For prior related work, check out patent US-6377261-B1 "Compiling glyphs into instructions for imaging for execution on a general purpose computer" filed 1996. The basic idea is each character turns into a sequence of "Load Immediate" / "Shift" / "OR to Memory" instructions; so there's no more fetching from a stored bitmap of the font, as the pixels are implicit in the Immediate data in the generated machine code. Then you can get fancy when one row of pixels is the same as the previous row in the character, so you don't even need to do the Load Immediate. Etc. This scheme was used in FrameMaker for Macintosh back in the day, as implemented by Gus Fernandez (who went hog wild on additional optimizations).
Image 6 (with figures 8 through 12) is fun; you can eliminate the Shift if you're willing to have multiple different JITed functions for each character, each one generated knowing what its shift count is, leading to yet more optimization opportunities.
Something like this was called "sprite compilation" and used a lot in the DOS game coding scene back in the day. The idea was, given a bitmap image of a sprite, produce the code that would draw that sprite on the screen in assembly and incorporate it into your game. Not very flexible, but fast and useful in the days when games had a lot of 2D bits and bobs moving around, especially for those who could not yet afford a 486 and were stuck on an old Tandy 1000 or something...
This is a really great project. So many retro computers are OP that they can use large frame buffers and programming to them doesn't feel like being close to the metal back like back in the day which was more intimate.
This implementation reminds me of two of my early experiences: programming display lists on Atari 8-bit and an HP PCL 5e interpreter (with short raster band buffer). I didn't really get into VCS/2600 128-byte beam racing but did do a fair amount of display-list-interrupt on-the-fly coding for homemade games and demos. I really thought the Atari Antic display list system was terrific--thanks to Jay Miner who also did the Amiga--and didn't see much like it again until OS/2 Presentation Manager or Java FX.
The PCL interpreter probably had the closest shape using a few hundred line cyclic buffer. It 'rendered' into y-sorted objects that needed to be later rendered/rasterized. Each object was cut to be at most 255 pixels (0.85") tall and used reverse max-y ordering since it couldn't be drawn until after the beam passed the wraparound scan line still rendering Y - buffer_height.
I've been building BASIC32, a retro BASIC interpreter for microcontrollers so I can flash it once and easily create lots of new projects.
What you give up with the authors approach is "read". The screen becomes write-only. There are only a few functions that require reads: getting a pixels current color and doing operations like flood fills or paints.
Because I was going for the retro feel of BASIC, I wanted to support these, so I opted for a frame buffer. It isn't as technically cool. On the RP2350, it does require low resolution and low bit rates because they often have RAM limited to KB.
If you step-up to the ESP32-S3 variants with 4MB or 8MB of RAM the frame buffer gets much easier.
This is cool, I did something similar with a CoreText replacement I've been building recently.
My code can JIT + render to the atlas faster at p100 than CoreText can render without the JIT at p50, and with better quality (measured against an exact cover reference).
The dot-product kerning trick is the bit I keep coming back to — encoding each glyph's edge profile as a bitvector and letting the overlap popcount decide the spacing feels like the sort of elegant hack that only falls out of genuinely understanding the problem. Also appreciated the honesty about the LLM-assisted parts; the cycle-count analysis is clearly hand-checked either way. I wonder how far the packed-font idea scales before the packing overlaps start costing more than they save.
For prior related work, check out patent US-6377261-B1 "Compiling glyphs into instructions for imaging for execution on a general purpose computer" filed 1996. The basic idea is each character turns into a sequence of "Load Immediate" / "Shift" / "OR to Memory" instructions; so there's no more fetching from a stored bitmap of the font, as the pixels are implicit in the Immediate data in the generated machine code. Then you can get fancy when one row of pixels is the same as the previous row in the character, so you don't even need to do the Load Immediate. Etc. This scheme was used in FrameMaker for Macintosh back in the day, as implemented by Gus Fernandez (who went hog wild on additional optimizations).
Permalink: https://patents.google.com/patent/US6377261B1/en
Image 6 (with figures 8 through 12) is fun; you can eliminate the Shift if you're willing to have multiple different JITed functions for each character, each one generated knowing what its shift count is, leading to yet more optimization opportunities.
Since he's not caching the JITted code anyway, might as well!
Something like this was called "sprite compilation" and used a lot in the DOS game coding scene back in the day. The idea was, given a bitmap image of a sprite, produce the code that would draw that sprite on the screen in assembly and incorporate it into your game. Not very flexible, but fast and useful in the days when games had a lot of 2D bits and bobs moving around, especially for those who could not yet afford a 486 and were stuck on an old Tandy 1000 or something...
This is a really great project. So many retro computers are OP that they can use large frame buffers and programming to them doesn't feel like being close to the metal back like back in the day which was more intimate.
This implementation reminds me of two of my early experiences: programming display lists on Atari 8-bit and an HP PCL 5e interpreter (with short raster band buffer). I didn't really get into VCS/2600 128-byte beam racing but did do a fair amount of display-list-interrupt on-the-fly coding for homemade games and demos. I really thought the Atari Antic display list system was terrific--thanks to Jay Miner who also did the Amiga--and didn't see much like it again until OS/2 Presentation Manager or Java FX.
The PCL interpreter probably had the closest shape using a few hundred line cyclic buffer. It 'rendered' into y-sorted objects that needed to be later rendered/rasterized. Each object was cut to be at most 255 pixels (0.85") tall and used reverse max-y ordering since it couldn't be drawn until after the beam passed the wraparound scan line still rendering Y - buffer_height.
I've been building BASIC32, a retro BASIC interpreter for microcontrollers so I can flash it once and easily create lots of new projects.
What you give up with the authors approach is "read". The screen becomes write-only. There are only a few functions that require reads: getting a pixels current color and doing operations like flood fills or paints.
Because I was going for the retro feel of BASIC, I wanted to support these, so I opted for a frame buffer. It isn't as technically cool. On the RP2350, it does require low resolution and low bit rates because they often have RAM limited to KB.
If you step-up to the ESP32-S3 variants with 4MB or 8MB of RAM the frame buffer gets much easier.
Added "race the beam" to my personal dictionary today :-). It's such a breath of fresh air to read something which is not written by an LLM.
You might find this[0] interesting.
[0]: https://mitpress.mit.edu/9780262539760/racing-the-beam/
Link is to a book recommendation, "Racing the Beam: The Atari Video Computer System" $27 paperback.
This is cool, I did something similar with a CoreText replacement I've been building recently.
My code can JIT + render to the atlas faster at p100 than CoreText can render without the JIT at p50, and with better quality (measured against an exact cover reference).
The dot-product kerning trick is the bit I keep coming back to — encoding each glyph's edge profile as a bitvector and letting the overlap popcount decide the spacing feels like the sort of elegant hack that only falls out of genuinely understanding the problem. Also appreciated the honesty about the LLM-assisted parts; the cycle-count analysis is clearly hand-checked either way. I wonder how far the packed-font idea scales before the packing overlaps start costing more than they save.