andygrove opened a new issue, #2013:
URL: https://github.com/apache/datafusion-ballista/issues/2013
## Describe the bug
The `ballista-cli` TUI banner renders as garbled characters / tofu boxes
rather than the "DataFusion Ballista" wordmark. Reported on macOS, but it will
reproduce almost anywhere.
Copying the garbled region out of the terminal yields characters like:
```
🬂██🬂🬎🬹🬠ðŸ¬ðŸ¬ðŸ¬ðŸ¬ ðŸ¬ðŸ¬¹â–ˆðŸ¬ðŸ¬ ðŸ¬ðŸ¬ðŸ¬ðŸ¬
```
Those are U+1FB02, U+1FB0E, U+1FB39, U+1FB2D — **sextants**, from Unicode's
*Symbols for Legacy Computing* block. Most monospace fonts do not include that
block, so they render as tofu.
## Root cause
`render_banner` in `ballista-cli/src/tui/ui/header/mod.rs` selects the
`tui-big-text` `PixelSize` by width, and every branch it can pick draws from
Symbols for Legacy Computing:
```rust
let banner_size = match area.width {
0..70 => PixelSize::Octant, // U+1CD00 octants (Unicode 16)
70..80 => PixelSize::QuarterHeight, // also U+1CD00 octants
_ => PixelSize::ThirdHeight, // U+1FB00 sextants
};
```
`tui-big-text` documents exactly this hazard on all three variants:
> *Note: depending on how the used terminal renders characters, the
generated text with this PixelSize might look very strange.*
The library's other pixel sizes (`Full`, `HalfHeight`, `HalfWidth`,
`Quadrant`) draw only from **Block Elements** (U+2580..U+259F), which is
universally supported — but none of them are reachable in the current code.
The reason the code ended up on the exotic sizes is the header height.
`ui::render` gives the header `Constraint::Length(6)` and the banner is two
lines, so each line gets 3 rows. Per `PixelSize::pixels_per_cell`, every size
that fits two lines into 6 rows is a legacy-computing one:
| PixelSize | cols/char | rows/char | glyph block |
|---|---|---|---|
| Full | 8 | 8 | Block Elements |
| HalfHeight | 8 | 4 | Block Elements |
| HalfWidth | 4 | 8 | Block Elements |
| Quadrant | 4 | 4 | Block Elements |
| ThirdHeight | 8 | 3 | Sextants |
| Sextant | 4 | 3 | Sextants |
| QuarterHeight | 8 | 2 | Octants |
| Octant | 4 | 2 | Octants |
So the 6-row header is the real root cause; the glyph choice is downstream
of it.
Note that picking a different font is not a viable workaround: the
`Octant`/`QuarterHeight` branches need U+1CD00, added in Unicode 16 (Sept
2024), which essentially no shipping font carries.
## To Reproduce
Run `ballista-cli` with the TUI on any terminal whose font lacks Symbols for
Legacy Computing (the common case) and look at the header.
## Expected behavior
The banner renders legibly using glyphs available in ordinary monospace
fonts.
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