leaf_widgets

Leaf UI widgets — zero external dependencies.

• LeafViewer — a self-contained, photo_view-style fullscreen viewer: clamped zoom + pan, swipe-to-dismiss, double-tap zoom, mouse-wheel zoom, native keyboard controls and tap-outside dismissal. Desktop + mobile behaviour out of the box.
• LeafZoomable — opt-in per-page zoom wrapper for LeafViewer (also usable standalone); auto-sizes itself from an image's pixel dimensions via LeafZoomable.image.
• LeafZoomController — the zoom/pan state machine behind both (clamped, fling, double-tap staging, wheel zoom).
• Plus: LeafContextMenu, LeafPopover, LeafImage, AnimatedFavoriteButton, AnimatedStar.

Features

• Clamped zoom (1x–maxScale) and pan (corners cannot escape the viewport)
• Edge-release: a drag at a fully zoomed-out, fully clamped position pages or dismisses instead of panning (gesture-arena based, no raw pointer routing)
• Mobile: swipe to page, drag perpendicular to dismiss, double-tap zooms (1x → contained → 1:1 when dimensions are known)
• Desktop (Windows/Linux/macOS): mouse-wheel zoom (cursor-anchored), no drag paging/dismiss/double-tap by default, default on-screen controls (previous/next, close, page counter) — or your own via controlsBuilder
• Keyboard when focused: ←/→ (or ↑/↓ for vertical paging) + Esc dismiss (opt-out with enableKeyboard: false)
• Tap outside the active image fires onTapOutside
• LeafZoomable.image: pixel dimensions extracted from the image stream at load time — contained size and 1:1 double-tap step work without passing anything (falls back to viewport clamping until decoded)

Getting started

Add to pubspec.yaml:

dependencies:
  leaf_widgets:
    path: ../leaf_widgets

Usage

import 'package:flutter/material.dart';
import 'package:leaf_widgets/leaf_widgets.dart';

class PostViewer extends StatelessWidget {
  const PostViewer({super.key, required this.posts});

  final List<String> urls;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.black,
      body: LeafViewer(
        pageCount: urls.length,
        onDismissed: () => Navigator.of(context).maybePop(),
        pageBuilder: (context, index) => LeafZoomable.image(
          image: Image.network(
            urls[index],
            fit: BoxFit.contain,
            errorBuilder: (context, error, stackTrace) =>
                const Center(child: Icon(Icons.broken_image, color: Colors.white38)),
          ),
        ),
      ),
    );
  }
}

That is the full viewer: paging, clamped zoom/pan, swipe-dismiss, double-tap (1:1 included — the pixel dimensions are resolved automatically), wheel zoom, keyboard, tap-outside, and desktop controls.

Sizing control

LeafZoomable sizes the zoom clamp itself when possible:

• LeafZoomable.image resolves the image's pixel dimensions from its stream (no second download — the image cache dedupes) and uses them for the contained size and the 1:1 stage.
• Plain LeafZoomable(child: ...) clamps against the viewport until you pass explicit sizes:

// Contained (fit-to-screen) render size + full-resolution size.
LeafZoomable(
  childSize: myContainedSize,   // optional — defaults to the viewport
  originalSize: myFullSize,     // optional — null disables the 1:1 stage
  child: myWidget,
)

Custom chrome

LeafViewer(
  pageCount: urls.length,
  controlsBuilder: (context, controls) => Row(
    children: [
      IconButton(
        onPressed: controls.canGoPrevious ? () => controls.goToPage(controls.currentIndex - 1) : null,
        icon: const Icon(Icons.chevron_left),
      ),
      Text('${controls.currentIndex + 1} / ${controls.pageCount}'),
    ],
  ),
  pageBuilder: (context, index) => /* ... */,
)

Platforms

• Touch: swipe paging, perpendicular drag dismiss, double-tap zoom.
• Desktop: wheel zoom, keyboard, default controls; swipe gestures are off unless enableSwipeGestures: true forces them on.
• scrollDirection flips paging to vertical; the dismiss gesture then runs along the other axis.

Additional information

• Example: example/lib/viewer_demo.dart
• All viewer code lives in lib/src/viewer/ — zoom math in leaf_zoom_controller.dart (property-tested), gesture arbitration in leaf_pan_zoom_recognizer.dart (ported from photo_view, MIT).