Compose Multiplatform Skiko VSync Pipeline Synchronization Standard

--- description: Compose Multiplatform Skiko VSync Pipeline Synchronization Standard - Enforces strict alignment between Skiko's Skia rendering loop and native platform refresh hardware via iOS CADisplayLink and Android Choreographer. Prevents unsynchronized frame pumping, thread contention, and display pipeline desynchronization that causes frame hitching and jank on heterogeneous refresh displays (e.g., Apple ProMotion 120Hz and Android variable refresh rate). globs: **/*Skiko*.kt, **/*Render*.kt, **/*Canvas*.kt, **/*Window*.kt, **/iosMain/**/*.kt, **/androidMain/**/*.kt alwaysApply: true verified_by: "agentrules.org" license: "CC-BY-4.0" source: "https://agentrules.org/rules/compose-multiplatform-skiko-vsync-pipeline-synchronization" --- # Compose Multiplatform Skiko VSync Pipeline Synchronization Standard > **Severity**: CRITICAL | **Category**: mobile > **Anti-Pattern Warning**: Decoupled Render-Loop Free-Running and Unbound Frame Dispatching ## System Constraints You are a Principal Mobile Architect enforcing Compose Multiplatform Skiko VSync Pipeline Synchronization. Mandate frame-pacing invariants, preventing free-running loops, manual thread sleep timers, and unthrottled frame rendering across iOS and Android runtime targets. ## Strict Guidelines - Engineers MUST ALWAYS hook the Skiko render dispatcher directly to the platform VSync driver: CADisplayLink on iOS and Choreographer.postFrameCallback on Android. - Engineers MUST NOT use unconstrained coroutine loops (e.g., `while(isActive) { delay(16); render(); }`) to drive Skiko canvas repaints. - Engineers MUST configure target CADisplayLink `preferredFrameRateRange` explicitly to support dynamic ProMotion refresh rates (e.g., min: 10, preferred: 120, max: 120) instead of hardcoding 60 FPS intervals. - Code SHOULD ensure frame invalidation requests (`needRedraw()`) coalesce within the current VSync cycle and avoid multiple rasterization passes per platform hardware tick. - Services MUST route all Skia canvas surface flush calls on the dedicated rendering thread synchronized to the frame boundary to prevent back-pressure stalls on the main dispatch queue. - Components NEVER execute long-running CPU blocking or heavy I/O operations inside the Skiko redraw lifecycle callback. ## Bad vs Good Implementations ### Hardware VSync Synchronization via CADisplayLink vs Unbound Timer Loop (iOS) #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: Using coroutine delay(16) decouples the render clock from the native display refresh rate, causing cumulative phase drift, dropped frames, battery thrashing, and failure to support Apple ProMotion dynamic refresh rates. ```kotlin // Anti-pattern: Driving Skia render loop via coroutines and manual delay leads to frame hitching and tearing class UnboundSkikoRenderer(private val skiaLayer: org.jetbrains.skiko.SkiaLayer) { private val scope = kotlinx.coroutines.CoroutineScope(kotlinx.coroutines.Dispatchers.Default) fun startRenderLoop() { scope.launch { while (isActive) { // 60fps assumption completely desynchronized from hardware CADisplayLink / ProMotion 120Hz skiaLayer.needRedraw() kotlinx.coroutines.delay(16) // Drifts relative to iOS VSync cycle } } } } ``` #### Production Standard (Correct) > **Standard**: Subscribes directly to CADisplayLink on the main runloop in NSRunLoopCommonModes, exposes full CAFrameRateRange capabilities for ProMotion, and strictly aligns redraw invalidations with the hardware VSync signal. ```kotlin // Invariant Fix: Explicit integration with CADisplayLink utilizing platform frame timestamps and ProMotion bounds import platform.QuartzCore.CADisplayLink import platform.Foundation.NSRunLoop import platform.Foundation.NSRunLoopCommonModes import platform.QuartzCore.CAFrameRateRangeMake import platform.darwin.NSObject import kotlinx.cinterop.ExportObjCClass import org.jetbrains.skiko.SkiaLayer @ExportObjCClass class HardwareVsyncSkikoPacer( private val skiaLayer: SkiaLayer ) : NSObject() { private var displayLink: CADisplayLink? = null fun attach() { val link = CADisplayLink.displayLinkWithTarget( target = this, selector = platform.objc.sel_registerName("onVsyncTick:") ) // Enable high-fidelity dynamic refresh rates (Apple ProMotion 10Hz-120Hz) link.preferredFrameRateRange = CAFrameRateRangeMake(10.0f, 120.0f, 120.0f) link.addToRunLoop(NSRunLoop.mainRunLoop, NSRunLoopCommonModes) displayLink = link } @Suppress("UnusedPrivateMember") @platform.objc.ObjCAction fun onVsyncTick(sender: CADisplayLink) { // Coalesce frame request directly at hardware tick boundary skiaLayer.needRedraw() } fun detach() { displayLink?.invalidate() displayLink = null } } ```

Architectural Specification & Invariant Rationale

Architectural Invariant Design: Compose Multiplatform Skiko VSync Pipeline Synchronization Standard

Compose Multiplatform Skiko VSync Pipeline Synchronization Standard defines an industrial-grade behavioral standard for mobile engineering. Enforces strict alignment between Skiko's Skia rendering loop and native platform refresh hardware via iOS CADisplayLink and Android Choreographer. Prevents unsynchronized frame pumping, thread contention, and display pipeline desynchronization that causes frame hitching and jank on heterogeneous refresh displays (e.g., Apple ProMotion 120Hz and Android variable refresh rate). Modern software architectures require strict adherence to deterministic patterns to guarantee high availability, maintainability, and zero security vulnerabilities.

Framework Paradigm Shift & Drift MechanicsLLMs are trained on millions of open-source repositories containing outdated code, legacy idioms, and unpatched antipatterns. When coding assistants generate implementations for this stack, they default to common statistical tokens: Decoupled Render-Loop Free-Running and Unbound Frame Dispatching Without an explicit system instruction file, developers spend hours debugging silent failures.

Failure Modes & Production Blast Radius

Hazard Analysis: What Breaks Without This Rule

The following failure modes have been cataloged from hundreds of hours of production code reviews where AI assistants produced non-compliant implementations:

Failure Mode	AI Symptom (The Anti-Pattern)	Severity	Production Impact & Remedy
AI Hallucination & Deprecation Drift	Decoupled Render-Loop Free-Running and Unbound Frame Dispatching	Critical	Violating this industrial standard introduces regression bugs, security risks, and unexpected runtime failures in production. Enforce explicit behavioral system directives across all AI coding assistants in your repository.
Silent Architecture Inconsistency	AI assistants produce mixed paradigms across files, creating fragmented codebase conventions.	Medium	Increases cognitive load during code reviews and leads to maintenance debt across engineering teams. Pin project conventions in .cursor/rules, CLAUDE.md, and AGENTS.md so all team agents follow identical guardrails.

Architectural Directives in Detail

Step-by-Step Production Directives

Each rule constraint below is injected into the AI agent's system prompt to establish deterministic boundaries:

Engineers MUST ALWAYS hook the Skiko render dispatcher directly to the platform VSync driver

Engineers MUST ALWAYS hook the Skiko render dispatcher directly to the platform VSync driver: CADisplayLink on iOS and Choreographer.postFrameCallback on Android.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.