Tweak the interpose API, and fix a couple of bugs.

library/VTableInterpose.cpp

@@ -161,6 +161,7 @@ VMethodInterposeLinkBase::VMethodInterposeLinkBase(virtual_identity *host, int v
     : host(host), vmethod_idx(vmethod_idx), interpose_method(interpose_method), chain_mptr(chain_mptr),
       saved_chain(NULL), next(NULL), prev(NULL)
 {
+    assert(vmethod_idx >= 0 && interpose_method != NULL);
 }
 
 VMethodInterposeLinkBase::~VMethodInterposeLinkBase()
@@ -198,6 +199,7 @@ bool VMethodInterposeLinkBase::apply()
         return false;
 
     set_chain(old_ptr);
+    host->interpose_list.push_back(this);
 
     // Link into the chain if any
     if (old_link)

library/include/VTableInterpose.h

@@ -81,12 +81,18 @@ namespace DFHack
         return addr_to_method_pointer<P>(identity.get_vmethod_ptr(idx));
     }
 
-    /* VMethod interpose API
+    /* VMethod interpose API.
+
+       This API allows replacing an entry in the original vtable
+       with code defined by DFHack, while retaining ability to
+       call the original code. The API can be safely used from
+       plugins, and multiple hooks for the same vmethod are
+       automatically chained in undefined order.
 
        Usage:
 
-       struct my_hack : public someclass {
+       struct my_hack : df::someclass {
-           typedef someclass interpose_base;
+           typedef df::someclass interpose_base;
 
            DEFINE_VMETHOD_INTERPOSE(void, foo, (int arg)) {
                ...
@@ -98,7 +104,12 @@ namespace DFHack
        IMPLEMENT_VMETHOD_INTERPOSE(my_hack, foo);
 
        void init() {
-           my_hack::interpose_foo.apply()
+           if (!INTERPOSE_HOOK(my_hack, foo).apply())
+               error();
+       }
+
+       void shutdown() {
+           INTERPOSE_HOOK(my_hack, foo).remove();
        }
      */
 
@@ -112,6 +123,7 @@ namespace DFHack
         class::interpose_##name(&class::interpose_base::name, &class::interpose_fn_##name);
 
 #define INTERPOSE_NEXT(name) (this->*interpose_##name.chain)
+#define INTERPOSE_HOOK(class, name) (class::interpose_##name)
 
     class DFHACK_EXPORT VMethodInterposeLinkBase {
         /*

plugins/devel/vshook.cpp

@@ -33,9 +33,12 @@ struct title_hook : df::viewscreen_titlest {
             uint8_t *buf = gps->screen;
             int32_t *stp = gps->screentexpos;
 
-            for (const char *p = "DFHack " DFHACK_VERSION; *p; p++) {
+            for (const char *p = "DFHack " DFHACK_VERSION;
-                *buf++ = *p; *buf++ = 7; *buf++ = 0; *buf++ = 1;
+                 *p && buf < gps->screen_limit;
-                *stp++ = 0;
+                 p++, buf += gps->dimy*4, stp += gps->dimy)
+            {
+                buf[0] = *p; buf[1] = 7; buf[2] = 0; buf[3] = 1;
+                *stp = 0;
             }
         }
     }
@@ -47,7 +50,7 @@ DFhackCExport command_result plugin_init ( color_ostream &out, std::vector <Plug
 {
     if (gps)
     {
-        if (!title_hook::interpose_render.apply())
+        if (!INTERPOSE_HOOK(title_hook, render).apply())
             out.printerr("Could not interpose viewscreen_titlest::render\n");
     }
 
@@ -56,6 +59,6 @@ DFhackCExport command_result plugin_init ( color_ostream &out, std::vector <Plug
 
 DFhackCExport command_result plugin_shutdown ( color_ostream &out )
 {
-    title_hook::interpose_render.remove();
+    INTERPOSE_HOOK(title_hook, render).remove();
     return CR_OK;
 }