iOS Scroll Performance

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This presentation by Kyle Sherman, LinkedIn iOS Developer for the SlideShare iOS app, goes over fixing issues with jittery scroll performance in iOS applications. The presentation goes over the basics of using Instruments to measure and fix problems, tips for using instruments, and a concrete example from the new LinkedIn iOS flagship application.

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  • I have a question about #solution1. The reason given in the slides is "circle overlap". However, drawing a mask with a circle inside also triggers offscreen rendering right? Isn't it expensive?
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iOS Scroll Performance

  1. 1. iOS Scroll Performance Kyle Sherman LinkedIn iOS Developer (SlideShare)
  2. 2. Don’t just blame a technology (i.e. Autolayout)
  3. 3. Measure!
  4. 4. Step 1: Use Instruments to measure Scroll Performance
  5. 5. Rule #1: Always profile on device!
  6. 6. Setting Up Instruments • Hit Command-I to Profile • Or Product -> Profile • Or Hold down Play button; select Profile • After done building (long time), select GPU Driver
  7. 7. Setting Up Instruments • Hit Command-I to Profile • Or Product -> Profile • Or Hold down Play button; select Profile • After done building (long time), select GPU Driver
  8. 8. Profiling • Tip #1: Decrease sample rate • Hit the Record Button • Tip #2: Set flags using Command-Down arrow • Tip #3: Double click flag to name it
  9. 9. Profiling • Tip #1: Decrease sample rate • Hit the Record Button • Tip #2: Set flags using Command-Down arrow • Tip #3: Double click flag to name it
  10. 10. Profiling • Tip #1: Decrease sample rate • Hit the Record Button • Tip #2: Set flags using Command-Down arrow • Tip #3: Double click flag to name it
  11. 11. Profiling • Tip #1: Decrease sample rate • Hit the Record Button • Tip #2: Set flags using Command-Down arrow • Tip #3: Single click flag to name it
  12. 12. Step 2: Analyze results
  13. 13. Examine Frame Rate • Examine the frame rate • Look at the CPU and GPU usage at and around large frame rate drops
  14. 14. Examine Frame Rate • If Render/Device utilization is high, requires more investigation (details later) • If not, and CPU usage is high: • Click Time Profiler so CPU usage is highlighted • Drag around peak • Look at heaviest stack trace
  15. 15. Step 3: Fix the problem
  16. 16. GPU Issues • GPU Issues require further diagnosis • Easiest way is to use Simulator • Offscreen-Rendered is worst performance hit (details to come) • Watch WWDC 2014 Session 419: Advanced Graphics and Animations for iOS Apps
  17. 17. Step 4: Measure Again!
  18. 18. Step 5: Repeat Steps 2, 3, & 4 until satisfied
  19. 19. Which brings us to our concrete example…
  20. 20. Performant Circular Images Concrete Example:
  21. 21. Applying the skills learned from the previous part, we diagnose the issue(s)
  22. 22. Problem Extremely Choppy Scrolling in this view
  23. 23. Analyzing The Data • Both the GPU utilization was high and CPU was spiking • I decided to investigate CPU usage first, because it was possibly simpler to understand • Saw suspicious methods and fixed issues in code
  24. 24. Results Frame rate increased very slightly
  25. 25. Re-measure!
  26. 26. GPU Issues • Now it was time to resolve the GPU issues • After watching WWDC 2014 Session 419, learned about rendering pipeline and how bad offscreen rendering is • The following is a screenshot with Color Offscreen-Rendered turned on
  27. 27. Color Offscreen-Rendered On
  28. 28. Analysis • Every single circle is offscreen-rendered • There are tons of circles on the screen • Need a more performant way to make the circle
  29. 29. Test Hypothesis Turn off circle creation
  30. 30. Yep! After remeasuring, scrolling is now smooth. And look at Offscreen- Rendered now!
  31. 31. Solutions
  32. 32. Solution #1 • In the WWDC session, Apple suggests creating a mask like the figure to the left of the canvas • Create the mask by drawing a circle inside of a square of the same size of the image • Only fill outside of the circle • The fill color of the mask must be the same as the view (white in this case) • Place this mask on top of the image (as a subview) Image
  33. 33. Doesn’t work in this case Reason: Circles overlap
  34. 34. Solution #2 Retrieve circular images from API
  35. 35. Valid solution, but… Adds to the number of images we serve (storage $$)
  36. 36. Solution #3 • Create a circular image mask and apply to the image • Perform on a background thread, so it doesn’t block UI thread
  37. 37. Solution #3 (code) https://gist.github.com/drumnkyle/c2ae34ea2422514c45d5
  38. 38. Solution #3 Tips • Only do it once per image if possible • You can process when image downloads or first time it is used • Add a circular version of the image to your cache
  39. 39. Resources • I highly recommend watching the WWDC video mentioned. Maybe even a few times as it goes into very good detail. • Also, when Apple TV tech talks come out, the one on performance covers these topics well as well. https://developer.apple.com/videos/play/wwdc2014-419/

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