astroblast

This is a mini game created to explore possibilities of game programming on the Commodore 64. This game is written entirely in 6502 assembly language. Game specific code is in the root astroblast directory but code of a utility nature that could be used in other games was separated and put in the nv_c64_util directory where you will find lots of code and macros that are not specific to this program. Also, in the nv_c64_util_test repository you will find test programs for this utility code. This game was intended to be run on an NTSC version of C64. If running within an emulator such ase VICE you will want to configure it as such. It seems to run fine in PAL mode but as you would expect everything runs a little slower.

Overview

All the assembler code in this directory is written for Kick Assembler and in general the setup outlined in the main repository README.md. This program is a mini C64 game that uses the nv_c64_util code for various functionality. When the game is running it looks something like this.

Software Dependencies

There are no dependencies on libraries or game frameworks other than the nv_c64_util companion repository.

Building

To build the code in this repo you need you will need a development environment that includes the tools in the env_setup.md of this repo. You will also need to have the code from the nv_c64_util repository available and in a directory that is at the same level as the astroblast directory. To prepare your build environment in this way you can follow these instructions.

1. Setup build tools/environment per the instructions here: env_setup.md
2. Create empty directory on your development machine, we'll call it BASEDIR
3. Change dir to BASEDIR in a git capable shell on your
4. Clone the nv_c64_utils dependecy repo into BASEDIR with this command https://github.com/nealvis/nv_c64_util.git
5. Clone the astroblast repository repo while still in BASEDIR with this command https://github.com/nealvis/astroblast.git
6. Build astroblast from VS Code by opening the astroblast directory in VS Code and then open the file astroblast.asm. With the kick assemebler IDE Extension installed per the env_setup.md in the root directory of this repository you press F6 and the Extension will call kickassembler appropriately for all the files needed and produce astroblast.prg which is a C64 program file that can be loaded an run on a real Commodore 64 or in the VICE C64 emulator.

The product of the build is the single C64 program file astroblast.prg which will exist in the astroblast directory.

Running Astroblast

If running in the VICE emulator be sure that the emulator is set to NTSC. You can do this by selecting Settings from the menu, then Machine and Model. In this window you can select the settings shown in this screen shot:

To run astroblast in VICE it can be passed as the single argument on the commandline like this: x64sc.exe astroblast.prg

Alternatively if you would like to run it on a real C64 you can copy the file to a floppy disk (or SDCard if running an sd2iec device) and load it as normal with load "astroblast.prg",8 followed by Run to execute after its loaded.

Game Play

This is a two player game. There is no one player mode. The object of the game is to collect more asteroids than the other player before the time runs out or the target number of asteroids has been collected. Both options of playing for a duration vs number of asteroids and the game ending number of seconds or asteroids collected can be set in the opening title screen

Other options on the title screen include the following keys:

• < key: Turns the game master volume down
• > key: Turns the game master volume up
• E key: Sets difficulty mode to Easy
• M key: Sets difficulty mode to Medium
• H key: Sets difficulty mode to Hard
• S key: Sets the length of the game to end when Score is reached
• T key: Sets the length of the game to end when Time is reached
• - key: Decreases the length of the game.
• + key: Increases the length of the game

To play this game both joysticks are used. Joystick 1 controls the ship on the top of the screen as it moves left to right and joystick 2 controls the bottom ship. Both ships are always moving forward unless pushed back by some solar wind in the game. Players control the speed at which the ships move though.

There is a Turret on the far right of the screen halfway down. This turret has two guns, one shoots up and the other shoots down. The turret can only shoot while its armed. Players can see that the turret is armed and about to shoot because the guns will be flashing yellow and white. While the turret is armed either player can force it to fire by pressing the joystick fire button and only the gun pointed at the other player will shoot. If neither player fires while the turret is armed, it will eventually fire at both ships on its own. If a turret shoots a ship, that ship is stunned which turns it grey, and its pushed back to the far left until it can recover. While a ship is stunned it can not collect asteroids or be controled by the players joystick.

Game Points of Interest

Some interesting points regarding the way the game is put together follow.

Game Sound

The game sounds were created using GoatTracker v2.76. The main music for the game is in the file astro_sound.sng. When loaded into GoatTracker you will see that there are a few different subtunes that are used in the game including:

• Subtune 0: The main music that plays throughout most of the game
• Subtune 1: The music that plays during the winner screen once the game is over.
• Subtune 2: The music that plays during the title screen. The sound effects for the game are individual instruments created in GoatTracker. These files are loaded and edited separately in GoatTracker. Here are some of the sound effect files in the game:
• hole_sound.ins: The sound played when the blackhole appears in the game
• ship_hit_asteroid_sound_fx.ins: The sound played when a ship hits an asteroid
• silent_sound_fx.ins: a very short sound that is silence. This is only use as a way to interupt other effects that are playing.
• turret_fire_sound_fx.ins: is the sound that is played when the turret fires.

All the music and the sound effects files are in the astroblast/sounds subdirectory. The code that controls the music and sound is in the astro_sound.asm and astro_sound_macs.asm source files.

Game Music: astro_sound.sng / astro_sound.bin

The .sng file cannot be used directly within the game. This file must be converted to a binary file first and then the source code can import it directly at the right location. To convert the astro_sound.sng file to astro_sound.bin follow the following steps:

1. Start GoatTracker with this command goattrk2.exe -N the -N is for NTSC mode rather than PAL
2. Load the astro_sound.sng file using the F10 key. Note: you must have the cursor in the left pattern editing side of the program to load a .sng file. If the cursor is in the right instrument side of the program then it assumes you want to load an instrument (.ins) file. As an aside, once loaded, this file can be edited and then saved. To save it as a .sng file, use the F11 key and give it the name you want to save as.
3. Pack/relocate and save the file as a binary file for the program by pressing the F9 key while the cursor is in the table on the left side of the program
4. Select the playroutine options shown in this image (yes, yes, yes, no, no, no, no)
5. Select start address of $8000. This must match the address into which the binary file is imported in the assembly source.
6. Select zero page addresses of $FD and $FE. These are two unused zero page addresses. The Astroblast code may use these addresses but will save and restore their values when it does.
7. Select format to save in as Raw Binary Format (no start addresses)
8. Name the file. To stay consistant with the game code it should be named astro_sound.bin this file can then be directly imported into the assembly source code when its getting assembled.

Game Music: Adding a subtune.

Each .sng file can contain multiple subtunes. The game engine can then select an appropriate subtune to play (it repeats in a loop) at specific points of the game. When adding a subtune in GoatTracker:

• Put cursor in the order list in the upper right of the application
• Use < and > key to navigate to an unused subtune. Note that subtune 00, 01 and 02 are used. To add a fourth subtune use the > until you see CHN ORDERLIST (SUBTUNE 03, POS 01). Subtune 03 is the fourth subtune since they are zero based.
• Next you will need ot insert patterns for each channel into the order list. Do this by placing the cursor on the RST00 for the channel you want to add a pattern. If you want to use more than one channel for the subtune you'll need to insert patterns ino each channel you want to use. You can also use multiple patterns within a channel and they will be played sequentially.
• After patterns are added to the subtune's order list the patterns need to be created (unless you are reusing existing patterns). To see how patterns are created and edited look at the GoatTracker Documentation.

Game Sound Effects: *.ins / *.bin

To open, edit and save a sound effect for this game you can follow the steps below.

1. Start GoatTracker with this command goattrk2.exe -N the -N is for NTSC mode rather than PAL.
2. Open the .ins file. Each sound effect is saved as a GoatTracker instrument file (.ins file). With the cursor in right side of the application where instruments are edited press the F10 Key and select the .ins file to edit.
3. To hear the effect press the space bar with cursor on the right side of the screen. If needed, -space will stop the instrument from playing. When using an instrument as a sound effect there are lots of limitations which the GoatTracker manual spells out. Among others, all notes must be absolute, not relative. Also jumps causing a loop don't seem to work, instead the effect just ends at the jump.
4. To Save the .ins file press the F11 key and then set the filename and directory for the file to save.
5. Convert the .ins file to .bin by using the following utility that comes with GoatTracker ins2snd2.exe file.ins file.bin -b This will create the .bin file from the .ins file.

Sprites

The sprites for the game were create via the Spritemate web application here: https://www.spritemate.com/. To edit the sprites, load the file astro_sprites.spm from within the web application

Custom Charset

Astroblast uses a custom character set which was created using the charset editor in cbm prg studio. The project file for cbm prog studio is in the astro_charset_proj subdirectory. To see the custom charset, open the astro_charset_proj.cbmprj file in that directory from CBM prg Studio. Then double click on the astro_chars.cst to open the charset editor. To save the custom charset, in the character editor, export the charset to file. Include all characters in the charset and name the file astro_charset.bin. This file should be in the main astroblast directory.