There's more to performance than meets the eye

Leonie Watson, The Paciello Group (TPG)

There's more to performance than meets the eye

DeltaV, London May 2018

Léonie Watson ~

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Web performance

The speed at which web pages are downloaded and displayed in the user's browser

Browsers

Chrome Edge Firefox Safari
Chrome Edge Firefox Safari
(Google) (Microsoft) (Mozilla) (Apple)

Screen readers

Jaws NVDA Voiceover Narrator Orca
Jaws NVDA Voiceover Narrator Orca
(Freedom Scientific) (NV Access) (Apple) (Microsoft) (GNOME)

Screen reader demo: text

Screen reader demo: language

In the late 90s

Screen readers consumed the HTML directly from the browser, and created a virtual model of the content

Screen reader demo: headings

Screen reader demo: buttons

In the early 00s

Screen readers began using accessibility APIs to query information from the browser

Accessibility APIs

Windows MacOS Linux
UI Automation (UIA)
MS Active Accessibility (MSAA)
IAccessible2 (IA2)
OSX Accessibility Protocol (AXAPI) Accessibility Toolkit (ATK)
AT Service Provider Interface (AT-SPI)

The details & summary elements

<details>
<summary>Tequila...</summary>
Makes me happy!
</details>

Edge: not implemented

details/summary elements in Edge

Firefox: implemented

The accessibility tree: details element

Role
button
State
focusable
focused
expandable
collapsed

Screen reader demo: details & summary elements

In the late 10s

All screen readers use accessibility APIs to query information from the browser, but not all create a virtual model of the content

Single process model

Single browser process that managed the application, content, and other common tasks

Multi-process model

Separate application process, one or more content processes, and processes for handling other common tasks

Communication architectures

In-process communication
Screen reader injects itself into the application process, and communicates directly with the browser
Out-of-process communication
Screen reader communicates with the browser across application boundaries

Multi-process: IE

Windows IE

Screen reader injects into the application process, and has direct access to the content process

IE: approach

IE

Accessibility API calls made directly into the content process

IE: accessibility performance

IE Jaws NVDA

Fast Time To Interaction (TTI) and subsequent performance, but prone to instability

Multi-process: Chrome & firefox

Windows Chrome Firefox

Screen reader injects into the application process, but does not have direct access to the content process

Chrome: initial approach

Chrome

Proxied accessibility API calls from the application process into the content process

Chrome: current approach

Chrome

Caches a copy of the accessibility tree in the application process

Chrome: accessibility performance

Chrome Jaws NVDA

Possible slow TTI, but fast subsequent performance

Chrome: screen reader TTI

Firefox: approach

Firefox

Proxies accessibility API calls from the application process into the content process, but uses intelligent caching

Firefox: accessibility performance

Firefox Jaws NVDA

Good TTI and subsequent performance, but accessibility performance issues introduced with Quantum remain unresolved

Multi-process: Edge

Windows Edge

Screen readers cannot inject into the application process, and do not have access to the content process

Edge: approach

Edge

No caching, all accessibility API requests are handled via the OS

Edge: accessibility performance

Edge Jaws NVDA Narrator

Fast TTI, but possible slow subsequent performance

Edge: Jaws & NVDA

Edge Jaws NVDA

Out-of-process calls are 12 to 50 times slower than in-process calls, making a performant virtual model impossible

Edge: Narrator

Edge Narrator

Narrator is integrated into the OS, and does not use a virtual model, so is reasonably performant

Safari: VoiceOver

Edge Narrator

VoiceOver is also integrated into the OS, and does not use a virtual model, so is reasonably performant

Performance: drop the virtual model?

Screen readers depend on the virtual model to improve human performance

Screen reader demo: selecting content

Screen reader demo: select using placeholders

Performance: improve accessibility APIs

Accessibility APIs need the same features that screen readers have in the virtual model

Screen reader demo: searching with UIA

Performance: code well

Things that hit general performance will have an impact on accessibility performance

Thank you

To the following people, for answering many questions:

Screen reader demo: how it really is

There's more to performance than meets the eye

DeltaV, London May 2018

Léonie Watson ~

Mastodon
@[email protected]
Twitter
@LeonieWatson
Blog
tink.uk
Github
@LJWatson