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, 59 insertions, 0 deletions

diff --git a/src/hooks.cpp b/src/hooks.cpp
new file mode 100644
index 0000000..215ecfd
--- /dev/null
+++ b/src/hooks.cpp
@@ -0,0 +1,59 @@
+// hooks.cpp — vtable hook installation and teardown bookkeeping.
+#include "hl2h.h"
+
+#include <mutex>
+#include <vector>
+
+namespace {
+
+struct Installed {
+  void *iface;
+  void **old_vt;
+};
+
+std::mutex g_hook_mu;
+std::vector<Installed> g_installed;
+
+} // namespace
+
+bool hooks_install_vtable(void *iface, size_t slots, const VtablePatch *patches,
+                          int count) {
+  if (!iface || !patches || count <= 0)
+    return false;
+  void **old = *(void ***)iface;
+  if (!old)
+    return false;
+  for (int i = 0; i < count; i++) {
+    if (patches[i].slot < 0 || (size_t)patches[i].slot >= slots) {
+      logf("hooks: slot %d out of range (table has %u)", patches[i].slot,
+           (unsigned)slots);
+      return false;
+    }
+  }
+
+  void **clone = vtable_clone(iface, slots);
+  if (!clone)
+    return false;
+  for (int i = 0; i < count; i++) {
+    if (patches[i].original)
+      *patches[i].original = old[patches[i].slot];
+    clone[patches[i].slot] = patches[i].replacement;
+  }
+
+  std::lock_guard<std::mutex> lock(g_hook_mu);
+  *(void ***)iface = clone;
+  g_installed.push_back({iface, old});
+  return true;
+}
+
+void hooks_restore_all() {
+  std::lock_guard<std::mutex> lock(g_hook_mu);
+  for (auto it = g_installed.rbegin(); it != g_installed.rend(); ++it)
+    *(void ***)it->iface = it->old_vt;
+  g_installed.clear();
+}
+
+int hooks_installed_count() {
+  std::lock_guard<std::mutex> lock(g_hook_mu);
+  return (int)g_installed.size();
+}