Fix pan & swipe update event values on Windows by jeremy-visionaid · Pull Request #33540 · dotnet/maui

jeremy-visionaid · 2026-01-14T20:40:23Z

Description of Change

Using the delta from ManipulationDeltaRoutedEventArgs for cumulative displacement generates invalid event data. Consider the following sequence for X coordinates moving the mouse from left to right:

x = 0; delta = 0; => totalX = 0;
x = 10; delta = 10; => totalX = 20;
x = 11; delta = 1; => totalX = 12;

On low end hardware or complex scenes, this causes the pan to jump around when dragging.

Issues Fixed

Fixes: #33539

Using the delta from ManipulationDeltaRoutedEventArgs for cumulative displacement generates invalid event data. Consider the following sequence for X coordinates moving the mouse from left to right: x = 0; delta = 0; => totalX = 0; x = 10; delta = 10; => totalX = 20; x = 11 delta = 1; => totalX = 12; On low end hardware or complex scenes, this causes the pan to jump around when dragging. Fixes: dotnet#33539

dotnet-policy-service · 2026-01-14T20:40:39Z

Hey there @@jeremy-visionaid! Thank you so much for your PR! Someone from the team will get assigned to your PR shortly and we'll get it reviewed.

jeremy-visionaid · 2026-01-14T20:44:09Z

@PureWeen Looks like you wrote this part of the gesture manager. Any idea why it's using the manipulation delta? I assume there was some reason for it, but the values it generates can lead to wildly incorrect values for the pan & swipe events.

MauiBot · 2026-03-22T13:37:49Z

🤖 AI Summary

📊 Expand Full Review — ab0ceb8 · Fix pan & swipe update event values on Windows

🔍 Pre-Flight — Context & Validation

Issue: #33539 - Pan gesture update events have incorrect values on Windows
PR: #33540 - Fix pan & swipe update event values on Windows
Platforms Affected: Windows only (issue), user-requested testing platform: android
Files Changed: 1 implementation, 0 test

Key Findings

The linked issue is verified on Windows and describes non-monotonic pan update values that make dragged elements jump backwards.
The PR changes only src/Controls/src/Core/Platform/GestureManager/GesturePlatformManager.Windows.cs, replacing delta + cumulative with cumulative values for both swipe and pan update callbacks.
No test files were included in the PR, and no prior agent review was found in PR discussion.
The requested test platform (android) does not match the affected platform (Windows), so Gate verification cannot meaningfully validate the bug on this host.

Edge Cases From Discussion

The same erroneous accumulation pattern affects both PanGestureRecognizer and SwipeGestureRecognizer update values.
The PR author notes the bug becomes more visible on low-end hardware or complex scenes where manipulation deltas fluctuate.

Fix Candidates

#	Source	Approach	Test Result	Files Changed	Notes
PR	PR #33540	Stop adding `e.Delta.Translation` to `e.Cumulative.Translation` and forward only cumulative translation values for Windows pan/swipe update callbacks.	⏳ PENDING (Gate)	`src/Controls/src/Core/Platform/GestureManager/GesturePlatformManager.Windows.cs`	Original PR

🚦 Gate — Test Verification

Gate Result: ⚠️ SKIPPED

Platform: android
Mode: Full Verification

Tests FAIL without fix: ❌
Tests PASS with fix: ❌

Notes

PR Fix pan & swipe update event values on Windows #33540 contains no test files.
The linked issue Pan gesture update events have incorrect values on Windows #33539 is Windows-only, while the requested test platform is android.
The changed file, src/Controls/src/Core/Platform/GestureManager/GesturePlatformManager.Windows.cs, is never exercised on android, so fail/pass verification on android would be meaningless.
A meaningful Gate for this PR would require Windows-based validation.

🔧 Fix — Analysis & Comparison

Fix Candidates

#	Source	Approach	Test Result	Files Changed	Notes
1	try-fix (`claude-opus-4.6`)	Accumulate `e.Delta.Translation` in dedicated running fields reset at gesture start, then send the tracked totals.	⚠️ Blocked	1 file	Alternative to `cumulative only`; blocked because Windows validation is unavailable on Linux.
2	try-fix (`claude-sonnet-4.6`)	Compute translation from `e.Position - startPosition` instead of any translation properties.	⚠️ Blocked	1 file	Geometric alternative using start position; also blocked by missing Windows validation.
3	try-fix (`gpt-5.3-codex`)	Restrict the cumulative-translation change to running updates only instead of all statuses.	⚠️ Blocked	1 file	Narrower variant; still unvalidated and less convincing than the PR fix.
4	try-fix (`gemini-3-pro-preview`)	Compute translation in global coordinate space from a captured start point.	⚠️ Blocked	1 file	Stable-frame geometric variant; also unvalidated on this host.
5	try-fix (`gemini-3-pro-preview`, cross-pollination)	Set the manipulation container/reference frame to the window root so cumulative translation is measured in a stable coordinate space.	⚠️ Blocked	1 file	Interesting WinUI-specific idea, but broader/riskier and still unvalidated on Linux.
6	try-fix (`claude-opus-4.6`, cross-pollination)	Capture the initial cumulative translation as a baseline and subtract it from subsequent cumulative values.	⚠️ Blocked	1 file	More defensive variant; mostly equivalent to the PR fix in normal WinUI behavior, but more complex.
7	try-fix (`claude-sonnet-4.6`, cross-pollination)	Derive translation directly from pointer position minus the gesture start position.	⚠️ Blocked	1 file	Avoids translation APIs entirely, but still needs Windows validation.
8	try-fix (`gemini-3-pro-preview`, cross-pollination)	Track raw active-pointer centroid positions and accumulate translation manually.	⚠️ Blocked	1 file	Most invasive approach; far riskier than the PR fix and still unvalidated.
PR	PR #33540	Send only `e.Cumulative.Translation` for Windows pan/swipe updates.	⚠️ Unverifiable on this host	1 file	Original PR fix; simplest and most directly aligned with the reported arithmetic bug.

Cross-Pollination

Model	Round	New Ideas?	Details
claude-opus-4.6	1	Yes	Delta-only accumulation fields instead of using `e.Cumulative`.
claude-sonnet-4.6	1	Yes	Derive translation from current pointer position minus gesture start position.
gpt-5.3-codex	1	Yes	Limit the fix to running gesture updates rather than all states.
gemini-3-pro-preview	1	Yes	Derive translation from a stable global coordinate frame.
claude-opus-4.6	2	No	NO NEW IDEAS
claude-sonnet-4.6	2	No	NO NEW IDEAS
gpt-5.3-codex	2	No	NO NEW IDEAS
gemini-3-pro-preview	2	Yes	Set manipulation container/root to stabilize WinUI cumulative translation.
claude-opus-4.6	3	Yes	Subtract an initial cumulative baseline from later cumulative values.
claude-sonnet-4.6	3	Yes	Use pointer-position deltas instead of manipulation translation.
gpt-5.3-codex	3	No	NO NEW IDEAS
gemini-3-pro-preview	3	Yes	Use raw pointer centroid positions instead of manipulation translation.

Exhausted: Yes (3 rounds completed; no validated alternative beat the PR fix)
Selected Fix: PR — best current candidate because it directly removes the double-counting arithmetic with the smallest, clearest change. Full validation still requires Windows.

📋 Report — Final Recommendation

⚠️ Final Recommendation: REQUEST CHANGES

Phase Status

Phase	Status	Notes
Pre-Flight	✅ COMPLETE	Windows-only gesture bug, 1 implementation file changed, no tests added.
Gate	⚠️ SKIPPED	Requested platform was android, but the bug and fix are Windows-only, so meaningful fail/pass verification was not possible.
Try-Fix	✅ COMPLETE	8 attempts, 0 passing, all blocked by lack of Windows runtime/SDK on Linux host.
Report	✅ COMPLETE

Summary

The PR fix is plausible and is the simplest candidate explored: it removes the obvious double-counting bug by forwarding only e.Cumulative.Translation for Windows pan and swipe updates. However, this review could not validate the fix empirically because the requested test platform (android) does not exercise the changed Windows code, the PR adds no tests, and the current host cannot run Windows validation.

Root Cause

GesturePlatformManager.Windows.cs was combining e.Delta.Translation with e.Cumulative.Translation for pan and swipe updates. Because the cumulative value already includes the current delta, this double-counts movement and can make the reported gesture coordinates jump backward or overshoot.

Fix Quality

The PR change is the best option among the explored candidates from a code-quality standpoint: it is the smallest and most direct correction to the arithmetic bug, while the alternatives were either more complex, more invasive, or both. Still, without a Windows Gate run or test coverage that reproduces the regression, the fix remains unverified. I recommend requesting changes for Windows-based verification and/or regression coverage before merge.

kubaflo · 2026-03-22T23:51:53Z

Code Review — PR #33540

✅ Verdict: APPROVE

This is a clean, correct 2-line fix for a real arithmetic bug.

Root Cause Analysis

The original code computed displacement as:

e.Delta.Translation.X + e.Cumulative.Translation.X

Per the WinUI docs:

Cumulative = overall changes since the beginning of the manipulation (total displacement)
Delta = most recent changes of the current manipulation (per-event increment)

Since Cumulative already includes the current Delta, adding them together double-counts movement. The PR description example illustrates this perfectly:

x = 0;  delta = 0;  => totalX = 0;   (correct)
x = 10; delta = 10; => totalX = 20;  (should be 10 - overshot)
x = 11; delta = 1;  => totalX = 12;  (should be 11 - jumped backward from 20)

Cross-Platform Consistency Check

The IPanGestureController.SendPan(totalX, totalY, ...) and ISwipeGestureController.SendSwipe(totalX, totalY) parameters are documented as cumulative total displacement. I verified all platforms:

Platform	Source of displacement	Correct?
iOS	`r.TranslationInView()` — cumulative from gesture start	✅
Android	Cumulative `x, y` params passed to `OnPan()`/`OnSwipe()`	✅
Windows (before fix)	`e.Delta + e.Cumulative` — double-counted	❌
Windows (after fix)	`e.Cumulative.Translation` only	✅

The fix brings Windows in line with how iOS and Android already work.

What Changed

Both HandleSwipe and HandlePan in GesturePlatformManager.Windows.cs now pass only e.Cumulative.Translation.{X,Y} instead of e.Delta.Translation.{X,Y} + e.Cumulative.Translation.{X,Y}.

Potential Concern: No Tests

This PR does not add tests, which is understandable — testing this requires mocking ManipulationDeltaRoutedEventArgs (a WinUI sealed type) or running on Windows with actual gesture input. The fix is straightforward enough that the risk of regression is low, but a device test or manual validation on Windows would be ideal before merge.

Summary

Minimal, surgical, correct. The math was wrong, now it is right, and it matches the other platforms. 👍

…indows

### Description of Change Using the delta from ManipulationDeltaRoutedEventArgs for cumulative displacement generates invalid event data. Consider the following sequence for X coordinates moving the mouse from left to right: x = 0; delta = 0; => totalX = 0; x = 10; delta = 10; => totalX = 20; x = 11; delta = 1; => totalX = 12; On low end hardware or complex scenes, this causes the pan to jump around when dragging. ### Issues Fixed Fixes: #33539 Co-authored-by: Jakub Florkowski <42434498+kubaflo@users.noreply.github.com>

### Description of Change Using the delta from ManipulationDeltaRoutedEventArgs for cumulative displacement generates invalid event data. Consider the following sequence for X coordinates moving the mouse from left to right: x = 0; delta = 0; => totalX = 0; x = 10; delta = 10; => totalX = 20; x = 11; delta = 1; => totalX = 12; On low end hardware or complex scenes, this causes the pan to jump around when dragging. ### Issues Fixed Fixes: dotnet#33539 Co-authored-by: Jakub Florkowski <42434498+kubaflo@users.noreply.github.com>

### Description of Change Using the delta from ManipulationDeltaRoutedEventArgs for cumulative displacement generates invalid event data. Consider the following sequence for X coordinates moving the mouse from left to right: x = 0; delta = 0; => totalX = 0; x = 10; delta = 10; => totalX = 20; x = 11; delta = 1; => totalX = 12; On low end hardware or complex scenes, this causes the pan to jump around when dragging. ### Issues Fixed Fixes: #33539 Co-authored-by: Jakub Florkowski <42434498+kubaflo@users.noreply.github.com>

dotnet-policy-service bot added the community ✨ Community Contribution label Jan 14, 2026

build-analysis bot mentioned this pull request Jan 15, 2026

"We stopped hearing from agent Azure Pipelines 32. Verify the agent machine is running and has a healthy network connection" dotnet/dnceng#1886

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MauiBot added s/agent-changes-requested AI agent recommends changes - found a better alternative or issues s/agent-fix-pr-picked AI could not beat the PR fix - PR is the best among all candidates s/agent-reviewed PR was reviewed by AI agent workflow (full 4-phase review) labels Mar 22, 2026

kubaflo changed the base branch from main to inflight/current March 22, 2026 23:53

Merge branch 'inflight/current' into fix-pan-swipe-update-values-on-w…

42fa6db

…indows

kubaflo approved these changes Mar 22, 2026

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kubaflo merged commit 3c527b7 into dotnet:inflight/current Mar 22, 2026
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This was referenced Mar 23, 2026

The Operation will be canceled. The next steps may not contain expected logs. dotnet/dnceng#3008

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[android-arm64] The Operation will be canceled. The next steps may not contain expected logs. dotnet/dnceng#6408

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PureWeen mentioned this pull request Apr 6, 2026

March 30th, Inflight Candidate #34617

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Fix pan & swipe update event values on Windows#33540

Fix pan & swipe update event values on Windows#33540
kubaflo merged 2 commits intodotnet:inflight/currentfrom
jeremy-visionaid:fix-pan-swipe-update-values-on-windows

jeremy-visionaid commented Jan 14, 2026 •

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MauiBot commented Mar 22, 2026

Key Findings

Edge Cases From Discussion

Fix Candidates

Gate Result: ⚠️ SKIPPED

Notes

Fix Candidates

Cross-Pollination

⚠️ Final Recommendation: REQUEST CHANGES

Phase Status

Summary

Root Cause

Fix Quality

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kubaflo commented Mar 22, 2026

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jeremy-visionaid commented Jan 14, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Description of Change

Issues Fixed

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jeremy-visionaid commented Jan 14, 2026

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MauiBot commented Mar 22, 2026

🤖 AI Summary

Key Findings

Edge Cases From Discussion

Fix Candidates

Gate Result: ⚠️ SKIPPED

Notes

Fix Candidates

Cross-Pollination

⚠️ Final Recommendation: REQUEST CHANGES

Phase Status

Summary

Root Cause

Fix Quality

Uh oh!

kubaflo commented Mar 22, 2026

Code Review — PR #33540

✅ Verdict: APPROVE

Root Cause Analysis

Cross-Platform Consistency Check

What Changed

Potential Concern: No Tests

Summary

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jeremy-visionaid commented Jan 14, 2026 •

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