Fix Lua 0-indexing

Include/RmlUi/Lua/Utilities.h

@@ -46,6 +46,14 @@ void RMLUILUA_API PushVariant(lua_State* L, const Variant* var);
 /** Populate the variant based on the Lua value at the given index */
 void RMLUILUA_API GetVariant(lua_State* L, int index, Variant* variant);
 
+// Converts index from 0-based to 1-based before pushing it to the stack
+void RMLUILUA_API PushIndex(lua_State* L, int index);
+
+// Returns 0-based index after retrieving from stack and converting from 1-based
+// The index parameter refers to the position on the stack and is not affected
+// by the conversion
+int RMLUILUA_API GetIndex(lua_State* L, int index);
+
 //Helper function, so that the types don't have to define individual functions themselves
 // to fill the Elements.As table
 template<typename ToType>

Source/Lua/Element.cpp

@@ -182,7 +182,7 @@ int ElementGetElementsByTagName(lua_State* L, Element* obj)
     lua_newtable(L);
     for(unsigned int i = 0; i < list.size(); i++)
     {
-        lua_pushinteger(L,i);
+        PushIndex(L,i);
         LuaType<Element>::push(L,list[i],false);
         lua_settable(L,-3); //-3 is the table
     }

Source/Lua/Elements/ElementFormControlSelect.cpp

@@ -45,7 +45,7 @@ int ElementFormControlSelectAdd(lua_State* L, ElementFormControlSelect* obj)
     const char* value = luaL_checkstring(L,2);
     int before = -1; //default
     if(lua_gettop(L) >= 3)
-        before = (int)luaL_checkinteger(L,3);
+        before = GetIndex(L,3);
 
     int index = obj->Add(rml,value,before);
     lua_pushinteger(L,index);
@@ -54,7 +54,7 @@ int ElementFormControlSelectAdd(lua_State* L, ElementFormControlSelect* obj)
 
 int ElementFormControlSelectRemove(lua_State* L, ElementFormControlSelect* obj)
 {
-    int index = (int)luaL_checkinteger(L,1);
+    int index = GetIndex(L,1);
     obj->Remove(index);
     return 0;
 }
@@ -81,7 +81,7 @@ int ElementFormControlSelectGetAttrselection(lua_State* L)
     ElementFormControlSelect* obj = LuaType<ElementFormControlSelect>::check(L,1);
     RMLUI_CHECK_OBJ(obj);
     int selection = obj->GetSelection();
-    lua_pushinteger(L,selection);
+    PushIndex(L,selection);
     return 1;
 }
 
@@ -91,7 +91,7 @@ int ElementFormControlSelectSetAttrselection(lua_State* L)
 {
     ElementFormControlSelect* obj = LuaType<ElementFormControlSelect>::check(L,1);
     RMLUI_CHECK_OBJ(obj);
-    int selection = (int)luaL_checkinteger(L,2);
+    int selection = GetIndex(L,2);
     obj->SetSelection(selection);
     return 0;
 }

Source/Lua/Elements/ElementTabSet.cpp

@@ -38,7 +38,7 @@ namespace Lua {
 int ElementTabSetSetPanel(lua_State* L, ElementTabSet* obj)
 {
     RMLUI_CHECK_OBJ(obj);
-    int index = (int)luaL_checkinteger(L,1);
+    int index = GetIndex(L,1);
     const char* rml = luaL_checkstring(L,2);
 
     obj->SetPanel(index,rml);
@@ -48,7 +48,7 @@ int ElementTabSetSetPanel(lua_State* L, ElementTabSet* obj)
 int ElementTabSetSetTab(lua_State* L, ElementTabSet* obj)
 {
     RMLUI_CHECK_OBJ(obj);
-    int index = (int)luaL_checkinteger(L,1);
+    int index = GetIndex(L,1);
     const char* rml = luaL_checkstring(L,2);
 
     obj->SetTab(index,rml);
@@ -62,7 +62,7 @@ int ElementTabSetGetAttractive_tab(lua_State* L)
     ElementTabSet* obj = LuaType<ElementTabSet>::check(L,1);
     RMLUI_CHECK_OBJ(obj);
     int tab = obj->GetActiveTab();
-    lua_pushinteger(L,tab);
+    PushIndex(L,tab);
     return 1;
 }
 
@@ -81,7 +81,7 @@ int ElementTabSetSetAttractive_tab(lua_State* L)
 {
     ElementTabSet* obj = LuaType<ElementTabSet>::check(L,1);
     RMLUI_CHECK_OBJ(obj);
-    int tab = (int)luaL_checkinteger(L,2);
+    int tab = GetIndex(L,2);
     obj->SetActiveTab(tab);
     return 0;
 }

Source/Lua/EventParametersProxy.cpp

@@ -31,6 +31,7 @@
 #include <RmlUi/Core/Variant.h>
 #include <RmlUi/Core/Dictionary.h>
 #include "Pairs.h"
+#include <cstring>
 
 
 namespace Rml {
@@ -55,7 +56,15 @@ int EventParametersProxy__index(lua_State* L)
         const char* key = lua_tostring(L,2);
 		auto it = obj->owner->GetParameters().find(key);
 		const Variant* param = (it == obj->owner->GetParameters().end() ? nullptr : &it->second);
-        PushVariant(L,param);
+        if (obj->owner->GetId() == EventId::Tabchange &&
+            std::strcmp(key, "tab_index") == 0 &&
+            param &&
+            param->GetType() == Variant::Type::INT)
+        {
+            PushIndex(L,param->Get<int>());
+        }
+        else
+            PushVariant(L,param);
         return 1;
     }
     else

Source/Lua/Utilities.cpp

@@ -113,5 +113,16 @@ void GetVariant(lua_State* L, int index, Variant* variant)
 		break;
 	}
 }
+
+void PushIndex(lua_State* L, int index)
+{
+	lua_pushinteger(L, index + 1);
+}
+
+int GetIndex(lua_State* L, int index)
+{
+	return (int)luaL_checkinteger(L, index) - 1;
+}
+
 } // namespace Lua
 } // namespace Rml