First paint: when the user sees anything at all that’s not the browser’s default background.Its metrics have become useful for understanding loading experience, and it is now part of Google’s Web Vitals initiative. The Paint Timing API has been available in Chrome since version 60 (2017). The Paint Timing API measures the time it takes between the moment a user navigates to a URL and the moment the browser has displayed something. The Paint Timing API is a part of several performance APIs that allow web developers to observe and improve their web application performance. It’s an essential part of the toolset that lets us keep Wikimedia sites fast for everyone. Measuring web performance data in the field is critical to our monitoring. While we can measure this metric in a simulated environment, lab tests can never reproduce the real-world conditions of hundreds of millions of visitors. As different browsers behave differently, this means that a category of issues or bugs could negatively impact the initial rendering of pages on Safari specifically and we wouldn’t be able to know. However, it’s always been impossible to measure this in any form on Apple’s Safari web browser.īeing unable to measure such a basic event in the user experience for Safari visitors means that we are blind to an important category of performance issues for 20% of our visitors in the field. That particular feature has been available first as vendor-specific APIs, and now increasingly as the standardized Paint Timing API, initially on Chrome. This web browser feature tells us at what point in time content started to appear on the screen for a visitor. In this instance, we decided to commission the implementation of a feature that lets us observe web performance from an end-user perspective. Yet, all major browser engines are FLOSS projects nowadays, and sometimes browser vendors have different priorities that don’t match the needs of the Wikimedia Foundation. It might seem surprising to hear that the Wikimedia Foundation is commissioning the implementation of a web browser feature. This web browser feature tells us at what point in time content started to appear on the screen for a visitor.īy Noam Rosenthal with Gilles Dubuc, Wikimedia Performance Team Background From my understanding, with current canvas rendering this isn't an issue because the GPU textures are not being made, the frame images are stored and passed through every frame without the extra step.The story of how we decided to commission the implementation of Paint Timing API, a feature that lets us observe web performance from an end-user perspective. Videos and GIFs with more frames cause more memory pressure and at some point something is tripping because we are consuming too many resources. New GPU textures will be created on every drawImage call for every layer on every frame. From my understanding the GPU is taking over when we are drawing these images into the canvas with drawImage. Our app is decoding video (mp4) and GIFs in WebAssembly and converting them into JPEGs and PNGs (on the CPU) in workers and then rendering to canvas elements. I'm not holding you to anything but our app is crashing browser tabs because of this features just trying to establish if we should work on this which likely involves some pretty deep rewrites. We are a little unclear about "will remain that way until the final releases ship"ĭoes this mean that when it ships this setting will change or that the setting that is active in the beta usually ships to everyone. The GPU Process: Canvas Rendering feature uses new architecture to support canvas rendering that occurs in a new GPU process instead of the Web Content process. Often, but not always, entries that are enabled by default in a beta will remain that way until the final releases ship. Engineers use the mechanism in released Safari versions to enable and disable features for their own testing needs. They remain in the menu until the Experimental Feature menu support is removed. Safari releases also include the Experimental Features menu with experimental features that are enabled by default. When they are ready to be tested and used, they become enabled by default. Experimental features that are not ready for developer testing are disabled by default. It also gives WebKit engineers a mechanism to enable or disable certain features for testing during development. Options that appear in the Experimental Features menu, though accessible in Safari releases, is most useful for Safari Technology Preview where it allows web developers to try out in-development features and provide early feedback.
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