fix(core): render a full-turn sector as a full circle
What the developer wrote
Authored by tychovrahe
fix(core): render a full-turn sector as a full circle
`fill_sector` normalizes both endpoints into <0..360), which maps a span
of exactly one turn onto a single value. The octant loop reads that as a
zero-width sector and skips all eight octants, and the centre pixel is
skipped as well, so the call draws nothing at all where a full circle is
meant.
Detect the span before normalizing and pin it to the full range. Only a
forward span counts, so the `start > end` wrap-around convention and every
partial sector keep their existing behaviour. Normalization still runs on
both endpoints first, so its bound assert is never bypassed -- an infinite
endpoint traps rather than silently becoming a circle.
Verified that (0,360), (0,720) and (-360,0) now fill all eight octants
plus the centre, while (0,90), (90,180), (0,359.64), (300,60), (36,108)
and the empty (0,0) are unchanged.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
[no changelog]
What changed, and why it matters
This is a UI graphics bug fix in the Trezor hardware wallet firmware. When drawing a circular progress indicator or pie-chart-like shape spanning a full 360 degrees, the code mistakenly treated it as an empty slice and drew nothing. The patch detects a full-circle span before normalizing the angles and forces it to draw all eight segments plus the center pixel. There is no direct security vulnerability here; it is a rendering correctness fix.
No security action required. Treat as a normal UI correctness fix and include in regular firmware release testing.
Security signals we found
No memory safety, cryptographic, or authorization issues present in the diff
Change is confined to UI rendering logic
No input from untrusted sources is processed beyond existing angle parameters
No changelog entry suggests developer considered this a routine bug fix
Evidence from the diff
The fill_sector method in core/embed/rust/src/ui/shape/canvas/common.rs normalizes start and end angles into [0,360). For an exact full turn (e.g., 0 to 360), both endpoints collapse to the same value, so the octant-based loop interprets the sector as zero-width and skips drawing. The fix computes full_turn = end - start >= 360.0 before normalization, then pins start to 0 and end to 360 when true. Partial sectors and backward wrap-around cases are preserved, and infinite endpoints still hit the normalization assert rather than silently becoming a circle. The change is purely about drawing completeness for full-circle sectors.
Changed components
core/embed/rust/src/ui/shape/canvas/common.rsTrezor firmware UI canvas renderingInspect captured patch +7 / −0
### core/embed/rust/src/ui/shape/canvas/common.rs
@@ -600,9 +600,16 @@ pub trait Canvas: BasicCanvas {
return;
}
+ let full_turn = end - start >= 360.0;
+
start = (360.0 + start % 360.0) % 360.0;
end = (360.0 + end % 360.0) % 360.0;
+ if full_turn {
+ start = 0.0;
+ end = 360.0;
+ }
+
let alpha = 255;
let alpha_mul = |a: u8| -> u8 { ((u16::from(a) * u16::from(alpha)) / 255) as u8 };
Why this scored 19/100
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