bug: ion-segment scrollable IOS animation bug

[rostislavcz]

Prerequisites

• [X] I have read the Contributing Guidelines.
• [X] I agree to follow the Code of Conduct.
• [X] I have searched for existing issues that already report this problem, without success.

Ionic Framework Version

v7.x, v8.x

Current Behavior

When you use multiple segment items there is strange animation bug on ios devices when using scrollable option. (Android, Web - even Safari works fine)

<IonSegment scrollable={true} value="heart">
  <IonSegmentButton value="home">
    <IonIcon icon={home}></IonIcon>
  </IonSegmentButton>
  <IonSegmentButton value="heart">
    <IonIcon icon={heart}></IonIcon>
  </IonSegmentButton>
  <IonSegmentButton value="pin">
    <IonIcon icon={pin}></IonIcon>
  </IonSegmentButton>
  <IonSegmentButton value="star">
    <IonIcon icon={star}></IonIcon>
  </IonSegmentButton>
</IonSegment>

Here you can see the result on real device, i did a little CSS changes but tried also with original styles and there is the same result. I also did a little digging in your code and managed to solve the problem:

In Segment class there is method

private scrollActiveButtonIntoView(smoothScroll = true) {
  const { scrollable, value, el } = this;

  if (scrollable) {
    const buttons = this.getButtons();
    const activeButton = buttons.find((button) => button.value === value);
    if (activeButton !== undefined) {
      const scrollContainerBox = el.getBoundingClientRect();
      const activeButtonBox = activeButton.getBoundingClientRect();

      /**
        * Subtract the active button x position from the scroll
        * container x position. This will give us the x position
        * of the active button within the scroll container.
        */
      const activeButtonLeft = activeButtonBox.x - scrollContainerBox.x;

      /**
        * If we just used activeButtonLeft, then the active button
        * would be aligned with the left edge of the scroll container.
        * Instead, we want the segment button to be centered. As a result,
        * we subtract half of the scroll container width. This will position
        * the left edge of the active button at the midpoint of the scroll container.
        * We then add half of the active button width. This will position the active
        * button such that the midpoint of the active button is at the midpoint of the
        * scroll container.
        */
      const centeredX = activeButtonLeft - scrollContainerBox.width / 2 + activeButtonBox.width / 2;

      /**
        * We intentionally use scrollBy here instead of scrollIntoView
        * to avoid a WebKit bug where accelerated animations break
        * when using scrollIntoView. Using scrollIntoView will cause the
        * segment container to jump during the transition and then snap into place.
        * This is because scrollIntoView can potentially cause parent element
        * containers to also scroll. scrollBy does not have this same behavior, so
        * we use this API instead.
        *
        * Note that if there is not enough scrolling space to center the element
        * within the scroll container, the browser will attempt
        * to center by as much as it can.
        */
      el.scrollBy({
        top: 0,
        left: centeredX,
        behavior: smoothScroll ? 'smooth' : 'instant',
      });
    }
  }
}

Instead of el.scrollBy if I call el.scrollTo, the problem dissapears and it works as it should

https://github.com/ionic-team/ionic-framework/assets/58735164/21208d4d-bfd9-47ed-a74a-dcc45165b2e0

Expected Behavior

The same result when you just change el.scrollBy to el.scrollTo

https://github.com/ionic-team/ionic-framework/assets/58735164/1a0af05f-a8f2-440e-8811-03804e6893eb

Steps to Reproduce

Run any basic Ionic/Capacitor project on ios device and use scrollable ion-segment with multiple items, that will has width more than 100% of device width

Code Reproduction URL

https://stackblitz.com/edit/dw3jre?file=package.json

Ionic Info

Ionic:

Ionic CLI : 7.0.1 (/usr/local/lib/node_modules/@ionic/cli) Ionic Framework : @ionic/angular 8.0.0 @angular-devkit/build-angular : 17.3.5 @angular-devkit/schematics : 17.3.5 @angular/cli : 17.3.5 @ionic/angular-toolkit : 11.0.1

Capacitor:

Capacitor CLI : 6.0.0 @capacitor/android : 6.0.0 @capacitor/core : 6.0.0 @capacitor/ios : 6.0.0

Utility:

cordova-res : 0.15.4 native-run : 2.0.1

Additional Information

No response