Description
Overview
The goal of this assignment is to get you familiar with the GBA environment and to develop a small
GBA game. If you have not already, you will need to install several packages: cs2110-tools cs2110-
tools-emulator. More information can be found on T-Square in Resources / GBA / GBA tools
installation instruction.htm
Part 1
It’s time to create a library file for your GBA game. You will be using sets of these files to create your
games for the next few assignments. Please keep the following in mind: We are going to create two .c
files: a main.c and a mylib.c The purpose of the main.c file is to write all of your game logic. For
instance, you may have a neat function that will initialize all of the bricks’ locations for a breakout
game; this would go in your main.c file. Other useful functions that would apply to any game you
could write, for example, a function that draws a rectangle on the screen would go in mylib.c. Please
keep your files organized, as it will make your TA happy.
In addition, if you do not understand a concept, then you should be reading the required C book for
this class. We will be moving quickly through this stuff and if you fall behind your grade will hurt.
Terms you should know by the end of this assignment are italicized.
We will be creating the following files: mylib.c and main.c
We will be using a slightly modified version of this mylib.c for your next assignment.
mylib.c
Please add the following pre-processor declarations to this file:
• u16 – This will be an alias of the unsigned short type. You don’t want to type unsigned short all
of the time so you should use typedef to make u16 an alias of unsigned short, e.g. you could
write u16* videoBuffer instead of typing out unsigned short* videoBuffer.
• videoBuffer – A global variable pointing to the start of video memory. This is located at
0x6000000 and should point to a u16.
• Function prototypes – for each function you have to declare in mylib.c. These should be
located above the actual function implementations. These are forward declarations of functions
without defining them, so the compiler knows their signature ahead of time. You will see in
Part 2 why this is useful.
• Functions – You need to implement these three functions. (You may switch row and column
with x and y. I personally prefer (x, y), Bill likes (r, c)).
• // A function to set pixel (r, c) to the color passed in.
void setPixel(int r, int c, u16 color)
{
// @todo implement 🙂
}
• // A function to draw a FILLED rectangle starting at (r, c)
void drawRect(int r, int c, int width, int height, u16
color)
{
// @todo implement 🙂
}
• // A function to draw a HOLLOW rectangle starting at (r, c)
void drawHollowRect(int r, int c, int width, int height,
u16 color)
{
// @todo implement 🙂
}
Part 2
main.c
For main.c, we will need to include a few declarations as well. Notice that some of the following
declarations are duplicates from the mylib.c file. In your next assignment, we will be using header
(.h) files which allow you to remove much of this redundancy. If you know how to use header files,
feel free to go ahead and implement a mylib.h file, but this is not required for the assignment.
• REG_DISPCNT – The display control register, located at 0x4000000. This will be a symbol
that will access the memory location 0x4000000 and get the unsigned short located at
0x4000000 for us.
• RGB – A macro you should #define at the beginning of your file. This macro takes three
integers representing the red, green, and blue components of the color and returns the
corresponding color value. Your macro should work in all cases e.g. RGB(2+2, 4+4, g+2) and
should respect order of operations, based on the examples from class!
• u16 – This will be an alias of the unsigned short type. You don’t want to type unsigned short all
of the time so you should use typedef to make u16 an alias of unsigned short.
• videoBuffer – The global variable videoBuffer declared in mylib.c should be visible in any
file that needs to use it. To do this, extend the scope of videoBuffer to main.c by using the
extern keyword when referring to the variable from inside main.c.
• Function prototypes – for each function you had to declare in mylib.c. This is so the
compiler knows how to link between mylib.c and main.c.
• A main function as defined below:
int main(void)
{
// Put your code here
}
In your main function you should set up REG_DISPCNT as shown in class.
Remember that we want mode 3 and to enable background 2.
You will then have a busy loop somewhere in your code to keep the program from exiting. For
example, you could use while(1).
Your game should accept button inputs and react in some way, as was demonstrated in lecture. The
button layout is as follows:
GameBoy | Keyboard
——–|———-
Start | Enter
Select | Backspace
A | Z
B | X
L | A
R | S
Left | Left Arrow
Right | Right Arrow
Up | Up Arrow
Down | Down Arrow
Additionally, holding the space bar will make the emulator run faster. This might be useful in testing,
but the player should never have to hold down space bar for the game to run properly and furthermore
there is no space bar on the actual GBA.
You can learn more about button inputs on this site: http://www.coranac.com/tonc/text/keys.htm
Your Goal:
The goal of this assignment is for your to make a small game. This is one of the most open-ended
assignments for this course, and so there are many options available to you. Please do not make Pong.
After implementing the functions above, and working on the button input, you will have a toolkit for
drawing to the screen and interacting with the program. You can then do anything you would like, as
far as a game goes.
Your game needs to satisfy the following requirements:
1) You should use Structs to display at least three different objects on the screen at once.
2) You should implement some form of object collision.
3) The display for the GBA needs to change and update as the state of the game progresses.
4) Button input should visibly and clearly affect the flow of the game.
5) Use of text – use the example files that were provided for you during lecture.
6) There needs to be a sense of progression – it should be clear that the game is going
somewhere.
7) Try to avoid tearing of the image – implement a function that waits for vBlank, as was
demonstrated in lecture, to make the game run smoother.
8) Include a readme.txt file with your submission that briefly explains the game and the controls.
Warning
Two things to note for now
1. Do not use floats or doubles in your code. Doing so will SLOW your code down GREATLY.
The ARM7 processor the GBA uses does not have a Floating Point Unit which means floating
point operations are SLOW and are done in software, not hardware. If you do need such things
then you should look into fixed point math (google search).
2. Do not do anything very intensive, you can only do so much before the GBA can’t update the
screen fast enough. You will be fixing this problem in the next assignment.
I STRONGLY ADVISE that you go ABOVE AND BEYOND on this homework. PLEASE do not
make Pong – such submissions will lose points. Draw something amazing, or implement something
really cool! In the next assignment you will be making a more complex game for us to play. The more
you do now the better off you will be. Also, even though your submission will not be graded on its
creative properties, you are still more likely to make your TAs very happy and have a better
demo/grade if you go above and beyond what is required.
You may research the GBA Hardware on your own. You can read tonc (available at
http://www.coranac.com/tonc/text/), however you may not copy code wholesale from this site. The
author assumes you are using his gba libraries, which you are not.
If you want to add randomness to your game then look up the function rand in the man pages. Type
man 3 rand in a terminal. Lastly if you want to use an image (from the internet) in your submission,
you may download and install CS2110ImageTools.jar (also available in Resources / GBA). This
program will take an image and convert it into an array of colors for you to draw on the screen.
However, this will require knowledge of header files and multiple C files. We will get to all of this
in the next assignment, but it is great to look ahead to those things and try them out in this
homework.
Part 3 – Makefile
The makefile is a file used by make to help build your gba file. Normally you would use gcc directly to
compile you C programs. However the compiling process to make a .gba file is a little complex for you
to compile by hand. This is why we have provided for you a Makefile that will compile, link, and run
your program on the emulator with one little command “make vba”.
However the only thing that you must do is set up our Makefile to build your program. So you
must edit the Makefile and change the PROGNAME and OFILES to compile your program. Quick
summary of what you must do
PROGNAME should be the name of the generated .gba file. EXAMPLE HW8.
OFILES should be a list of .o files (space separated) needed to be linked into your gba file. For each .c
file you have put it in this list and replace the .c extension with .o. EXAMPLE main.o lol.o hi.o
To use the Makefile, place it in the same folder as your other game files, open a terminal and
navigate to the directory where the Makefile is and then execute the following command
make vba
Alternatively you can execute this command to use wxvbam (another GBA emulator)
make wxvba
Debugging
The cs2110- tools-debug package allows you to print things to the terminal from within a gba
game. (Remember that the GBA does not have a terminal to print things to).
I have enabled this functionality, by modifying the emulator’s source code. To use this functionality
here are the steps.
1. #include
2. Use the Macro DEBUG_PRINTF(format_string, varags) to print using a format string
3. Use the Macro DEBUG_PRINT(string) to just print a string out.
4. Examples. DEBUG_PRINTF(“My age is %d”, 25); DEBUG_PRINT(“HELLO WORLD”);
5. To compile your code with debugging support you must type the following (6-7) in the
terminal
6. make clean
7. make debugvba (or make debugwxvba)
8. [IMPORTANT] When you are done debugging type 9. into a terminal
9. make clean && make vba
10. Don’t forget to do step 8. If you do forget, then you will still be running the debug version.
Likewise, if you fail to type the command in 6 you will still be running the non-debug version.
DO NOT CALL PRINTF DIRECTLY FROM GBA CODE. USE THE MACROS DEBUG_PRINTF
AND DEBUG_PRINT.
Deliverables
main.c
mylib.c
Makefile (your modified version)
and any other files that you chose to implement
readme.txt (briefly explain the game and the controls)
Or an archive containing ONLY these files and not a folder that contains these files. DO NOT
submit .o files as these are the compiled versions of your .c files
Note: make sure your code compiles with the command
make vba
Make sure to double check that your program compiles, as you will receive a zero (0) if we
have to grade your homework past the demo period, and we are unable to compile your
program.
Good luck, and have fun!
