Useful Code Snippets in Paracraft

Paracraft Filters

Filters is the recommended way for plugin/app developers to extend or modify paracraft.

Mod interface also use filters to implement all plugin interface, therefore Mod Manager is an example of how to add filters to various integration points in paracraft. To extend paracraft, one can either use filters or overwrite virtual functions on mod interface. It is therefore possible for an application to add high priority filters to disable/modify data after all mod interface filters.

It is good practice to install filters only once at the very beginning. A good place to install filters is before Game.Start is called or in the mod:init function. One can also dynamically add/remove filters at runtime, just be sure to add your filters before they are applied.

What Is the Filter To Use For World Login

It is not trivial to define a filter (event) when a world is fully loaded, because everything is asynchronously loaded. The following filters are applied at various stage of world loading:

  • “ActivateDesktop”, bIgnoreDefaultDesktop, mode: called when desktop mode is changed. This is the place to initialize your custom GUI.
  • “handleLogin”, packet_login: whenever client received confirmed login packet from server. (only called in remote world)
  • “PlayerHasLoginPosition”, nil, x,y,z: called whenever the player is at its spawn position in both local or remote world.This filter is most close to when a world is fully loaded.
One may start a one-time timer in any of these events to check if the world is fully loaded. If so, stop the timer and do whatever you want.

Register a New Block

Please see Test Sample in ParacraftSDK’s _mod folder.

-- register a new block item, id < 512 is internal blocks, which is not recommended to modify. 
GameLogic.GetFilters():add_filter("block_types", function(xmlRoot) 
    local blocks = commonlib.XPath.selectNode(xmlRoot, "/blocks/");
    if(blocks) then
        blocks[#blocks+1] = {name="block", attr={
            id = 512, threeSideTex = "true",
            text = "Demo Item", name = "DemoItem",
            obstruction="true", solid="true", cubeMode="true",
        LOG.std(nil, "info", "DemoItem", "a new block is registered");
    return xmlRoot;

Run Command

If you are inside a 3D world, one can call script using the SpawnPoint item.

Create Win32 TitleBar

Sometimes, we need to hide the native win32 title bar and create our owner-draw title bar.


The following mcml v1 code will do the job. see also test code

<pe:container name="titleBar" alignment="_mt" style="width:0px;height:64px;background:url(Texture/alphadot.png)" >
    <div style="position:relative;float:left;margin:5px;">drag this title bar to move the native win32 window</div>
    <pe:container name="winButtons" alignment="_rt" style="position:relative;padding:5px;margin:5px;width:100px;background:url(Texture/whitedot.png)">
        <input type="button" name="toggleBtn" tooltip="press Z key to toggle" onclick="toggleTitleBar" value="ToggleTitle" class="button"/>
    <pe:hotkey name="2" hotkey="DIK_Z" onclick="toggleTitleBar" />
-- This line will allow the user to drag this container to move the window.
Page:FindControl("titleBar"):SetField("EnableClientTest", true);

function toggleTitleBar()
    local bShowTitle = ParaEngine.GetAttributeObject():GetField("ShowWindowTitleBar", true)
    ParaEngine.GetAttributeObject():SetField("ShowWindowTitleBar", not bShowTitle);

“DefaultContext” filter

Can be used to replace the default scene context in paracraft via paracraft mod interface.

local MySceneContext = commonlib.inherit(commonlib.gettable("System.Core.SceneContext"), commonlib.gettable("System.Core.MySceneContext"));
function MySceneContext:ctor()

function MySceneContext:mouseReleaseEvent(event)

-- when mod is loaded, register the filter
GameLogic.GetFilters():add_filter("DefaultContext", function(context)
   return MySceneContext:CreateGetInstance("MyDefaultSceneContext");
see also: TestMod for a working sample.

Client/Server GUI

In many occasions, one needs to click a button in client side world to display some GUI and send result to server. But it is not trivial to implement. The logic is very similar to traditional web browser. But one can think of paracraft as a 3D web browser and server. The server side database includes all blocks, NPCs, timelines, etc, which are shared (automatically synchronized) by all clients. However, each connected client has its own unique 2d/3d view into the server side database. For example, the changing of player positions automatically generate requests to fetch shared data from the server, so it is with GUI pages, except that the process is not automatic.

The process of CS GUI request is like below:

  • A client make a request to the server, such as clicking a button in 3d world, which will cause server side script to execute.
  • The server side script may send back the proper GUI page content or url to display such as via /runat @p command to just the requested client.
  • The client renders the GUI page to collect information from the user and send result back to server possibly via /runat @admin or other commands or messages.
  • The server updated its database, such as changing blocks, modifying NPC positions, and updating data properties, etc. which will automatically be synchronized with other connected clients.
  • To send a message from client to server: /runat @admin /any_command_here
  • To send a message from server to client: /runat @p /any_command_here
Example 1: Simple C/S GUI


Put /runat @p /tip hi, username inside a command block on server side. It will display a simple tip GUI whenever a client user clicks the button.

Alternatively, one can also put /runat @p /open test.html inside a command block on server side. It will display any mcml GUI page on the client computer who triggers the button. /open test.html can open mcml GUI page relative to world or root directory.

Example 2: Custom C/S GUI

Custom GUI code must be pre-installed on both client and server, such as via a paracraft mod interface. The following code must be run on both client and server.

-- register a new show GUI command 
GameLogic.GetFilters():add_filter("show", function(name, bIsShow) 
    if(name=="MyApp.TestCSGUI") then
               _guihelper.MessageBox("hello from custom gui", function()
                       GameLogic.RunCommand("/runat @admin /tip client pressed Yes");

Then put /runat @p /show MyApp.TestCSGUI inside a command block on server side as in previous example. It will display a message box GUI whenever a client user clicks the button, and if the user pressed OK, it will send a message back to the server.

Note: For security reasons, only the admin user can edit command blocks, some simple blocks like Sign and image block can be edited by both client and admin user. Changes to blocks are automatically applied to all connected client.

Chunk Generators

There can be many custom chunk providers deriving from this base class.

Virtual functions:
    Init(world, seed)
    GenerateChunkImp(chunk, x, z, external)
    PostGenerateChunkImp(chunk, x, z)


Synchronous generator

By default generator runs in the main thread, so that your generator can safely use all API. Simply derive from ChunkGenerator and overwrite GenerateChunkImp, and register the provider by name.

see FlatChunkGenerator.lua for example.

Asynchronous generator

Some generators may take a long time to compute and generate large number of blocks. It becomes impossible to run it in the main thread without dropping render frame rates. In such occasions, one needs to use asynchronous generator, which runs in one or more worker threads. Actually, you can turn your synchronous generator into asynchronous ones by simply overwriting IsSupportAsyncMode and GetClassAddress method.

If IsSupportAsyncMode returns true, the chunk provider will send each chunk request to one of the worker threads for processing (see SetWorkerThreadCount function). The worker thread picks up the request and recreate the chunk provider instance based on GetClassAddress in that thread and pass a fake in-memory Chunk object (see also Chunk.lua) to its GenerateChunkImp function. Finally it sends back the data in Chunk object in compressed binary format to the main thread, which will apply the chunk data to the real ChunkCpp object (see also ChunkCpp.lua) in the main thread. BTW, applying all chunk data to chunk column in one API may be one-hundred times faster than setting individual blocks in the chunk.

However, there is limitations of asynchronous generator. The GenerateChunkImp should only set or get chunk data based on the requested chunk only. It can not query or set entities or advanced information that is only available in the main thread. However, one can overwrite PostGenerateChunkImp to generate some add-on blocks/entities in the main thread, because PostGenerateChunkImp is always called for both async and sync mode in the main thread.

See NatureV1ChunkGenerator generator for example.

Programmatically Create Blocks

Remember everything in paracraft originates from an item. So strictly speaking, one needs to call item:TryCreate to create an item in Paracraft.

However, for very simple block based items, we offer other easier ways like command /setblock or BlockEngine:SetBlock(x,y,z,block_id, block_data, flag, entity_data).

Change Default Player Appearance

One can change the main player appearance after world is loaded using the Entity:SetMainAssetPath function or /avatar command.

Another way is to change the block_types.xml of the corresponding item’s model configuration, like below.

<block id="30002" name="player" text="主角" searchkey="" tooltip="" item_class="ItemNPC" icon="Texture/blocks/items/skull_steve.png" hp="100" respawn_time="300000">
    <model assetfile="character/CC/01char/char_male.x" skin="Texture/blocks/human/boy_blue_shirt01.png" ></model>

One can do this via filters when your application starts. Both x and fbx files are supported for assetfile.