16 Jan

16 bits COM Oddity

I can’t even pinpoint what a 16 bits COM Oddity really means, but I think the idea is therein, somehow. Previously, I explained how to code a simple a “hello, world” program using the DEBUG tool that was shipped with DOS. Revisiting this obsolete knowledge was unexpectedly fun. We’ll retrieve the hexadecimal version of “hello, world” (well, “hello, world!!”) from that post:

EB 13 0D 0A 68 65 6C 6C 6F 2C 20 77 6F 72 6C 64
21 21 0D 0A 24 B4 09 BA 02 01 CD 21 B4 00 CD 21

That’s all we need for our “hello, world!!” binary. 32 bytes exactly. We can create that file bit by bit but that’d be too excessive, I think. Let’s use the echo command instead. This is the full command I entered in my Windows 10 cmd.exe prompt:

echo|set /p="Ù‼♪◙hello, world!!♪◙$┤○║☻☺═!1└═!">hello.com

After that you’ll get a 16-bit COM, hello.com, that will display the “hello, world!!” message. Funny 🙂

What are those weird characters?

First a little explanation. We want our hello.com file to be, byte after byte, an exact representation of the hexadecimal sequence above presented. We’ll use cmd.exe commands to dump characters into the file and, if we choose our characters carefully in order to match the target hexadecimal values, we’ll end up with the exact representation we’re looking for. For instance, the first 2 bytes block, EB 13, is the “jmp 115” instruction. Then comes the newline (0D 0A), and so on. If we convert our hexadecimal to decimal, we get:

235 19 13 10 104 101 108 108 111 44 32 119 111 114 108 100 
 33 33 13 10  36 180   9 186   2  1 205 33 180   0 205  33

The first byte in hello.com must be EB, or 235 in decimal. In order to dump our characters from the command line, we’ll convert that decimal value to a character. I’m trying this on a Windows 10 (64-bits) machine, with cmd.exe using Code page 850 Multilingual Latin 1. In such code page, character 235 is Ù. And 19 is ‼. And, luckily, 13 is ♪ and 10 is ◙. Those two characters are especially important because they represent the carriage return and the line feed, respectively, and some shells won’t convert them to characters. However, happily, cmd.exe with my default code page will handle them as we need. To input those characters you can type the usual ALT + decimal value.

There are a few important things to notice:

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15 Jan

“Hello world” with DEBUG

Coding “Hello world” with DEBUG will be a blunt exercise on programming futility. Or an exercise on retro, old-school coding. More than two decades ago I used to code in x86 (Intel) assembly, almost daily. I remember the masochist approach to learning the opcodes and the hardware architecture. The famous RBIL (Ralf Brown’s Interrupt List) was, back then, my favorite “reference”. First painful steps were taken and first crashes happily followed. I remember trying to code, as expected, the traditional “hello, world!”, using a strange tool included in DOS, DEBUG.COM. I wrote a post about this “hello, world” with DEBUG.COM elsewhere, and yesterday I found the time to reread it: I verified, first with awe, then with horror, and finally, with relief, that I had almost completely forgotten how to code in assembly. So I’ll revisit this here, mostly as a self-imposed disciplinary measure, an exercise on programming, specifically, an exercise on programming futility. Heck, DEBUG isn’t even available on the Windows 10 machine I’m typing this on. However, DEBUG looked pretty cool back then: it could assemble, disassemble and dump hexadecimal output. You could create little programs, or inspect programs and peek memory areas.

Specifically what I want is to build a minimal “hello, world!” program using DEBUG.COM. I don’t have any use for this, but it comes as a “relaxing” post after several weeks focused on the release of “DragonScales 3: Eternal Prophecy of Darkness” on Steam and the localization of “DragonScales 5: The Frozen Tomb”. After we execute DEBUG.COM we’ll meet a prompt with a “-” symbol. Now we can input our commands. I want to assemble, i.e., I want to type assembly language instructions. The command for that is “a”, which might be optionally followed by a memory address. By default, instructions will be placed starting from CS:0100, so I’ll use that address. Equivalently, I could type “a 0100” or “a 100” to achieve the same result.

-a

Now we have to place the data in memory. For this little program I only need the characters for “hello, world!!”. Notice I want two “!!” at the end. That’s because I want the final program to occupy exactly 32 bytes; we’ll see the reason for this later on. I’ll use the pseudo-instruction “DB” to define our string. With DB I can neatly provide the string using ASCII values, like this:

 db "hello, world!!"

Those are 14 bytes. However, I want a prettier output, with a newline character before and after our string. A newline is in fact two characters: a carriage return (CR is ASCII 13) and a line feed (LF is ASCII 10). In hexadecimal, CR is 0Dh, and LF is 0Ah. OK. Now our DB would be modified to look like this:

 db 0d,0a,"hello, world",0d,0a

Those are 18 bytes. We are not done yet with our data. In order to effectively print the message to the standard output I’ll recur to the function 09h of INT 21h. Check RBIL D-2109. In short, I have to place the value 09h in register AH, and DS:DX should point to the beginning of our string. The function will print every character until finding a “$” character (i.e., “$” acts as the “zero” in null-terminated C strings). ASCII value of “$” is 36, or 24 in hexadecimal. Therefore, we modify our DB instruction again:

 db 0d,0a,"hello, world",0d,0a,"$"
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06 Jan

DragonScales 3 on Steam

We’ll begin 2020 by releasing our game DragonScales 3: Eternal Prophecy of Darkness on Steam. Here’s the game’s Steam widget:

Key features for the Steam version:

  • 150 levels.
  • Only for Windows platform.
  • 10 Steam achievements.
  • Languages supported: English, German, French, Dutch, Italian, Portuguese and Spanish.
  • Updated libraries.
DragonScales 3 on Steam
DragonScales 3 on Steam

DragonScales 3 was the first DragonScales game with Gravity Mode and falling skulls. Furthermore, the game showcases 5 boss battles combining a new gravity approach with the classic DragonScales tile-matching gameplay. DragonScales 3’s story is based on a sinister prophecy, the Eternal Prophecy of Darkness. There is a group of dark cultists who want this prophecy to come true. Their plan is to bring back Specktr to life. Specktr! The ultimate embodiment of malice! Rumor has it that Specktr, once resurrected, will grant immortality to his followers. One of such followers, incidentally, is the powerful Archmage Cedric. DragonScales 3 is also the first DragonScales 3 with references to a fantasy kingdom, the Gravity Kingdom.

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17 Dec

DragonScales: The Story of Archmage Cedric

This is the background story for the Archmage Cedric of the DragonScales games. If you have not played DragonScales 3 or DragonScales 5 yet, the following text contains several spoilers. All the art of DragonScales was created by our artist XKlibur: check her portfolio here.

Archmage Cedric
Archmage Cedric

The Archmage Cedric was one of the most powerful mages of the Gravity Kingdom. His command of the DragonScales magic was sublime, and that raised him to great glory and fame. Other mages of the kingdom respected and even feared him. In a sense, the Archmage Cedric was the epitome of success in sorcery and he achieved all he ever dreamt of. Once these men achieve all the things they want, their ambition grows even bigger, and they start bordering madness. This occured to Archmage Cedric. Suddenly, he started regretting his human condition, pitying himself for the weaknesses of his mortal vessel, the ugliness of pain, and then yearned for the absolute immutability of his body: he wanted to become an immortal.

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11 Dec

DragonScales 6 game: Solution for Level 5-8

Some players of the latest DragonScales game, DragonScales 6: Love and Redemption, have reached out to us asking about a solution for Level 5-8. That level might seem a bit intimidating at first look, but once you figure out the little tricks for several parts of the board you’ll agree it’s kind of easy. Let’s take a look at the initial configuration of the board.

DragonScales 6 game initial configuration of Level 5-8
Initial configuration

A typical DragonScales board. We have two goals only: capture the red and the green cross-scales. There are some novelties, though, specific to DragonScales 6: keys and doors. Cells with a door icon won’t accept scales on them, so you’ll first have to remove the doors. That means you won’t be able to clear the top-left red cross-scale, or the green cross-scale or activate the arrow until you manage to remove the respective doors. To remove a door just click on it, but you’ll obviously need to capture at least one key beforehand. To capture a key, just form a combination containing the cell with the key.

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08 Dec

Inversion of Control in Software Engineering

What is Inversion of Control in Software Engineering?

Inversion of Control in Software Engineering (IoC) is essentially a strategy for decoupling software components. Basically, the purpose of IoC is to remove unnecessary dependencies (couplings) which might reduce flexibility and elegance of a system’s design. The term Inversion of Control in Software Engineering might sometimes appear applied to different design contexts. It is a term that comes from the 70s, when bottom-up parsing was considered an inversion of top-down parsing. It has roughly continued to be applied in multiple contexts. Some people think Inversion of Control in Software Engineering is a design strategy. For others, it’s a design pattern. After some articles dealing with OpenGL, in this post we will briefly discuss this topic of Software Engineering.

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04 Dec

Render a Triangle with OpenGL

This post will discuss how to render a triangle with OpenGL. In the following, renderization of a triangle assumes modern OpenGL, i.e., the old, fixed-function pipeline is of no concern for us in this post, as we’ll be using OpenGL buffer objects and shaders.

A Simple Triangle

By following the tutorials in the previous posts (Setting up Eclipse CDT for OpenGL and the GLFW Example) we were able to create a minimal program displaying an empty window. Now we want to draw something with OpenGL on that window, specifically, a triangle. Why a triangle? Well, the geometric shape more frequently used to approximate surfaces is the triangle. Approximation of 3D surfaces in real-time graphics by means of simpler shapes is known as tessellation. For our tutorial purposes, a single triangle will suffice.

GPU Power

Modern GPUs are quite fast and can also have a considerable amount of dedicated memory. When rendering, we’d like for as much rendering data as possible to be read by the GPU directly from its local memory. In order to render a triangle with OpenGL we’ll need, obviously, to transfer the 3 vertices of the triangle to the GPU’s memory. However, we do NOT want our rendering to go like this:

  • read a vertex from our computer RAM
  • copy it to the GPU memory
  • let the GPU process that single vertex
  • and then repeat this whole process for the next vertex of the triangle.

Ideally, what we want is to transfer a batch of data to the GPU’s memory, copying all the triangle vertices, and then letting the GPU operate with this data directly from its local memory. In OpenGL we have the concept of Vertex Buffer Object (VBO) to represent these data placed on GPU’s memory.

The data to render the triangle in OpenGL

Normally, we think of a vertex as a point, which in 3D space leads to a representation with 3 coordinates, commonly designated by x, y and z. However, in this case I’d like to think of a vertex as a more abstract concept: a minimal data structure required to define a shape. Given a vertex, we can “link” attributes to it to further define our shape. Thereby, one of such attributes of a vertex can be its position (the “x, y, z values”.) Other attribute might be the vertex’s color. And so on. In this tutorial we will “link” two attributes to our vertices: position and color. For position we will have three coordinates, each a floating point value. If a float takes 4 bytes, then our position attribute would require 3 x 4 = 12 bytes. For the color attribute, we’d have 3 extra components, following the RGB model. Each color component would then take 4 bytes, and the color attribute would also require 12 bytes. In total, each vertex would take 24 bytes, 12 for its position attribute, and 12 for its color attribute.

Now we have to specify how to process these vertices.

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03 Dec

GLFW Example

Here I’ll briefly discuss a tiny GLFW example. Previously, I explained how to setup Eclipse CDT to work with OpenGL, using GLFW and GLAD. However, I instructed to copy-paste the example code on GLFW Documentation page, without providing any details. In the following I’ll present some code that you can add to the little project of our setup post, and will include GLAD initialization too.

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27 Nov

Setting up Eclipse CDT for OpenGL with GLFW and GLAD

What’s OpenGL?

OpenGL is an API to render 2D and 3D graphics. Remember that an API (Application Programming Interface) is an interface for interaction between components of a system. Typically, an API defines a set of functions, protocols and/or tools. I’ll skip the details about the client-server model, but OpenGL allows a client program to communicate with GPUs (Graphic Processing Units, e.g., your videocard) to achieve faster, hardware-accelerated rendering. That’s why OpenGL is a common topic in the game development scene.

OpenGL is focused on just rendering. It’s an API to write and read data from a framebuffer, and that’s it. It won’t handle user input, or sound playback, or loading a PNG image. It does not even have functions to create or close a window. We’ll need auxiliar libraries for all of that.

A minimal OpenGL window

So we want to build a minimal OpenGL application on Windows. We’ll create an empty window with an OpenGL context, using the GLFW and GLAD libraries. In the following, I assume we’re using a 64 bits version of Windows. I’ll also be relying on mingw-w64. In summary, these are our assumptions:

  • Windows operating system (64 bits.) Things will be a tad different for macOS and Linux users.
  • Eclipse CDT.
  • mingw-w64 to build GLFW from sources. Besides, our Eclipse CDT project will be compiled with the gcc version of mingw-w64.
  • GLFW and GLAD libraries.

What’s GLFW?

As told, OpenGL does not provide any facility to create a window, retrieve user input, create the OpenGL context, etc. These functionalities depend on the operating system. GLFW is a C library which provides a neat abstraction layer to handle all of this on several platforms. Notice that GLFW is focused on management of windows, OpenGL contexts, user input and time. It will not play sounds, or load images, etc.

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12 Nov

Compatibility of our games with macOS 10.15 Catalina

Recently Apple released an upgrade for macOS, Catalina 10.15, which finally dropped support for 32-bits-only apps. This essentially means that 32-bits-only games won’t run on macOS Catalina. Regarding IKIGames titles, this is the current status of our games on macOS:

  • DragonScales 1 to 5: if your purchased them on iTunes, they will run on Catalina. If you purchased them on other stores, they should also be playable, but we cannot guarantee it.
  • DragonScales 6 won’t be available on iTunes, but you can purchase it on Big Fish Games. That version runs on Catalina.
  • NagiQ 1 will not run on Catalina. NagiQ 2 might not run either. Currently we have no plans to make these games compatible with Catalina and later macOS versions.
  • The Rainbow Machine, if purchased on iTunes, will run. Again, if you purchased it on other stores, the game should also be playable, but we cannot guarantee it.

If you upgraded to Catalina, it should be possible to play 32-bits-only games by using a virtualization program. That way you could install macOS Mojave (or previous versions) and run your 32-bits-only games.

If you need further assistance, please contact us.