MotionEyes Animation Debug

Overview

Use MotionEyes as temporary observability for SwiftUI animation debugging. Instrument targeted values and geometry, capture time-series logs, compare observed motion against expected motion, apply fixes, re-validate, and clean up all agent-added tracing.

Workflow

Follow this exact order:

1. Confirm the complaint and expected behavior in measurable terms.
2. Locate the target view and the state values that drive the animation.
3. Ensure MotionEyes availability; if missing, auto-integrate the MotionEyes package into the app target before continuing.
4. Add temporary .motionTrace(...) instrumentation with Trace.value, Trace.geometry, and (for scroll issues) Trace.scrollGeometry metrics named after user intent.
5. Run the app and reproduce the issue.
6. Capture logs with XcodeBuildMCP first; fallback to CLI log streaming if MCP is unavailable.
7. Analyze how values evolve over time versus expected behavior.
8. Implement a fix, rerun, and verify the motion now matches intent.
9. Remove only agent-added MotionEyes imports/modifiers/trace metrics from this run; never remove user-authored pre-existing MotionEyes code.

Instrumentation Rules

Add instrumentation only to the minimum set of views needed to test the complaint.

• Use stable, semantic trace names that match the user complaint.
• Set the values to the same name as the property, so it's easier to identify.
• Use geometry tracing when motion is relative to container or sibling layout, or when checking true on-screen presentation movement.
• Use scroll geometry tracing when the bug involves ScrollView offset, visible region, content size, insets, or restoration behavior.
• Place Trace.scrollGeometry on the ScrollView container (or an immediate descendant bound to the same scroll context), not on unrelated overlays.

Choose geometry mode based on intent:

• Layout relationship in SwiftUI coordinates: space: .swiftUI(.global), source: .layout
• Window-relative layout motion: space: .window, source: .layout
• Physical screen-visible motion (including presentation wiggle): space: .screen, source: .presentation

Example template:

import MotionEyes
import SwiftUI

struct CardMotionExample: View {
    @State private var opacity = 1.0
    @State private var offset = CGSize.zero

    var body: some View {
        RoundedRectangle(cornerRadius: 16)
            .fill(.orange)
            .frame(width: 180, height: 120)
            .opacity(opacity)
            .offset(offset)
            .motionTrace("Card Motion", fps: 30) {
                Trace.value("opacity", opacity)
                Trace.value("offset", CGPoint(x: offset.width, y: offset.height))
                Trace.geometry(
                    "cardFrame",
                    properties: [.minX, .minY, .width, .height],
                    space: .swiftUI(.global),
                    source: .layout
                )
            }
            .onTapGesture {
                withAnimation(.easeInOut(duration: 0.6)) {
                    opacity = opacity == 1 ? 0.4 : 1
                    offset = offset == .zero ? CGSize(width: 0, height: 36) : .zero
                }
            }
    }
}

Scroll-focused template:

ScrollView {
    content
}
.motionTrace("Chat Scroll", fps: 30) {
    Trace.scrollGeometry(
        "scrollMetrics",
        properties: [.contentOffsetY, .visibleRectMinY, .visibleRectHeight]
    )
}

Log Capture

Prefer XcodeBuildMCP:

1. Call mcp__XcodeBuildMCP__session_show_defaults.
2. Set missing defaults with mcp__XcodeBuildMCP__session_set_defaults.
3. Build and run with mcp__XcodeBuildMCP__build_run_sim if needed.
4. Start capture with mcp__XcodeBuildMCP__start_sim_log_cap:
   • captureConsole: true
   • subsystemFilter: "MotionEyes" (or broader "all" when needed)
5. Reproduce the animation.
6. Stop capture with mcp__XcodeBuildMCP__stop_sim_log_cap and inspect returned logs.

Fallback CLI if MCP is unavailable:

xcrun simctl spawn booted log stream \
  --style compact \
  --level debug \
  --predicate 'subsystem == "MotionEyes"'

MotionEyes Log Analysis

Use these signatures:

• Value samples: [MotionEyes][View][Metric] key=value ...
• Change burst start: [MotionEyes][View][Metric] -- Start timestamp --
• Change burst end: [MotionEyes][View][Metric] -- End timestamp --

Analyze:

• Direction: sign and trend of sampled values.
• Timing: time delta from intent trigger to first Start and to End.
• Shape: monotonic change, overshoot, reversals, oscillation, flat segments.
• Relationship: compare two traces over the same time window when behavior is relative.

Do not force fixed thresholds globally; evaluate against the user’s stated expectation.

Cleanup Rules

At the end of every run:

• Remove all MotionEyes instrumentation introduced by the agent during this debugging run.
• Keep all MotionEyes instrumentation that already existed before the run.
• Remove agent-added import MotionEyes only if it was added solely for temporary tracing and is no longer needed.
• Confirm code compiles after cleanup.

Scenarios to Support

• Fade timing bug: trace opacity and verify fade begins/ends when expected.
• Wrong direction bug: trace Y-related value and confirm sign/trend match expected motion.
• Relative motion bug: trace two objects and verify their positional relationship over time.
• Scroll jump/restoration bug: trace Trace.scrollGeometry on the ScrollView and verify contentOffset/visibleRect progression through navigation and return paths.
• No motion desired: if something is meant to remain static during transition.
• Existing instrumentation safety: preserve user-authored MotionEyes traces.
• MCP unavailable: use CLI log stream and continue analysis.
• Missing package: auto-integrate MotionEyes, then execute normal workflow.

Reference

Load references/motioneyes-observability-patterns.md when choosing metrics or interpreting trace behavior.