GBDK Programming Sample

In the previous post, we checked out GBDK Programming Setup. The GBDK is a cross-platform development kit for sm83, z80 and 6502 based gaming consoles including the Nintendo Game Boy and Game Boy Color.

Using the GBDK, it is now possible to write game code using the C language rather than pure Z80 assembly. Therefore, we would like to extend this knowledge and checkout some code samples and homebrew games.

Let's check it out!

Software
Follow all instructions from the previous post: this documents how to setup all the pre-requisite software.
Note: ensure you have downloaded and installed the GBDK devkit and Small Device C Compiler [SDCC].

Examples
As per the previous post, after the GBDK has been downloaded, installed and setup, we should now checkout C:\gbdk\examples\gb to learn more about APIs available in the devkit. Replicate prior Hello World example.

Launch Visual Studio 2015. File | New | Project... | Visual C++ | Win32 | Win32 Project

Name:	Game
Location:	C:\apa_image
Create directory for solution	UNCHECKED

Copy over all original folders and files from the corresponding example. Copy from prior Hello World example the hidden .vscode folder and files. Copy also build.bat and align with source compile.bat file. Add relevant files to Visual Studio 2015. Press Ctrl+1 to build, link and run code similar to the prior Hello World example!

Launch Visual Studio Code. Open example folder. Set breakpoint in main.c. Press F5 to debug step thru code


Here is the complete list:

CUSTOM: apa_image  SOURCE: apa_image  CUSTOM: banks  SOURCE: banks  CUSTOM: bcd  SOURCE: bcd  CUSTOM: colorbar  SOURCE: colorbar  CUSTOM: comm  SOURCE: comm  CUSTOM: crash  SOURCE: crash  CUSTOM: dscan  SOURCE: dscan  CUSTOM: filltest  SOURCE: filltest  CUSTOM: galaxy  SOURCE: galaxy  CUSTOM: gb-dtmf  SOURCE: gb-dtmf  CUSTOM: gbcompress  SOURCE: gbcompress  CUSTOM: incbin  SOURCE: incbin  CUSTOM: irq  SOURCE: irq  CUSTOM: isr_vector  SOURCE: isr_vector  CUSTOM: large_map  SOURCE: large_map  CUSTOM: lcd_isr_wob  SOURCE: lcd_isr_wob

CUSTOM: linkerfile  SOURCE: linkerfile  CUSTOM: metasprites  SOURCE: metasprites  CUSTOM: paint  SOURCE: paint  CUSTOM: ram_function  SOURCE: ram_function  CUSTOM: rand  SOURCE: rand  CUSTOM: rpn  SOURCE: rpn  CUSTOM: scroller  SOURCE: scroller  CUSTOM: sgb_border  SOURCE: sgb_border  CUSTOM: sgb_multiplay  SOURCE: sgb_multiplay  CUSTOM: sgb_pong  SOURCE: sgb_pong  CUSTOM: sgb_sfx  SOURCE: sgb_sfx  CUSTOM: simple_physics  SOURCE: simple_physics  CUSTOM: sound  SOURCE: sound  CUSTOM: temp_minimal  SOURCE: temp_minimal  CUSTOM: temp_subfolder  SOURCE: temp_subfolder  CUSTOM: wav_sample  SOURCE: wav_sample

Samples
Gaming Monsters YouTube channel has many samples to teach how to develop your own GameBoy games:

Launch Visual Studio 2015. File | New | Project... | Visual C++ | Win32 | Win32 Project

Name:	Game
Location:	C:\SimpleSprites
Create directory for solution	UNCHECKED

Copy over all original folders and files from the corresponding example. Copy from prior Hello World example the hidden .vscode folder and files. Copy also build.bat and align with source's make.bat file. Add relevant files to Visual Studio 2015. Press Ctrl+1 to build, link and run code similar to the prior Hello World example!

Launch Visual Studio Code. Open example folder. Set breakpoint in main.c. Press F5 to debug step thru code


Here is the complete list:

CUSTOM: helloworld  SOURCE: helloworld  CUSTOM: simplesprites  SOURCE: simplesprites  CUSTOM: movesprites  SOURCE: movesprites  CUSTOM: background  SOURCE: background  CUSTOM: window  SOURCE: window  CUSTOM: sound  SOURCE: sound  CUSTOM: noise  SOURCE: noise  CUSTOM: simplejumping  SOURCE: simplejumping  CUSTOM: metasprites  SOURCE: metasprites  CUSTOM: spritecollision  SOURCE: spritecollision  CUSTOM: bkgdcollision  SOURCE: bkgdcollision

CUSTOM: splashscreens  SOURCE: splashscreens  CUSTOM: fadeeffects  SOURCE: fadeeffects  CUSTOM: keyboard  SOURCE: keyboard  CUSTOM: savename  SOURCE: savename  CUSTOM: colorsprites  SOURCE: colorsprites  CUSTOM: backgrounds  SOURCE: backgrounds  CUSTOM: makingmusic  SOURCE: makingmusic  CUSTOM: spritetricks  SOURCE: spritetricks  CUSTOM: scrolling  SOURCE: scrolling  CUSTOM: debugging  SOURCE: debugging  CUSTOM: platformer  SOURCE: platformer

Homebrew
Larold's Jubilant Junkyard is a website/blog/shop which focuses on creating digital products including game development projects and tutorials. The Nintendo GameBoy development tutorial series is very educational.

Follow Larold's Jubilant Junkyard YouTube video channel for additional GBDK 2020 information and content:

SCREEN resolution	20 x 18 tiles	160 x 144 pixels
BACKGROUND	32 x 32 tiles	256 x 256 pixels

Compiler flags

-Wm-yc	GameBoy Color compatible	NB: lowercase c
-Wm-yC	GameBoy Color only	NB: uppercase C
-Wm-ys	Super GameBoy compatible

GameBoy Color Tile Attributes

Bit 7	priority flag	0: tiles below sprites, 1: tiles above sprites
Bit 6	vertical flip	0: tiles normal, 1: flipped vertically
Bit 5	horizontal flip	0: tiles normal, 1: flipped horizontally
Bit 4	not used
Bit 3	character bank specification	0: tiles at bank0, 1: tiles at bank1
Bit 2	see bit 0
Bit 1	see bit 0
Bit 0	bits 0-2	indicate tile color palette assignment

Launch Visual Studio 2015. File | New | Project... | Visual C++ | Win32 | Win32 Project

Name:	Game
Location:	C:\AlleywayGameboy
Create directory for solution	UNCHECKED

Copy over all original folders and files from the corresponding example. Copy from prior Hello World example the hidden .vscode folder and files. Copy also build.bat and align with source's make.bat file. Add relevant files to Visual Studio 2015. Press Ctrl+1 to build, link and run code similar to the prior Hello World example!


NOTE: ensure that the GBDK header files are included for Intellisense: Right click project | Properties |
Configuration Properties | C/C++ | General | Additional Include Directories | %GBDK_WIN%/include; $(SolutionDir)/headers/gen; $(SolutionDir)/headers/main; %(AdditionalIncludeDirectories).

Here is the complete list:

CUSTOM: alleyway  SOURCE: alleyway  CUSTOM: flappy-bird  SOURCE: flappy-bird

CUSTOM: pacman  SOURCE: pacman  CUSTOM: space-invaders  SOURCE: space-invaders

Summary
Armed with all this knowledge, we are now in an excellent position to build complete video games for the Nintendo Game Boy and Game Boy Color. In the interim, we see the GameBoy Competition 2023 is here!

GBDK Programming Setup

In 2017, we checked out devkitSMS Programming Setup to build 8-bit video games for Sega Master System. Here we installed all the tools required including a powerful emulator: Emulicious to test the video games.

Emulicious is a free multi-system emulator popular for Sega Master System and Sega Game Gear games but can also play Nintendo Game Boy and Game Boy Color games. Therefore, let's leverage Sega Master System development setup to build and test games for Nintendo Game Boy and Game Boy Color using the GBDK.

Let's check it out!

GDDK
The GBDK is a cross-platform development kit for sm83, z80 and 6502 based gaming consoles including the Nintendo Game Boy and Game Boy Color. It includes libraries, toolchain utilities and SDCC C compiler suite.

Software
Follow all instructions from the previous post: this documents how to setup the pre-requisite software.

Here is a summary of all required software to be installed:

Name  Version  C IDE Editor  Visual Studio 2015  C IDE Editor  Visual Studio Code  Cross compiler  Small Device C Compiler

Name  Version  Make files  Cygwin  Emulators  Emulicious, BGB  Debugger  Emulicious Debugger

Note: this post documents how to download and install SDCC v4.1.0 on both Windows and Linux.

GBDK
Navigate to the gbdk-2020 repository on github: gbdk-2020 has full instructions here. Download the latest release from gbdk-2020 archive e.g. gbdk-4.1.1 or git clone latest source code. Extract code into C:\gbdk.

Setup the following environment variable for GBDK_WIN as it can be useful throughout GBDK development. Add the following one environment variable: System | Advanced system settings | Environment Variables:

Variable	Value	Description
GBDK_WIN	C:\gbdk	Windows path format

Example
As an example, let's write a simple program that prints Hello World to the screen using the GameBoy DevKit. Create new directory: C:\HelloWorld. Create new file main.c. Copy in the following code to print Hello World.

main.c

#include <gb/gb.h>
#include <stdio.h>

void main()
{
	printf( "HELLO WORLD" );
}

Build
Manually compile and link the Hello World program. Launch command prompt: Start | Run | cmd.


Change directory cd C:\HelloWorld. Next, execute the following 2x commands (in bold):

ACTION	COMMAND	OUTPUT
Compile	%GBDK_WIN%/bin/lcc -Wa-l -Wl-m -Wl-j -c -o main.o main.c	main.o
Link	%GBDK_WIN%/bin/lcc -Wa-l -Wl-m -Wl-j -o output.gb main.o	output.gb

Finally, type output.gb. The Hello World program should launch in the Emulicious emulator.
Congratulations! You have just written your first test program using the GameBoy DevKit.

IMPORTANT
If game does not initially render correct then select Options menu | System | Game Boy or Game Boy Color.

Automate
Let's automate the build process: create C:\HelloWorld\build.bat script file that contains the commands:

@echo off
%GBDK_WIN%/bin/lcc -Wa-l -Wl-m -Wl-j -c -o main.o main.c
%GBDK_WIN%/bin/lcc -Wa-l -Wl-m -Wl-j -o output.gb main.o
output.gb

Visual Studio 2015
Similar to Sega Master System development using devkitSMS, setup Visual Studio 2015 as per instructions here. Also, follow instructions here to connect Ctrl+1 hot key to automatically compile, link and run code.

Launch Visual Studio 2015. File | New | Project... | Visual C++ | Win32 | Win32 Project

Name:	HelloWorld
Location:	C:\
Create directory for solution	UNCHECKED

Application type:	Console application
Additional options:	Empty project CHECKED

Navigate to C:\HelloWorld. Add existing: main.c and build.bat at the same folder level as HelloWorld.sln.


Finally, ensure that the GBDK header files are included for Intellisense: Right click project | Properties |
Configuration Properties | C/C++ | General | Additional Include Directories | %GBDK_WIN%/include.

Press Ctrl+1 to build, link and run!


Visual Studio Code
Similar to Sega Master System development using devkitSMS, setup Visual Studio Code as per instructions here. Add hidden .vscode folder + include tasks.json and launch.json files beneath to build + debug code.

Launch Visual Studio Code. Open folder C:\HelloWorld. Add the .vscode folder the following files beneath:

c_cpp_properties.json

{
  "configurations": [
    {
      "name": "stevepro",
      "intelliSenseMode": "clang-x64",
      "includePath": [
        "${env:GBDK_WIN}/include"
      ],
      "cStandard": "c11",
      "cppStandard": "c++17",
      "browse": {
        "path": [
          "${workspaceFolder}"
        ],
        "limitSymbolsToIncludedHeaders": true,
        "databaseFilename": ""
      }
    }
  ],
  "version": 4
}

tasks.json

{
    "version": "2.0.0",
    "label": "build",
    "type": "shell",
    "windows": {
        "command": "./build.bat"
      },
    "presentation": {"echo": true, "reveal": "always", "focus": false, "panel": "shared", "showReuseMessage": false, "clear": true},
    "group": {"kind": "build", "isDefault": true},
}

launch.json

{
    "version": "0.2.0",
    "configurations": [
        {
            "type": "emulicious-debugger",
            "request": "launch",
            "name": "Launch in Emulicious",
            "program": "${workspaceFolder}/output.gb",
            "port": 58870,
            "stopOnEntry": false,
        }
    ]
}

Open main.c. Set breakpoint. Press Ctrl + Shift + B to build source code. Press F5 to debug step thru code:


In Emulicious, choose Tools menu | Debugger to be able to fully debug step thru the Z80 assembly code:


Summary
Now the GBDK has been downloaded, installed and setup, we should checkout C:\gbdk\examples\gb to learn more about the APIs available in the devkit + checkout some code samples and complete homebrew games. This will be the topic of the next post.