Hooks: central vtable install with restore support

Move vtable patching into hooks.cpp: one call clones the table, validates every
slot, records the originals and installs the clone. Installs happen from the
setup, game and paint threads, so the bookkeeping is mutex-protected.

Client, CInput, IVModelRender, IStudioRender and ISurface all use it, and
hooks_restore_all() can now put every interface back (previously impossible).

1 files changed, 28 insertions, 0 deletions

diff --git a/src/hooks.h b/src/hooks.h
new file mode 100644
index 0000000..084698f
--- /dev/null
+++ b/src/hooks.h
@@ -0,0 +1,28 @@
+#ifndef HL2H_HOOKS_H
+#define HL2H_HOOKS_H
+
+#include <cstddef>
+
+// One patched vtable slot. `original` receives the untouched function pointer
+// (it may be null if the caller does not need it).
+struct VtablePatch {
+  int slot;
+  void *replacement;
+  void **original;
+};
+
+// Clone `iface`'s vtable (preserving the Itanium ABI header), apply all
+// patches, and install the clone on the object. All slots belong to the same
+// interface. Returns false and leaves the object untouched if cloning fails or
+// any slot is out of range.
+bool hooks_install_vtable(void *iface, size_t slots, const VtablePatch *patches,
+                          int count);
+
+// Restore every patched interface's original vtable in reverse install order.
+// Intended for tests and shutdown; the cheat normally lives as long as the
+// process does.
+void hooks_restore_all();
+
+int hooks_installed_count();
+
+#endif