chore: Trim comments on the platform transition path

[MatiPl01]

Drops comments that restate the code and shortens those carrying a second sentence the first already implied.

The Kotlin binary search in CSSEasing is renamed from lastIndexAtOrBefore to firstSmallerOrEqual, matching its C++ counterpart in CSS/utils/algorithms.cpp, so both turn up in one grep. That is what the comment pointing across languages was there for. They cannot share a file - ObjectAnimator calls TimeInterpolator.getInterpolation from Java every frame, so the curve has to be evaluated Java-side rather than over JNI.

Kept the notes that would otherwise be re-derived: the easing type mirroring PlatformEasing::Type, resolveView throwing rather than returning null, and overrideDurationScale being @hide.

[coderabbitai]

📝 Walkthrough

Summary by CodeRabbit

• Documentation
  • Clarified CSS easing behavior and handling of duplicate stops without changing interpolation results.
  • Added guidance on animation playback acceptance, retrying pending starts, interrupted transitions, and resolving absolute timelines.
  • Updated duration-scaling guidance to explain how animation durations are adjusted during playback.

Walkthrough

The PR updates CSS easing, transition playback, and duration-scaling documentation. It also renames a private easing lookup helper. Runtime behavior and public declarations remain unchanged.

Changes

CSS animation updates

Layer / File(s)	Summary
CSS easing helper update packages/react-native-reanimated/android/src/main/java/com/swmansion/reanimated/css/CSSEasing.kt	The duplicate-x lookup helper is renamed to firstSmallerOrEqual. Both interpolators use the new name.
Transition and duration documentation packages/react-native-reanimated/android/src/main/java/com/swmansion/reanimated/css/CSSPlatformTransitionsManager.kt, packages/react-native-reanimated/android/src/main/java/com/swmansion/reanimated/css/DurationScale.kt	Comments clarify native playback acceptance, pending-start retries, interruption handling, elapsed-time resolution, and duration scaling.

Estimated code review effort: 1 (Trivial) | ~3 minutes

Possibly related PRs

• software-mansion/react-native-reanimated#10090: Updates the same CSS easing, transition, and duration-scaling code.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the primary change: trimming comments on the platform transition path.
Description check	✅ Passed	The description accurately explains the comment cleanup, helper rename, retained notes, and Java-side easing evaluation.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch @matipl01/android-css-trim-transition-comments

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In
`@packages/react-native-reanimated/android/src/main/java/com/swmansion/reanimated/css/CSSEasing.kt`:
- Line 26: Rename the Kotlin helper firstSmallerOrEqual and its corresponding
C++ helper to lastIndexAtOrBefore, updating all declarations and call sites
while preserving the existing returned-index behavior.

🪄 Autofix

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: ASSERTIVE

Plan: Pro Plus

Run ID: ee65557b-4a73-4e92-a702-bbefc65df96a

📥 Commits

Reviewing files that changed from the base of the PR and between dd83fb4 and 98b66be.

📒 Files selected for processing (1)

• packages/react-native-reanimated/android/src/main/java/com/swmansion/reanimated/css/CSSEasing.kt

[coderabbitai]

📐 Maintainability & Code Quality | 🔵 Trivial | ⚡ Quick win

🧩 Analysis chain

🏁 Script executed:

#!/bin/bash
set -euo pipefail

fd -i '^algorithms\.cpp$' packages/react-native-reanimated -x \
  rg -n -C 12 '\b(firstSmallerOrEqual|lastIndexAtOrBefore)\b' {}

Repository: software-mansion/react-native-reanimated

Length of output: 534

---

🏁 Script executed:

#!/bin/bash
set -euo pipefail

printf '%s\n' '--- Kotlin helper and call sites ---'
rg -n -C 14 '\b(firstSmallerOrEqual|lastIndexAtOrBefore)\b' \
  packages/react-native-reanimated/android/src/main/java/com/swmansion/reanimated/css/CSSEasing.kt

printf '%s\n' '--- C++ declaration and related references ---'
rg -n -C 8 '\bfirstSmallerOrEqual\b|\blastIndexAtOrBefore\b' \
  packages/react-native-reanimated/common/cpp \
  packages/react-native-reanimated/android \
  packages/react-native-reanimated/ios 2>/dev/null || true

printf '%s\n' '--- Documentation describing the helper ---'
rg -n -i -C 5 'smaller|upper.?bound|binary search|easing' \
  packages/react-native-reanimated/common/cpp \
  packages/react-native-reanimated/android/src/main/java/com/swmansion/reanimated/css \
  2>/dev/null | head -240

Repository: software-mansion/react-native-reanimated

Length of output: 21098

---

🏁 Script executed:

#!/bin/bash
set -euo pipefail

printf '%s\n' '--- all matching declarations and uses ---'
rg -n -C 6 '\bfirstSmallerOrEqual\b|\blastIndexAtOrBefore\b' packages/react-native-reanimated || true

printf '%s\n' '--- algorithm files ---'
fd -i 'algorithms\.(h|cpp)$' packages/react-native-reanimated -x sh -c '
  echo "### $1"
  cat -n "$1"
' sh {}

printf '%s\n' '--- point-array construction and interpolation inputs ---'
rg -n -C 8 'pointsX|easingPointsX|LinearStopsInterpolator|StepsInterpolator|linear\(' \
  packages/react-native-reanimated/common \
  packages/react-native-reanimated/android/src/main/java \
  2>/dev/null | head -300

Repository: software-mansion/react-native-reanimated

Length of output: 23814

---

🏁 Script executed:

python3 - <<'PY'
from bisect import bisect_right

def kotlin_equivalent(x, points):
    low, high = 0, len(points)
    while low < high:
        mid = (low + high) >> 1
        if points[mid] <= x:
            low = mid + 1
        else:
            high = mid
    return 0 if low == 0 else low - 1

cases = [
    ([-1.0, 0.0, 0.5, 1.0], -2.0),
    ([-1.0, 0.0, 0.5, 1.0], -1.0),
    ([-1.0, 0.0, 0.5, 1.0], 0.5),
    ([-1.0, 0.0, 0.5, 1.0], 2.0),
    ([0.0, 0.5, 0.5, 1.0], 0.5),
]

for points, x in cases:
    actual = kotlin_equivalent(x, points)
    expected_upper_bound = bisect_right(points, x) - 1
    expected_with_fallback = max(0, expected_upper_bound)
    print({
        "points": points,
        "x": x,
        "returned": actual,
        "last_index_at_or_before": expected_upper_bound,
        "implementation_with_below-first-fallback": expected_with_fallback,
    })
    assert actual == expected_with_fallback
PY

Repository: software-mansion/react-native-reanimated

Length of output: 860

---

Rename the helper to match its returned index.

For x >= pointsX[0], firstSmallerOrEqual returns the last index at or before x, including the last duplicate. Rename the Kotlin and C++ helpers to lastIndexAtOrBefore.

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In
`@packages/react-native-reanimated/android/src/main/java/com/swmansion/reanimated/css/CSSEasing.kt`
at line 26, Rename the Kotlin helper firstSmallerOrEqual and its corresponding
C++ helper to lastIndexAtOrBefore, updating all declarations and call sites
while preserving the existing returned-index behavior.

[MatiPl01]

Folded into the PRs that introduce these comments (#10090 and #10214), so this carries no changes of its own.