Matěj Kašpar Jirásek

@[email protected]
159 Followers
340 Following
152 Posts
Staff iOS Engineer, currently primarily focused on performance. In my free time trying to balance on border between art and technology. 🚴 🏃 🎶 🎮
GitHubhttps://github.com/mkj-is
Websitehttps://mkj.is
Matěj Kašpar JirásekSep 10, 2025

Running my first half-marathon next month. I’m worried my four-year-old Apple Watch SE at 72% battery won’t last the entire run.

I considered the Ultra 3, but two Apple Watch SE 3s are a better deal. Their combined battery life is 2×18 = 36 hours, which is less than the 42 hours of the Ultra. The benefit is that one can stay on the charger while the other is in use. Plus, two of them are significantly cheaper than the Ultra.

The likely decision will be to run fast and save all the money. 😆

Show threadMatěj Kašpar JirásekJun 13, 2025
And what about the new Liquid Glass design? Apple provides detailed accessibility settings. If you feel these effects are too much it is quite easy to dial back them. And I am sure it will improve the perf on older devices.
Show threadMatěj Kašpar JirásekJun 13, 2025
4. Recommended values and trending insights in Xcode Organizer. For many metrics it was unclear how do we fare in comparison to other apps and what are the recommended values. https://developer.apple.com/documentation/Xcode/analyzing-the-performance-of-your-shipping-app#Compare-your-apps-metrics-with-recommended-values
Show threadMatěj Kašpar JirásekJun 13, 2025
3. Measurement of rendering performance using XCTHitchMetric in UI tests. Previously it required a custom infra to collect the data and pass it to UI test runner. This will reduce the effort needed to catch and prevent regressions. https://developer.apple.com/documentation/xctest/xcthitchmetric
Show threadMatěj Kašpar JirásekJun 13, 2025
2. Test profiling support. This gives us ability to iteratively improve heavy stack traces and test their performance in isolation.
Show threadMatěj Kašpar JirásekJun 13, 2025
1. On-the-go collection of profiling data using Power Profiler. Now anyone using the TestFlight app can help improve performance, not just devs with Instruments. Huge for debugging performance issues in the wild. https://developer.apple.com/documentation/xcode/measuring-your-app-s-power-use-with-power-profiler#Gather-power-consumption-data-on-a-device
Matěj Kašpar JirásekJan 23, 2025

Built a document-based app for previewing Lottie and DotLottie files. It features a QuickLook extension. The preview works in Xcode assets catalogues too. https://github.com/mkj-is/LottieViewerMac

It really helps to quickly debug and identify any regressions.

Matěj Kašpar JirásekSep 30, 2024
After years of working from home, I’m finally improving and organizing my office, one step at a time.
Matěj Kašpar JirásekJun 13, 2024
My crazy code once again spectacularly succeeded at crashing Swift 6 compiler. Write a code like this at your own risk.
Matěj Kašpar JirásekMay 7, 2024
Now that I have a professional conference speaker photo can I regard myself as a conference speaker?