lua: add support to use ipairs() with some collections (sprites/tags/slices/layers/frames/cels)

src/app/script/cels_class.cpp

@@ -50,9 +50,10 @@ int Cels_index(lua_State* L)
 {
   auto obj = get_obj<CelsObj>(L, 1);
   const int i = lua_tointeger(L, 2);
-  if (i < 1 || i > obj->cels.size())
-    return luaL_error(L, "index out of bounds %d", i);
-  push_ptr<Cel>(L, obj->cels[i-1]);
+  if (i >= 1 && i <= obj->cels.size())
+    push_ptr<Cel>(L, obj->cels[i-1]);
+  else
+    lua_pushnil(L);
   return 1;
 }
 

src/app/script/frames_class.cpp

@@ -45,9 +45,10 @@ int Frames_index(lua_State* L)
 {
   auto obj = get_obj<FramesObj>(L, 1);
   const int i = lua_tonumber(L, 2);
-  if (i < 1 || i > obj->sprite->totalFrames())
-    return luaL_error(L, "index out of bounds %d", i);
-  push_sprite_frame(L, obj->sprite, i-1);
+  if (i >= 1 && i <= obj->sprite->totalFrames())
+    push_sprite_frame(L, obj->sprite, i-1);
+  else
+    lua_pushnil(L);
   return 1;
 }
 

src/app/script/layers_class.cpp

@@ -48,9 +48,10 @@ int Layers_index(lua_State* L)
 {
   auto obj = get_obj<LayersObj>(L, 1);
   const int i = lua_tonumber(L, 2);
-  if (i < 1 || i > int(obj->layers.size()))
-    return luaL_error(L, "index out of bounds %d", i);
-  push_ptr<Layer>(L, obj->layers[i-1]);
+  if (i >= 1 && i <= int(obj->layers.size()))
+    push_ptr<Layer>(L, obj->layers[i-1]);
+  else
+    lua_pushnil(L);
   return 1;
 }
 

src/app/script/slices_class.cpp

@@ -44,9 +44,10 @@ int Slices_index(lua_State* L)
   auto obj = get_obj<SlicesObj>(L, 1);
   auto& slices = obj->sprite->slices();
   const int i = lua_tonumber(L, 2);
-  if (i < 1 || i > int(slices.size()))
-    return luaL_error(L, "index out of bounds %d", i);
-  push_ptr<Slice>(L, *(slices.begin()+i-1));
+  if (i >= 1 && i <= int(slices.size()))
+    push_ptr<Slice>(L, *(slices.begin()+i-1));
+  else
+    lua_pushnil(L);
   return 1;
 }
 

src/app/script/sprites_class.cpp

@@ -52,9 +52,10 @@ int Sprites_index(lua_State* L)
 {
   auto obj = get_obj<SpritesObj>(L, 1);
   const int i = lua_tonumber(L, 2);
-  if (i < 1 || i > int(obj->docs.size()))
-    return luaL_error(L, "index out of bounds %d", i);
-  push_ptr<Sprite>(L, obj->docs[i-1]->sprite());
+  if (i >= 1 && i <= int(obj->docs.size()))
+    push_ptr<Sprite>(L, obj->docs[i-1]->sprite());
+  else
+    lua_pushnil(L);
   return 1;
 }
 

src/app/script/tags_class.cpp

@@ -46,9 +46,10 @@ int Tags_index(lua_State* L)
   auto obj = get_obj<TagsObj>(L, 1);
   auto& tags = obj->sprite->frameTags();
   const int i = lua_tonumber(L, 2);
-  if (i < 1 || i > int(tags.size()))
-    return luaL_error(L, "index out of bounds %d", i);
-  push_ptr<FrameTag>(L, *(tags.begin()+i-1));
+  if (i >= 1 && i <= int(tags.size()))
+    push_ptr<FrameTag>(L, *(tags.begin()+i-1));
+  else
+    lua_pushnil(L);
   return 1;
 }