fix: scan window fix (cherry-pick)

lib/src/mobile_scanner.dart

@@ -6,6 +6,7 @@ import 'package:mobile_scanner/src/mobile_scanner_controller.dart';
 import 'package:mobile_scanner/src/mobile_scanner_exception.dart';
 import 'package:mobile_scanner/src/objects/barcode_capture.dart';
 import 'package:mobile_scanner/src/objects/mobile_scanner_arguments.dart';
+import 'package:mobile_scanner/src/scan_window_calculation.dart';
 
 /// The function signature for the error builder.
 typedef MobileScannerErrorBuilder = Widget Function(
@@ -175,75 +176,6 @@ class _MobileScannerState extends State<MobileScanner>
     }
   }
 
-  /// the [scanWindow] rect will be relative and scaled to the [widgetSize] not the texture. so it is possible,
-  /// depending on the [fit], for the [scanWindow] to partially or not at all overlap the [textureSize]
-  ///
-  /// since when using a [BoxFit] the content will always be centered on its parent. we can convert the rect
-  /// to be relative to the texture.
-  ///
-  /// since the textures size and the actuall image (on the texture size) might not be the same, we also need to
-  /// calculate the scanWindow in terms of percentages of the texture, not pixels.
-  Rect calculateScanWindowRelativeToTextureInPercentage(
-    BoxFit fit,
-    Rect scanWindow,
-    Size textureSize,
-    Size widgetSize,
-  ) {
-    double fittedTextureWidth;
-    double fittedTextureHeight;
-
-    switch (fit) {
-      case BoxFit.contain:
-        final widthRatio = widgetSize.width / textureSize.width;
-        final heightRatio = widgetSize.height / textureSize.height;
-        final scale = widthRatio < heightRatio ? widthRatio : heightRatio;
-        fittedTextureWidth = textureSize.width * scale;
-        fittedTextureHeight = textureSize.height * scale;
-        break;
-
-      case BoxFit.cover:
-        final widthRatio = widgetSize.width / textureSize.width;
-        final heightRatio = widgetSize.height / textureSize.height;
-        final scale = widthRatio > heightRatio ? widthRatio : heightRatio;
-        fittedTextureWidth = textureSize.width * scale;
-        fittedTextureHeight = textureSize.height * scale;
-        break;
-
-      case BoxFit.fill:
-        fittedTextureWidth = widgetSize.width;
-        fittedTextureHeight = widgetSize.height;
-        break;
-
-      case BoxFit.fitHeight:
-        final ratio = widgetSize.height / textureSize.height;
-        fittedTextureWidth = textureSize.width * ratio;
-        fittedTextureHeight = widgetSize.height;
-        break;
-
-      case BoxFit.fitWidth:
-        final ratio = widgetSize.width / textureSize.width;
-        fittedTextureWidth = widgetSize.width;
-        fittedTextureHeight = textureSize.height * ratio;
-        break;
-
-      case BoxFit.none:
-      case BoxFit.scaleDown:
-        fittedTextureWidth = textureSize.width;
-        fittedTextureHeight = textureSize.height;
-        break;
-    }
-
-    final offsetX = (widgetSize.width - fittedTextureWidth) / 2;
-    final offsetY = (widgetSize.height - fittedTextureHeight) / 2;
-
-    final left = (scanWindow.left - offsetX) / fittedTextureWidth;
-    final top = (scanWindow.top - offsetY) / fittedTextureHeight;
-    final right = (scanWindow.right - offsetX) / fittedTextureWidth;
-    final bottom = (scanWindow.bottom - offsetY) / fittedTextureHeight;
-
-    return Rect.fromLTRB(left, top, right, bottom);
-  }
-
   Rect? scanWindow;
 
   @override
@@ -261,8 +193,8 @@ class _MobileScannerState extends State<MobileScanner>
               scanWindow = calculateScanWindowRelativeToTextureInPercentage(
                 widget.fit,
                 widget.scanWindow!,
-                value.size,
-                Size(constraints.maxWidth, constraints.maxHeight),
+                textureSize: value.size,
+                widgetSize: constraints.biggest,
               );
 
               _controller.updateScanWindow(scanWindow);

lib/src/scan_window_calculation.dart

@@ -0,0 +1,97 @@
+import 'dart:math';
+
+import 'package:flutter/rendering.dart';
+
+/// Calculate the scan window rectangle relative to the texture size.
+///
+/// The [scanWindow] rectangle will be relative and scaled to [widgetSize], not [textureSize].
+/// Depending on the given [fit], the [scanWindow] can partially overlap the [textureSize],
+/// or not at all.
+///
+/// Due to using [BoxFit] the content will always be centered on its parent,
+/// which enables converting the rectangle to be relative to the texture.
+///
+/// Because the size of the actual texture and the size of the texture in widget-space
+/// can be different, calculate the size of the scan window in percentages,
+/// rather than pixels.
+///
+/// Returns a [Rect] that represents the position and size of the scan window in the texture.
+Rect calculateScanWindowRelativeToTextureInPercentage(
+  BoxFit fit,
+  Rect scanWindow, {
+  required Size textureSize,
+  required Size widgetSize,
+}) {
+  // Convert the texture size to a size in widget-space, with the box fit applied.
+  final fittedTextureSize = applyBoxFit(fit, textureSize, widgetSize);
+
+  // Get the correct scaling values depending on the given BoxFit mode
+  double sx = fittedTextureSize.destination.width / textureSize.width;
+  double sy = fittedTextureSize.destination.height / textureSize.height;
+
+  switch (fit) {
+    case BoxFit.fill:
+      // No-op, just use sx and sy.
+      break;
+    case BoxFit.contain:
+      final s = min(sx, sy);
+      sx = s;
+      sy = s;
+      break;
+    case BoxFit.cover:
+      final s = max(sx, sy);
+      sx = s;
+      sy = s;
+      break;
+    case BoxFit.fitWidth:
+      sy = sx;
+      break;
+    case BoxFit.fitHeight:
+      sx = sy;
+      break;
+    case BoxFit.none:
+      sx = 1.0;
+      sy = 1.0;
+      break;
+    case BoxFit.scaleDown:
+      final s = min(sx, sy);
+      sx = s;
+      sy = s;
+      break;
+  }
+
+  // Fit the texture size to the widget rectangle given by the scaling values above.
+  final textureWindow = Alignment.center.inscribe(
+    Size(textureSize.width * sx, textureSize.height * sy),
+    Rect.fromLTWH(0, 0, widgetSize.width, widgetSize.height),
+  );
+
+  // Transform the scan window from widget coordinates to texture coordinates.
+  final scanWindowInTexSpace = Rect.fromLTRB(
+    (1 / sx) * (scanWindow.left - textureWindow.left),
+    (1 / sy) * (scanWindow.top - textureWindow.top),
+    (1 / sx) * (scanWindow.right - textureWindow.left),
+    (1 / sy) * (scanWindow.bottom - textureWindow.top),
+  );
+
+  // Clip the scan window in texture coordinates with the texture bounds.
+  // This prevents percentages outside the range [0; 1].
+  final clippedScanWndInTexSpace = scanWindowInTexSpace.intersect(
+    Rect.fromLTWH(0, 0, textureSize.width, textureSize.height),
+  );
+
+  // Compute relative rectangle coordinates,
+  // with respect to the texture size, i.e. scan image.
+  final percentageLeft = clippedScanWndInTexSpace.left / textureSize.width;
+  final percentageTop = clippedScanWndInTexSpace.top / textureSize.height;
+  final percentageRight = clippedScanWndInTexSpace.right / textureSize.width;
+  final percentageBottom = clippedScanWndInTexSpace.bottom / textureSize.height;
+
+  // This rectangle can be used to cut out a rectangle of the scan image.
+  return Rect.fromLTRB(
+    percentageLeft,
+    percentageTop,
+    percentageRight,
+    percentageBottom,
+  );
+}

test/scan_window_test.dart

@@ -0,0 +1,182 @@
+import 'package:flutter/painting.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:mobile_scanner/src/scan_window_calculation.dart';
+
+void main() {
+  group(
+    'Scan window relative to texture',
+    () {
+      group('Widget (landscape) smaller than texture (portrait)', () {
+        const textureSize = Size(480.0, 640.0);
+        const widgetSize = Size(432.0, 256.0);
+        final ctx = ScanWindowTestContext(
+          textureSize: textureSize,
+          widgetSize: widgetSize,
+          scanWindow: Rect.fromLTWH(
+            widgetSize.width / 4,
+            widgetSize.height / 4,
+            widgetSize.width / 2,
+            widgetSize.height / 2,
+          ),
+        );
+
+        test('wl tp: BoxFit.none', () {
+          ctx.testScanWindow(
+            BoxFit.none,
+            const Rect.fromLTRB(0.275, 0.4, 0.725, 0.6),
+          );
+        });
+
+        test('wl tp: BoxFit.fill', () {
+          ctx.testScanWindow(
+            BoxFit.fill,
+            const Rect.fromLTRB(0.25, 0.25, 0.75, 0.75),
+          );
+        });
+
+        test('wl tp: BoxFit.fitHeight', () {
+          ctx.testScanWindow(
+            BoxFit.fitHeight,
+            const Rect.fromLTRB(0.0, 0.25, 1.0, 0.75),
+          );
+        });
+
+        test('wl tp: BoxFit.fitWidth', () {
+          ctx.testScanWindow(
+            BoxFit.fitWidth,
+            const Rect.fromLTRB(
+              0.25,
+              0.38888888888888895,
+              0.75,
+              0.6111111111111112,
+            ),
+          );
+        });
+
+        test('wl tp: BoxFit.cover', () {
+          // equal to fitWidth
+          ctx.testScanWindow(
+            BoxFit.cover,
+            const Rect.fromLTRB(
+              0.25,
+              0.38888888888888895,
+              0.75,
+              0.6111111111111112,
+            ),
+          );
+        });
+
+        test('wl tp: BoxFit.contain', () {
+          // equal to fitHeigth
+          ctx.testScanWindow(
+            BoxFit.contain,
+            const Rect.fromLTRB(0.0, 0.25, 1.0, 0.75),
+          );
+        });
+
+        test('wl tp: BoxFit.scaleDown', () {
+          // equal to fitHeigth, contain
+          ctx.testScanWindow(
+            BoxFit.scaleDown,
+            const Rect.fromLTRB(0.0, 0.25, 1.0, 0.75),
+          );
+        });
+      });
+
+      group('Widget (landscape) smaller than texture and texture (landscape)',
+          () {
+        const textureSize = Size(640.0, 480.0);
+        const widgetSize = Size(320.0, 120.0);
+        final ctx = ScanWindowTestContext(
+          textureSize: textureSize,
+          widgetSize: widgetSize,
+          scanWindow: Rect.fromLTWH(
+            widgetSize.width / 4,
+            widgetSize.height / 4,
+            widgetSize.width / 2,
+            widgetSize.height / 2,
+          ),
+        );
+
+        test('wl tl: BoxFit.none', () {
+          ctx.testScanWindow(
+            BoxFit.none,
+            const Rect.fromLTRB(0.375, 0.4375, 0.625, 0.5625),
+          );
+        });
+
+        test('wl tl: BoxFit.fill', () {
+          ctx.testScanWindow(
+            BoxFit.fill,
+            const Rect.fromLTRB(0.25, 0.25, 0.75, 0.75),
+          );
+        });
+
+        test('wl tl: BoxFit.fitHeight', () {
+          ctx.testScanWindow(
+            BoxFit.fitHeight,
+            const Rect.fromLTRB(0.0, 0.25, 1.0, 0.75),
+          );
+        });
+
+        test('wl tl: BoxFit.fitWidth', () {
+          ctx.testScanWindow(
+            BoxFit.fitWidth,
+            const Rect.fromLTRB(0.25, 0.375, 0.75, 0.625),
+          );
+        });
+
+        test('wl tl: BoxFit.cover', () {
+          // equal to fitWidth
+          ctx.testScanWindow(
+            BoxFit.cover,
+            const Rect.fromLTRB(0.25, 0.375, 0.75, 0.625),
+          );
+        });
+
+        test('wl tl: BoxFit.contain', () {
+          // equal to fitHeigth
+          ctx.testScanWindow(
+            BoxFit.contain,
+            const Rect.fromLTRB(0.0, 0.25, 1.0, 0.75),
+          );
+        });
+
+        test('wl tl: BoxFit.scaleDown', () {
+          // equal to fitHeigth, contain
+          ctx.testScanWindow(
+            BoxFit.scaleDown,
+            const Rect.fromLTRB(0.0, 0.25, 1.0, 0.75),
+          );
+        });
+      });
+    },
+  );
+}
+
+class ScanWindowTestContext {
+  ScanWindowTestContext({
+    required this.textureSize,
+    required this.widgetSize,
+    required this.scanWindow,
+  });
+
+  final Size textureSize;
+  final Size widgetSize;
+  final Rect scanWindow;
+
+  void testScanWindow(BoxFit fit, Rect expected) {
+    final actual = calculateScanWindowRelativeToTextureInPercentage(
+      fit,
+      scanWindow,
+      textureSize: textureSize,
+      widgetSize: widgetSize,
+    );
+
+    // don't use expect(actual, expected) because Rect.toString() only shows one digit after the comma which can be confusing
+    expect(actual.left, expected.left);
+    expect(actual.top, expected.top);
+    expect(actual.right, expected.right);
+    expect(actual.bottom, expected.bottom);
+  }
+}