1/28/2026 at 7:00:42 PM
> Embedded-graphics includes bitmap fonts that have a very limited set of characters to save space (ASCII, ISO 8859 or JIS X0201). This makes it impossible to draw most of Ratatui's widgets, which heavily use box-drawing glyphs, Braille, and other special charactersYou have a bitmap display, you can just draw lines and stuff without needing to rely on font-based hacks.
by zokier
1/28/2026 at 7:20:31 PM
Sure, but that's beside the point.Text based graphics with fancy or custom fonts is just crazy efficient. That is exactly how we got the amazing graphics of The Last Ninja or Turrican on machines with less than 64KiB useable RAM.
Same for more modern embedded devices. If you constrain yourself to text you increase both runtime performance and your developer productivity.
by weinzierl
1/28/2026 at 9:40:00 PM
The same isn't true for modern embedded devices, they don't have tile rendering hardware. If you connect a i2c/SPI screen (SSD1306, ST7735), you write all the pixels on the screen (or pixels to some subregion of the screen), these screens do have a backing memory in them.So in order to draw a line, you will - objectively - have to copy/move more bytes if you approximate line with character symbols.
This isn't a big deal, but crazy efficient it is not.
All the efficiency when drawing on those screens mostly relies on how well you chain together DMA transfers to portions of the screen you want stuff to be drawn to, so that SPI transfers aren't blocking the CPU (that's assuming you don't have memory for a second full-screen buffer).
by Johanx64
1/28/2026 at 11:07:20 PM
SSD1306 is a bit in the middle. It's technically a 128x64 monochrome bitmapped display, but it's organized as eight 128x8 "rows", with each byte representing a single 1x8 group of pixels. That organization really favors being treated as either four or eight lines of text - trying to use it as a generic bitmap display gets awkward, because it's only addressable at the level of those 1x8 groups.ST7735 is more of a standard (color) bitmap display.
by duskwuff
1/28/2026 at 11:18:47 PM
SSD1306 is just 1KByte for a second buffer, so even a rather low-end MCU likely can spare that. And you'd absolutely just draw normal lines if you use a display like that.It's very easy to use it as a generic bitmap display, there's nothing awkward about packing 8pixels into 1 byte, and you can set the addressing mode (horizontal/vertial) to whatever you want, etc.
by Johanx64
1/28/2026 at 7:33:46 PM
It was crazy efficient on character or tile-based hardware. It makes no difference on bitmap displays, or rather adds some overhead.by orbital-decay
1/28/2026 at 7:52:19 PM
At the end of the day it's always pixels - alway has been [1] - and the efficiency of storing and blitting a small number of fixed size rectangles is hard to beat if you can get away with it.[1] Except for the early oscilloscope style vector displays maybe.
by weinzierl
1/28/2026 at 8:11:43 PM
No, this is technically not fully correct. Early text based display output systems were relying on special character generator hardware to generate the display signals producing the text on screen. Those systems did not have any means of generating arbitrary pixel patterns.by gmueckl
1/28/2026 at 8:22:46 PM
Do you have an example? All the 8-bitters I know drew the characters from memory, which was a character ROM per default but could be changed either with a screw driver or by bank switching some RAM in-place.EDIT: If you mean they were not copied in a frame buffer first, you are right. I should not have written 'blitting'.
by weinzierl
1/28/2026 at 8:32:14 PM
Maybe too old to be applicable here, but the TRS-80 Models I and III (and probably more models) had no way to address pixels. You had to use semigraphic characters to emulate larger blocks at sub-character resolutions. https://bumbershootsoft.wordpress.com/2022/01/28/touring-the...by awkwardleon
1/28/2026 at 8:30:14 PM
The character ROM was not read and processed by the CPU. The CPU set some bytes in video RAM, which served as indexes into the character ROM by the video output hardware.I believe on some systems there were some tricks that allowed some bitmap display by redefining glyphs. One example off the top of my head is The 8-Bit Guy's Planet X2, which can use text mode but with glyphs redefined to use for icons, units, terrain, UI, etc.
by LoganDark
1/29/2026 at 6:22:18 AM
I believe you are correct, VGA even had character rom, where 'individual pixels' were not drawn by the CPU itself, the software presented an array of indexes into the rom and the vga hardware itself blitted the characters onto the screen.by worthless-trash
1/28/2026 at 9:21:17 PM
I recommend reading the TV Typewriter Cookbook.by adiabatichottub
1/29/2026 at 12:38:20 AM
IBM PC / AT / PS/2 all had a separate text mode, with glyphs defined in character ROM or RAM. Read about CGA, EGA, VGA. So TUIs basically owned the place since mid-1980s when PCs became ubiquitous, until mid-1990s when Windows started to dominate.by nine_k
1/28/2026 at 8:52:04 PM
With character RAM you can still only have up to 256 unique 8x8 blocks on screen.by direwolf20
1/29/2026 at 7:33:14 AM
> which was a character ROM per default but could be changed either with a screw driver or byNo. Stop believing everything ChatGPT told you on this topic and DYOR. That's some bad hallucinations.
by numpad0
1/29/2026 at 3:04:59 PM
Actually a small flathead screw driver is a useful tool to pull an (EP)ROM from its socket. Been there, done that (80s/early 90s).Might be fun though to check with ChatGPT on how to use a screw driver in this context. :-)
by RetroTechie
1/29/2026 at 2:02:01 AM
kaypro & trs-80, just a couple I happen to know myself. There is no way I just happen to know about the only 2.by Brian_K_White
1/28/2026 at 8:20:38 PM
Character-based hardware only stores the characters and the grid instead of the full bitmap for the frame, which is very efficient memory-wise. Tile-based hardware (e.g. most console graphics chips in the 8/16 bit era) also had scrolling and layers, and was extremely memory-efficient as well. With bitmap displays you already store full frames.by orbital-decay
1/28/2026 at 8:29:17 PM
Sure. Maybe I should not have written 'blitting' when the rectangles are not copied from one memory location to another but end up directly on the screen.My original point that putting a fixed number of small and fixed rectangles on a screen is more efficient than line drawing still stands though.
by weinzierl
1/28/2026 at 10:14:08 PM
It's still wrong, though.Without dedicated sprite hardware it's not more efficient to read a byte from one place and write a byte to another than to write background bytes and write line colour bytes. DMA controllers on µCs won't save you: a character is usually something like 8x8 or 8x16 and displays are rarely more than 8 bit, so we're talking about DMA transfers of just 8 bytes each, and the overhead of setting them up more than offsets any efficiencies gained.
An 8x12 cell, for example, is 96 pixels to be transferred in 12 rows of 8 pixels. That's 96 reads, 96 writes, and (assuming an unrolled inner loop) 12 branches, to copy as a sprite. Or, it's 96 writes and 12 branches to clear, and (horizontal line) another 8 writes to draw, no branches.
When your graphics become too complex for simple drawing routines to handle them, they're probably also too complex for simple character ROMs, too.
by codebje
1/28/2026 at 11:04:24 PM
Depending on MCU, you can chain DMA transfers together, so you can have many small writes without extra CPU involvement per DMA transfer. DMA channels are a limited resource however.There's quite a few ways to do this, you can do a DMA transfer per horizontal/vertical screen line (not enough memory for a fullscreen buffer, but usually enough memory for 2 fullscreen lines), with an interrupt which fills in the next line to be transfered, etc.
> displays are rarely more than 8 bit
Backing memory in these color TFT SPI displays is often 18bits per pixel, often transfered as RGB565 (2bytes) per pixel.
For SSD1306 its 1bit per pixel, and even the weakest MCUs usually have enough memory for a second buffer.
All this is completely ass-backwards thinking though. The crucial question is - does the end-user/customer want to see smooth lines or prefers "hacker-man" TUI aesthetics.
I'd say you generally speaking users want normal smooth lines graph instead of hackerman aesthetics.
So preferring implementation simplicity (TUI) might be another case where substandard programmers prioritize their convenience over the end-user needs/preferences.
by Johanx64
1/29/2026 at 10:28:54 AM
Without DMA you need to insert a lot of wasted cycles to wait between each SPI transfer, so it doesn't take that many bytes to make it worth it. I use variable width fonts on 16bit rgb565 displays and DMA doubles the speed of drawing text with ~20 bytes/characters.by lizzylot
1/28/2026 at 7:42:49 PM
Are you claiming that scrapping together boxes and whatnot with line drawing characters is more efficient than just drawing the lines directly?by zokier
1/28/2026 at 8:38:40 PM
I think they're claiming that having character-based pipelines and algorithms can be more efficient than doing everything on the level of pixels... I can't help but feel there's a middle-ground somewhere, though.by LoganDark
1/29/2026 at 11:29:48 AM
For simple SPI displays it's the transfer bandwidth that dominates, so for best performance you wanna minimize the number of pixels you need to send. So for eaxmple: if you wanna draw a 100 pixel long horizontal line, if you ever send more than 100 pixels of data you're not gonna hit the speed of light. And if you wanna draw an angled line you're gonna have to do something like bresenham and pixel by pixel because drawing NxN blocks for a 45 degree line would be insane.by lizzylot