Embed the stats decimal separator and damp the battery percentage

[Raffi1202]

Problem

Two OSD reports. #10420: on the post-flight stats screen, Flight Distance and Maximum Distance From Home use DJI number formatting on every video system, a separate . character that costs a column; the reporter notes it was never a regression, it always looked like this. #10053: the Battery Remaining Percentage element is sampled so often that its digits change constantly and the value never settles in flight (INAV 7.1.1, quadcopter).

Fixes #10420
Fixes #10053

Cause

src/main/io/osd.c:396, :408, :419 on maintenance-10.x: the three fractional branches of osdFormatDistanceStr() print "%d.%02d%c". osdFormatCoordinate() (osd.c:795) and osdFormatCentiNumber() only print an explicit dot on DJI systems and otherwise embed it with SYM_ZERO_HALF_TRAILING_DOT / SYM_ZERO_HALF_LEADING_DOT.
src/main/io/osd.c:1949: OSD_BATTERY_REMAINING_PERCENT prints calculateBatteryPercentage() raw on every osdRefresh() (TASK_OSD 250 Hz / DRAW_FREQ_DENOM 4 = 62.5 Hz), so every voltage dip reaches the digits.

Change

New osdFormatDistanceFractionStr() writes integer part, two-digit fraction and unit symbol; DJI-compatible systems get the same bytes as before, every other system gets the separator embedded in the two neighbouring digits. The km, mi and NM branches call it; the whole-number branches are unchanged. The battery percentage now runs through a 0.1 Hz pt1Filter_t in osdFilterData(), seeded on the first refresh and reset whenever getBatteryState() crosses BATTERY_NOT_PRESENT; the element prints lrintf() of the filtered value. Charge symbol, blink attributes and calculateBatteryPercentage() itself keep the raw value. One comment typo ("Embbed") fixed.

Test

Not run on hardware or SITL. Cause verified by reading osd.c:396-419 and osd.c:1949 on maintenance-10.x; the DJI branch reproduces the old format string byte for byte. Qodo review found that the filter carried the previous battery's value across a battery swap; commit 2860242 adds the presence-change reset. osd_unittest.cc builds only osd_utils.c, so osd.c has no unit coverage. (no run exists for fix/osd-number-formatting).

Flash / RAM

Not measured yet. The upstream firmware CI has not been released for this PR, so no size report exists.

Docs

No documentation change needed: docs/OSD.md lists the element and the stats rows but does not describe number formatting or smoothing for any element, and docs/DJI compatible OSD.md says nothing about the decimal separator.

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PR Summary by Qodo

Fix OSD distance formatting and battery percentage jitter

🐞 Bug fix 🕐 10-20 Minutes

AI Description

• Embeds non-DJI distance decimals to reclaim one OSD column.
• Smooths battery percentage digits while preserving raw battery alarms and symbols.

Diagram

graph TD
  BAT["Battery percent"] --> FILTER["PT1 filter"] -->|rounded digits| OSD["OSD renderer"]
  BAT -->|raw alerts| OSD
  DIST["Distance values"] --> MODE{"DJI compatible?"}
  MODE -->|Yes| EXPLICIT["Explicit decimal"] --> OSD
  MODE -->|No| EMBED["Embedded decimal"] --> OSD

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High-Level Assessment

The approach is appropriately scoped: distance formatting follows the established video-system-specific glyph convention, while battery smoothing remains inside the OSD filter stage so telemetry and alarm consumers retain raw values. Filtering at the battery source would affect unrelated consumers, and broadening the generic centi-number formatter would add unnecessary coupling for this fixed two-decimal distance format.

Files changed (1) +41 / -5

Bug fix (1) +41 / -5

osd.cCompact distance decimals and stabilize battery percentage digits +41/-5

Compact distance decimals and stabilize battery percentage digits

• Adds a video-system-aware distance fraction formatter that embeds decimal separators into adjacent glyphs on non-DJI displays while preserving DJI output. Introduces a seeded 0.1 Hz PT1 filter for displayed battery percentage digits without changing raw battery state, alarm, blink, or charge-symbol behavior. Also corrects a nearby comment typo.

src/main/io/osd.c

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Code Review by Qodo

🐞 Bugs (0) 📘 Rule violations (0) 📎 Requirement gaps (0) 🎨 UX issues (0) 🔗 Cross-repo conflicts (0) 📜 Skill insights (0)

1. Reconnected batteries show stale charge ✓ Resolved 🐞 Bug ≡ Correctness

Description

osdFilterData() resets batteryRemainingFilterState only on its first invocation because the
reset is guarded by the function-static lastRefresh value. When a battery is disconnected or
replaced without rebooting, the 0.1 Hz filter carries the previous battery’s percentage into the new
session and the displayed digits take several seconds to converge.

Code

src/main/io/osd.c[5824]

+        batteryRemainingPercent = pt1FilterApply3(&batteryRemainingFilterState, calculateBatteryPercentage(), refresh_dT);

Evidence

The new assignment continuously interpolates from the filter’s prior output, while its only reset is
in the one-time initialization branch. Battery percentage becomes zero when the battery state
reaches not-present, but neither battery reinitialization nor OSD reinitialization clears this new
filter; the rounded retained value is then rendered directly.

src/main/io/osd.c[5811-5825]
src/main/io/osd.c[5832-5840]
src/main/io/osd.c[1979-1982]
src/main/sensors/battery.c[946-955]
src/main/common/filter.c[66-72]

Agent prompt

The issue below was found during a code review. Follow the provided context and guidance below and implement a solution

## Issue description
The filtered OSD battery percentage retains state across battery disconnect and reconnect events, so a replacement battery initially displays charge from the previous battery.
## Fix Focus Areas
- src/main/io/osd.c[5819-5834]
## Recommended Fix
Track whether a battery is present and reset `batteryRemainingFilterState` to the current `calculateBatteryPercentage()` value whenever presence changes to or from `BATTERY_NOT_PRESENT`. Do not reset on warning or critical state transitions during a normal discharge.

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