C64 Basic: Game Map Overhead “Camera View”

https://retrogamecoders.com/overhead-camera-view/

Comments

amiga386May 26, 2026, 3:41 PM
What you really need:

http://1amstudios.com/2014/12/07/c64-smooth-scrolling/

https://www.c64-wiki.com/wiki/Scrolling

* The top 4 bits of $D018 (VM10-VM13) control the base of graphics memory

* The bottom 3 bits of $D011 (YSCROLL) and $D016 (XSCROLL) let you delay screen display by 0-7 pixels in either axis

* The 4th bit of $D011 (RSEL) and $D016 (CSEL) let you shrink the screen viewport so it's visibly 304x192 pixels (in NTSC) even though the screen memory is still 320x200.

VM10-13 lets you establish a double-buffer, you can switch instantly between a front and back buffer by changing $D018. While you are scrolling, you copy the front buffer to the back buffer, offset by 8 horizontal pixels (1 byte) or 4 vertical pixels, then add in new map data on the edge you're scrolling towards. On each frame, you update XSCROLL/YSCROLL by one pixel so the visible screen is moving towards your new screen, then once it's moved all 8/4 pixels, switch to the new buffer.

The cost of copying all that graphics memory is expensive, so split it across the 8/4 frames.

bluescrnMay 26, 2026, 4:33 PM
Experimenting with C64 BASIC taught me a lot back in the day, but it quickly became clear that for any real game dev you need to be using assembly.

But a few years later, the Amiga brought us DPaint and Blitz Basic, and suddenly it was very possible to make a pretty competent game in BASIC as a self-taught teenager with no Internet access. That’s probably a better choice for anyone wanting to experiment with retro game dev using the tools of the period without resorting to assembly language

pjmlpMay 27, 2026, 6:48 AM
AMOS was also another beloved alternative on the Amiga.

Just cross-checked my memories, Worms was written in Blitz BASIC, another example of good ideas matter more than programming languages, assuming that it is good enough for the implementation.

I owe having learnt Timex BASIC, Turbo BASIC, AMOS, Turbo Pascal, Z80, 68000, and 80x86 Assembly, before learning C, to understanding it not being that special.

dspillettMay 26, 2026, 5:05 PM
That depends on what you mean by “real game dev”. I did a few game things of my own in BBC BASIC, eventually with a bit of 6502 assembly in key places, back in the day. On those machines you can still happily run a basic game loop in interpreted BASIC, the whole thing for text-based games, you just need to get down to the bare CPU for things like sprites, other rapid graphics drawing, and maybe some other number crunching (I did some basic compression in assembly for lots of text, though it wasn't really effective, if you are already doing graphics in assembly, then it probably makes sense to do collision detection and such there too, etc.).
egypturnashMay 26, 2026, 5:40 PM
C64 BASIC is kind of a mess, there's zero support for graphics and sound. Your code rapidly becomes a giant pile of POKEs and PEEKs, and all your operations become absurdly slow because all the math routines are floating point only, so there's a ton of integer/fp conversion overhead on something as simple as "peek a memory location, AND/OR it with a few values taken from variables stored as floating point, poke it back".

Assembly becomes really attractive really quickly.

WoansdeiMay 26, 2026, 8:21 PM
C64 Basic did have integers.

A floating point

A$ string

A% int

as you would expect ints are quicker.

izacusMay 26, 2026, 8:56 PM
Err, ints are internally stored as floats as well and that leads to some really interesting performance quirks where you'd not expect.

There were BASIC compilers for C64 which generated significantly faster code just because they actually used ints for integer operations.

bluescrnMay 26, 2026, 6:59 PM
BBC BASIC was far better than C64 BASIC.

It had a nice set of built-in graphics functions and an inline assembler, amongst other things.

I can still remember that VDU 23 was the command to redefine a character, so much easier than doing the same sort of thing on the C64 (copy the character set from ROM to RAM, get the VIC to use the RAM copy with POKE statements, modify the desired character)

simonhMay 26, 2026, 10:04 PM
C64 Basic was V2 of a dialect of the Microsoft derived Basic for the PET. It was out of date already compared to the latest V4 because the older version fit into a smaller ROM to save costs.
timbit42May 27, 2026, 12:46 AM
Sword of Fargoal and Pirates! were both almost entirely written in uncompiled BASIC.
bonziniMay 26, 2026, 2:55 PM
There's a lot that can be improved in the code, such as just using FOR...TO...STEP would be much faster.

In general, this is a routine that is super easy to write in 6502 assembly. Most magazine BASIC games had something like that, with a few such routines that were POKEd in memory at startup. Several were written in a relocatable fashion so that they could be copied easily from one game to the next.

pugworthyMay 26, 2026, 6:59 PM
Man does this bring back memories of my old Atari 800 and entering or writing games in BASIC for it. Something extremely nostalgic about that kind of development for some of us.