Open3

ブラウザのタッチジェスチャについて

やまやま

PCのブラウザにデフォルトで用意されている「拡大・縮小」ボタンやCtrl +/-による拡大・縮小と，タッチパッドやタッチパネルを用いたピンチアウト・ピンチインジェスチャによる拡大・縮小は性質が異なる。
前者はページレイアウトにも影響を与え，しばしばレイアウトを崩してしまうこともあるが，後者はベクタ画像の拡大のように，表示領域をそのままの形で拡大してくれる。

これらの違いはどこから生まれるのだろうか？
これらの違いを知れば，Ctrl +/-によって，タッチジェスチャのような拡大・縮小を実現するブラウザ拡張機能も作れるのではないか？

ということで，ChatGPTに聞いてみたことをメモ。

やまやま

ChatGPTにこれらの違いはどこのレイヤーで生まれるのか？を質問した結果。

The differences between using keyboard shortcuts (Ctrl + and Ctrl -) and touch gestures (pinch in and pinch out) for zooming on a webpage arise from how these interactions are processed and their intended effects. Here’s a detailed explanation of these differences:

Keyboard Shortcuts (Ctrl + and Ctrl -)

How it Works:

  • Browser-Level Zoom: When you press Ctrl + or Ctrl -, the browser adjusts the zoom level of the entire webpage. This is a feature built into web browsers like Chrome, Firefox, and Edge.
  • Scaling the Page: This zoom method effectively scales the entire page, including text, images, and other elements. The browser increases or decreases the size of everything proportionally.
  • Layout Reflow: Because the entire page is scaled, it can cause reflow or re-layout of the content. Elements may wrap differently, containers may resize, and the overall layout might change. This can lead to a "broken" layout if the page isn’t responsive or designed to handle such zoom changes.
  • Persistent Zoom Level: The zoom level set using Ctrl + or Ctrl - persists across sessions for the specific website until changed again.

Touch Gestures (Pinch In and Pinch Out)

How it Works:

  • Viewport Zoom: Pinch gestures are typically interpreted by the operating system or the browser’s touch interface. They manipulate the viewport of the browser, essentially acting as a magnifying glass.
  • CSS Transformations: In many cases, pinch gestures apply a CSS transformation to scale the content. This can be similar to the effect of zooming into a section of a vector graphic, where the contents become larger and potentially clearer, without triggering a layout reflow.
  • Non-Persistent Zoom: Unlike Ctrl +/-, the zoom level from pinch gestures usually does not persist across sessions or page reloads. It’s more transient and specific to the user’s current interaction.
  • Independent of Layout: Since it’s more like magnifying the content rather than scaling it proportionally, the layout generally remains intact. Elements do not reflow or change their positions; they simply appear larger or smaller.

Technical Differences

Event Handling:

  • OS Level vs Browser Level: Pinch gestures are often handled at the OS level or by the device drivers that manage touch input. The OS then communicates this to the application (browser), which handles the gesture by modifying the viewport or applying CSS transformations.
  • Browser’s Role: The browser’s internal event handling system also distinguishes between keyboard inputs and touch gestures. Specific JavaScript events are dispatched for different types of interactions:
    • Keyboard Events: keydown, keyup, etc.
    • Touch Events: touchstart, touchmove, touchend, etc.

Callback Processing:

  • Separate Callbacks: Browsers have different callback mechanisms for keyboard shortcuts and touch gestures. For instance, the zoom event for Ctrl +/Ctrl - versus gesturechange, gesturestart, and gestureend for touch gestures.
  • Rendering Pipeline: The rendering and reflow engine of the browser processes these inputs differently. Keyboard zoom affects the entire rendering pipeline, causing a full re-render at a different scale. In contrast, touch gesture zooms adjust the CSS transform properties or the viewport scale, which might not trigger a full reflow.

Conclusion

The difference in behavior between Ctrl +/Ctrl - and pinch gestures is rooted in how these interactions are captured and processed by the OS and the browser. Keyboard shortcuts cause a complete rescaling of the webpage, often leading to layout changes, while touch gestures generally result in a viewport zoom, which magnifies content without altering the layout.

References

These references provide additional insights into how different zoom mechanisms work in web browsers.

やまやま

質問:
so the handlers of touch gestures (pinch in/pinch out, etc.) internally use the transform attribute in CSS to achieve such behaviors, right?

Yes, the browser handles touch gestures such as pinch in and pinch out by adjusting the CSS transformation properties, specifically the transform: scale property. This allows the browser to zoom in and out on content without affecting the layout of the page.

How Touch Gestures Are Handled

  1. Viewport Meta Tag:

    • Browsers interpret pinch-to-zoom gestures and often adjust the viewport based on the meta viewport tag settings in the HTML. This tag controls the layout viewport, which can be scaled using pinch gestures.
    • Example: <meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=3, user-scalable=yes">

  2. CSS Transformations:

    • When a pinch gesture is detected, browsers apply a CSS transform: scale property to the elements within the viewport. This scaling is similar to using a zoom lens on the content, making it larger or smaller without altering the actual dimensions or layout.
    • The transform: scale property changes the rendering of the element in a way that magnifies it, which can include text, images, and other components, making them appear larger or smaller.

Implementation in JavaScript

Browsers can dispatch specific events for touch gestures such as touchstart, touchmove, and touchend. JavaScript can listen to these events and apply CSS transformations dynamically.

Example:

element.addEventListener('touchmove', function(event) {
  if (event.scale !== 1) {
    element.style.transform = `scale(${event.scale})`;
  }
});

References

By leveraging these properties and events, browsers achieve smooth, non-intrusive zooming behavior that does not disrupt the overall layout of the web page.