
 extern "C" {
 #endif
 
+struct uiControlOSVtable {
+	size_t Size;
+};
+
 #ifdef __cplusplus
 }
 #endif

unix/controls.c

@@ -0,0 +1,20 @@
+// 8 june 2019
+#include "uipriv_unix.h"
+
+bool uiprivOSVtableValid(const uiControlOSVtable *osVtable, const char *func)
+{
+	if (osVtable->Size != sizeof (uiControlOSVtable)) {
+		uiprivProgrammerErrorWrongStructSize(osVtable->Size, "uiControlOSVtable", func);
+		return false;
+	}
+	return true;
+}
+
+uiControlOSVtable *uiprivCloneOSVtable(const uiControlOSVtable *osVtable)
+{
+	uiControlOSVtable *v2;
+
+	v2 = uiprivNew(uiControlOSVtable);
+	*v2 = *osVtable;
+	return v2;
+}

unix/meson.build

@@ -1,6 +1,7 @@
 # 23 march 2019
 
 libui_sources += [
+	'unix/controls.c',
 	'unix/main.c',
 ]