Following a suggestion on one of my recent YouTube videos I’ve been trying out Turbo Rascal Syntax Error (TRSE) for my Commodore 64 game development and first impressions are very positive. TRSE uses a Pascal style language which I have used previously at University, though I missed out on the famous Borland Turbo Pascal for the PC.
TRSE is a full integrated development environment with many helpful features to make your classic 8bit/16bit coding easier. I understand it was originally developed for C64 coding but it now supports many computer and console systems including the ZX Spectrum, BBC Micro, Commodore Amiga and MS-DOS.
Features include inline assembly language support for when you need that extra speed, large numbers of example code, code profiler to show you which routines or data are taking up the most space and some built in editors for graphics and maps. For the C64 there is specialist support for playing music SID files, raster interrupts for split screen effects or sprite multiplexing and many other features which I’ve not had the opportunity to explore yet.
Moving from CC65 which uses the C programming language, I’ve found some of my earlier code doesn’t work as expected (even when rewritten in Pascal) but with the examples provided I’ve managed to replicate the main code fairly easily and that’s before I consider any optimisations or the use of assembly language.
You can see me using TRSE below with some rough test code for Demon’s Isle.
One of the challenges of creating a CRPG for the Commodore 64 is deciding what sort of visual style I would like for the game. I’m working with an overhead view as I think that plays well to the C64’s capabilities and I’m a big fan of top down games such as the Ultima series and Legacy of the Ancients.
Ultima IV on the C64
Whilst my options with the C64 are more limited than modern machines, I still have many decisions to make on the visuals front (putting aside my lack of artistic talent for a moment).
The C64 has a number of display modes with a maximum screen resolution of 320 x 200 pixels (or 40 x 25 character cells) in a choice of 16 colours. If I’m willing to sacrifice the horizontal resolution of the display then I can increase the number of colours I can use in each 8 x 8 pixel “character” cell from 2 colours to 4 colours but this will double the horizontal size of each “pixel”. You can see this in the image below. You also have the choice of bitmap versus character modes. This is a big over simplification of the capabilities of the machine but will hopefully suffice for this post.
Gauntlet on the C64 – Illustrating the use of multi-colour mode (image from MobyGames)
Currently I’m using character mode to redefine the 256 character set with my own characters and then piece them together to build up maps on the screen. The player moves around the map and can move to other map sections when the end of the current map is reached.
If I required more colour in each character cell I could use multi-colour mode but this tends to make the graphics look more “chunky”. If I require more detailed graphics then I could use bitmap mode but at the cost of additional memory (8Kb for a full 320×200 screen).
One of the other challenges I’m facing is trying to make interesting displays with individual character cells which are only 8 x 8 pixels wide. Now the Ultima games and most CRPGs of the 1980’s typically used 4 character cells to build each of it’s map tiles, doubling the resolution of each tile but halving the number of tiles you can display on screen. The Ultima display also kept the party icon centred in the map display with the map being redrawn around the player after every move.
Combat in Ultima IV illustrating the use of 16 x 16 pixel tiles
One of the things I like about using the individual characters as tiles rather than 2 x 2 characters per tile, is that it allows me to display more of the map on screen at a time but at the loss of some graphical detail. I’ve started playing around with some of the redefined characters and colours in the CBM PRG Studio screen editor which is great for creating simple graphics and prototyping screen displays. Programming single characters as tiles is also a lot easier for me as well and will perform more smoothly in play.
Playing around with some redefined characters and colours to build an on-screen map
I’ve included a sample image above of my brief sketches so far. Regardless of what screen mode and tile size I eventually use I’m also likely going to use the C64’s sprites as a means of adding higher resolution images for the player character, NPCs and monsters. These have the benefit of being independent of the screen display so can have their own colours, hires or multi-colour mode option so can be used to add some further interest to the display.
Since my last post I’ve revisited the CC65 cross compiler which you can use to write C programs on 6502 based systems such as the Commodore 64, Apple II and Atari 8bit.
I had been using CC65 for a few months, sketching out the beginnings of a C64 CRPG but had run into problems managing the memory configuration required for custom graphics. I’d moved onto using CBM PRG Studio and programming in 6502 assembly code which meant my code ran very quick but I was finding was slowing down my development time compared to using C in the past.
Some simple C code for the Commodore 64
Now I’m not much of a programmer in any sense of the word but I probably have the most experience of using the C language overall so I was finding 6502 assembly language time consuming to use and my game development time is very limited and I’m not really trying to do anything fancy technically by the standards of C64 games.
There is a lot of documentation online for CC65 but I was lacking an example of how to do a simple custom character set and use code overlays for swapping code in and out of the C64’s 64K of memory from disk. Most of the famous CRPGs I grew up with such as Ultima and Alternate Reality use this method to make the most of the machine’s limited memory by modern standards. I just couldn’t get this to work and gave up frustrated.
I noticed this week that CC65 had been used to create some of the code in Ultima IV Remastered for the C64. After this I came across a CC65 example online that included both a custom character set and code overlays and worked out how to compile it with a custom linker file. This determines how the memory map for the program is set up and where any external data files or graphic data should go. Once I had this working it was relatively easy to load in my modified character set and recreate my map code in C, display it on the screen and have a player marker move around the example map. I also was able to automate my compilation process with a single key press from within Notepad++ and run the resulting program in the Vice emulator which felt pretty smooth.
A simple map with a (feeble) character graphic player to move around
The main reason I was originally attracted to CC65 was that I love the idea of using C and being able to then reuse the code on other 6502 based platforms as well as modern PCs and operating systems. CC65 also has special support for some systems including the C64 so that you reference the C64 hardware directly within your C code. As CC65 includes a full assembler in its tool chain, you still have the option of using assembly language within your C program where extra performance is needed and tweaking the generated code. I’ll post more about CC65 in a future post; where to get it and provide a brief example and possibly a video of how to do the things I was struggling with in the hope they help others get started.
