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Rendering pipeline

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Rendering Pipeline Deep Dive

Overview

Android frame rendering follows a measure-layout-draw pipeline coordinated with display vsync. Missing frame deadlines causes jank.

Frame Pipeline

  1. Measure: determine view sizes.
  2. Layout: place views in parent bounds.
  3. Draw: record drawing commands.
  4. RenderThread/GPU: rasterize and compose.
  5. Display: present frame on next vsync.

Frame Budget

  • 60 Hz -> 16.67 ms per frame.
  • 120 Hz -> 8.33 ms per frame.
  • Exceeding budget drops/skips frames.

Common Jank Sources

  • Heavy work on main thread during input/animation.
  • Excessive layout passes (requestLayout storms).
  • Overdraw and complex alpha blending.
  • Expensive bitmap decode/transform at draw time.

Optimization Strategies

  • Flatten view hierarchies.
  • Avoid invalidating large areas unnecessarily.
  • Precompute text/layout data.
  • Move expensive work off main thread.
  • Use profiler tools to target hotspots.

Interview Traps

  • "GPU accelerated" does not mean main thread can block.
  • Smoothness requires both CPU and GPU staying within frame budget.

Key Takeaways

  • Rendering performance is deadline-driven.
  • Measure, profile, then optimize the true bottleneck.