Knight Online Terrain (GTD format for 1299)

I want to talk a little bit about reading from binary files using C/C++ and the file structure for the Knight Online terrain files (i.e. files with the extension “.gtd”). To follow along you need two things:

  1. A C/C++ compiler, here I’ll be using Visual C++ (Community 2015)
  2. A 1299 terrain file, I’m using “karus_start.gtd” but any .gtd will work as long as it’s from the 1299 version of the game – however I’d recommend that you also use “karus_start.gtd” so that our number match up.

The basic concepts I’ll discuss here are valid for reading any of the Knight Online content files. Also, if a particular map spans multiple versions of the game (with each version varying in the file structure) you can use the data you know is required for the 1299 version (discussed in this post) to figure out what was added/removed in other versions. Therefore, even though we’ll be discussing the 1299 file format this information is relevant for cracking all versions of the Knight Online terrain files. Here I’ll be assuming you have little to no C/C++ knowledge. However, I am assuming you know general programming concepts and the difference between memory on the stack vs. memory on the heap.

First let’s read in the .gtd file.

The function  int main(int argc, char** argv) is the main entry point for the program.  #include "stdio.h" includes the declarations for all standard input and output operations.  char filename[] = "karus_start.gtd"; defines a variable name “filename” which is a pointer to an array of “char”s allocated on the stack.  FILE* fp = fopen(filename, "rb"); opens the file “karus_start.gtd” in the “read binary” mode. This means we will only be reading from (as opposed to writing to) the file and we wish to treat the contents of the file as if it were all binary data. The rest of the code here checks to make sure we successfully opened the file (printing an error if we were unable to open it) and immediately closing the file and exiting the program.

So far this program don’t do much. We are just opening the file (if it exists) and closing it. What we want to do is start reading in the contents of the file. We can’t read in the contents unless we know a little bit about how the terrain information is structured. So before we start read in all the binary information let’s take a moment to discuss the .gtd file at a higher level.

Having played the game you have probably noticed how the maps are broken up into these little squares.

Each of these rectangles is referred to as a “tile” and each tile is a 4×4 rectangle. The map data for a tile consists of four points in 3D space. In this coordinate system X and Z run along the floor and Y points up into the sky. Therefore, since we know that tiles are 4×4 rectangles, the X and Z coordinates for all the tiles on the map can be set just by knowing how big the map is (this will be important later because only the Y coordinate for these four points is stored in the .gtd file). The idea of a tile isn’t enough though, we also need the concept of a “patch.” A patch consists of a rectangle of 8×8 tiles. Patches carry absolutely no information about how the map should be rendered. Patches carry information for how the map should be updated and are useful for increasing computational efficiency. We eventually plan to have trees blowing in the wind or NPCs performing particular animations, etc. – it would be a waste of CPU power to have trees located on the opposite side of the map blowing in the wind when the player isn’t anywhere near them. Patches are useful for only updating objects which are close to the player.

Interestingly, the 1299 .gtd files start with an 4-byte integer which we do not know the function of (I’d guess it’s likely a version number).

An  int in Visual C++ is 4 bytes.  int iIdk; allocates the 4 bytes on the stack which we will use to store the first 4 bytes of the .gtd file.  fread(&iIdk, sizeof(int), 1, fp); actually reads 4 bytes from the file and copies them into the 4 bytes we have allocated. Next we read in the name of the map.

Here we are reading in another 4-byte integer, although this time it is the length of the map name. This integer tells us how many characters there are in the map’s name. Now we’ll read in the size of the map, set the number of patches based on the map size, and grab all the map data.

Based on the code we have looked at up to this point it should be relatively straight forward to understand what’s going on here. However, we haven’t talked at all about  _N3MapData , let’s take a look.

Each of the four points making up a tile has one of these map data structs.  fHeight is the Y coordinate for a point (remember we can get the X and Z coordinate based on how big the map is).  bIsTileFull is less straight forward but I believe it gets used when setting which textures to use for a particular tile (here I’m taking “full” to mean “stuff is covering this tile”). I would be interested to hear possible alternative theories about this. The rest of the variables are used for deciding which texture to blend together ( Tex1Idx and Tex2Idx) and how they should be oriented ( Tex1Dir and Tex2Dir).

Next we read in the patch information.

This simply gives us how high each 8×8 patch is and the radius of its bounding sphere. Next we’ll read in the grass information.

This information is used for rendering the grass which pops up out of the tile. Then we read in information about the textures which we will use for each of the tiles on the map.

m_NumTileTex is the number of textures which get used for this particular map.  NumTileTexSrc is the number of files from which all these textures will be loaded from.  SrcIdx is the index into the source name array for which this texture is located and  TileIdx is the index of this texture within the file. Basically the DTEX folder has a bunch of files in it and each of these files contains a bunch of textures put together one by one. In order to get one of these textures you first must know which file to look into and then how far into that file to look in order  to get your texture.

Here are the last few variables we need.

If you have a few rivers or ponds on the map then each files have to be loaded and looked through.

This is the basic structure of the 1299 .gtd file. If you would like all the code along with a simplistic OpenGL implementation of the rendering go here.

Using the N3PMesh converter

Knight Online uses an internal file format called “N3PMesh” to store a lot of the game’s item meshes along with other various game meshes. A lot of these files are located in the “Item” folder found within the game’s install directory. You can think of every object in the game has having its own 3D mesh. In order for a object to appear in game we need to first know all the vertex information in order to draw the object using a 3D rendering library (in KO’s case it would be the DirectX library). A lot of the details aren’t necessarily important for this article but sometimes players would like to modify the 3D meshes in order to change how the objects look in game. I’m going to show you how to do this using the N3PMeshConverter.

Using the converter it is possible to convert .n3pmesh files into .obj files (allowing you to modify the appearance of the game’s weapons) and it can convert .obj files (along with other various formats) into .n3pmesh files. All this allows for you to export objects from the game, modify those objects, and import the modified objects back into the game.

In order to export an object you first must convert the .dxt item texture to a .bmp/.png image file using the N3TexViewer. Next run the following command using the command prompt (Windows Start Menu -> Search Bar -> Type “cmd” -> Press Enter).

This command will convert the .n3pmesh for the basic bow into a .obj file. Using the .obj and image file you can easily load the KO mesh into a 3D mesh editor like Blender.


In order to import the .obj file back into KO’s .n3pmesh format (presumably after you have made your modifications) use the following command (again via the command prompt).

Simply paste the new .n3pmesh into the KO content folder and the newly modified weapons mesh will appear in game!


Getting setup with the OpenKO project

I recently made a video on how to get setup with the OpenKO source code and another video explaining the basic structure and history of the codebase. Feel free to take the time and get the code running! If you have any questions feel free to send me an email (

This second video explains a little about where the source code originates from and what major changes have taken place since I first started working on everything.

Kodev – Updating the UIQuestMenu

I recently made a video explaining how the quest menu GUI works for the game Knight Online. This is the first part in a two part series where we look at why these GUI components work the way they do and how we can use the GUI editor to help us to implement functionality for later versions. Part two for this series has already been recorded I just need to upload it! I hope to do that in the next week or so. If you have any questions or would like to suggest future topics for videos please email me at “”. Thanks!

EDIT: I was recently able to upload part 2! In the future I will try not to make the videos so long because they quickly become hard to upload.


SDL 2.0 Tutorial-06: Networking 3

In the last tutorial we setup a basic TCP server. In this tutorial we will start by modifying the server we setup and finish by writing a player client application. In order to write a client application with SDL 2.0 we will need a lot of the ideas which where presented in my first string of SDL tutorials (here). A lot of my personal preferences for setting up SDL have changed since writing those tutorials so instead of using code found within those tutorials I will be using a collection of C++ files I have settled into using (found here).

First let’s start with a few server-side modifications. Let’s start by adding a few extra packet flags:

Now we have a packet flag for starting and completing a quest, as well as a packet flag for getting the amount of time left until the quest is completed. Next we will update our server-side “RecvData” function:

What I have done here is removed the work this function was doing to grab the packet flag from the start of the incoming socket data. This is because when a socket is ready for us to process it may have several packets all lined together. Therefore the data buffer returned by “RecvData” may contain several packets depending on how quickly the client is sending packets to us; so any work “RecvData” does to grab the flag from the first packet doesn’t help us identify the packet flags for all the other packets possibly following the first. Therefore the extra work being done isn’t necessary at this level.

Next we will add a new function called “ProcessData.” This function will continuously run on each packet we find within the data buffer returned by “RecvData.”

This is where we do the work and grab the packet’s flag. Everything here should look similar to what we where doing before when the server found client sockets which were ready with information to be processed – except for the fact that we have added two extra flags. The “GETTIME” flag checks if the player is currently questing; if not then the time left on the quest is 0, otherwise the server sends the time left on the quest to the player. The other flag is the “QUEST” flag; this flag checks whether the client is currently questing and starts the quest if they aren’t currently in a quest.

The finial server-side update we make will be to the main processing loop. First let’s crank up how often we check for ready sockets:

If  num_rdy <= 0 then we do not have any sockets ready for processing so we enter the server’s idle tasks. Previously we were simply adding four wood to the client’s resource count continuously. This is quite a silly thing to do! Instead let’s check for whether a client has completed any quests and if so we’ll send out a quest completed packet and a wood update packet. In addition, we’ll continuously send out “GETTIME” packets to keep the client updated with the server’s timer.

And for the final server touch we’ll update the code which runs if there are sockets ready to be processed. Notice that how we handle the server socket (for new connections) isn’t changing but how we handle the client sockets is changing.

I am also keeping track of the number of packets which the server processes for each of the ready clients for debugging purposes. Now the client-side stuff isn’t that different when it comes to the network side of things. A lot of the helper functions we have server-side will have analogous client-server versions. Here is the client-side code in its entirety:

All the SDL graphics processing and input handling is being wrapped with the custom files I wrote and linked at the beginning of this post. If you find these posts helpful or would like me to dive deeper into a particular topic covered here please send me an email at “”.