Added histogram and separated camera view builder

lib/screens/metering/components/camera_container/components/camera_preview/components/camera_view/widget_camera_view.dart

@@ -14,10 +14,12 @@ class CameraView extends StatelessWidget {
       valueListenable: controller,
       builder: (_, __, ___) => AspectRatio(
         aspectRatio: _isLandscape(value) ? value.aspectRatio : (1 / value.aspectRatio),
-        child: RotatedBox(
+        child: value.isInitialized
+            ? RotatedBox(
                 quarterTurns: _getQuarterTurns(value),
                 child: controller.buildPreview(),
-        ),
+              )
+            : const SizedBox.shrink(),
       ),
     );
   }

lib/screens/metering/components/camera_container/components/camera_preview/components/histogram/widget_histogram.dart

@@ -0,0 +1,132 @@
+import 'dart:math';
+
+import 'package:camera/camera.dart';
+import 'package:flutter/material.dart';
+import 'package:lightmeter/res/dimens.dart';
+
+class CameraHistogram extends StatefulWidget {
+  final CameraController controller;
+
+  const CameraHistogram({required this.controller, super.key});
+
+  @override
+  _CameraHistogramState createState() => _CameraHistogramState();
+}
+
+class _CameraHistogramState extends State<CameraHistogram> {
+  List<int> histogramR = List.filled(256, 0);
+  List<int> histogramG = List.filled(256, 0);
+  List<int> histogramB = List.filled(256, 0);
+
+  @override
+  void initState() {
+    super.initState();
+    WidgetsBinding.instance.addPostFrameCallback((_) {
+      _startImageStream();
+    });
+  }
+
+  @override
+  void dispose() {
+    widget.controller.stopImageStream();
+    super.dispose();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return Column(
+      crossAxisAlignment: CrossAxisAlignment.stretch,
+      mainAxisSize: MainAxisSize.min,
+      children: [
+        HistogramChannel(
+          color: Colors.red,
+          values: histogramR,
+        ),
+        const SizedBox(height: Dimens.grid4),
+        HistogramChannel(
+          color: Colors.green,
+          values: histogramG,
+        ),
+        const SizedBox(height: Dimens.grid4),
+        HistogramChannel(
+          color: Colors.blue,
+          values: histogramB,
+        ),
+      ],
+    );
+  }
+
+  void _startImageStream() {
+    widget.controller.startImageStream((CameraImage image) {
+      histogramR = List.filled(256, 0);
+      histogramG = List.filled(256, 0);
+      histogramB = List.filled(256, 0);
+
+      final int uvRowStride = image.planes[1].bytesPerRow;
+      final int uvPixelStride = image.planes[1].bytesPerPixel!;
+
+      for (int x = 0; x < image.width; x++) {
+        for (int y = 0; y < image.height; y++) {
+          final int uvIndex = uvPixelStride * (x / 2).floor() + uvRowStride * (y / 2).floor();
+          final int index = y * image.width + x;
+
+          final yp = image.planes[0].bytes[index];
+          final up = image.planes[1].bytes[uvIndex];
+          final vp = image.planes[2].bytes[uvIndex];
+
+          final r = yp + vp * 1436 / 1024 - 179;
+          final g = yp - up * 46549 / 131072 + 44 - vp * 93604 / 131072 + 91;
+          final b = yp + up * 1814 / 1024 - 227;
+
+          histogramR[r.round().clamp(0, 255)]++;
+          histogramG[g.round().clamp(0, 255)]++;
+          histogramB[b.round().clamp(0, 255)]++;
+        }
+      }
+
+      if (mounted) setState(() {});
+    });
+  }
+}
+
+class HistogramChannel extends StatelessWidget {
+  final List<int> values;
+  final Color color;
+
+  final int _maxOccurences;
+
+  HistogramChannel({
+    required this.values,
+    required this.color,
+    super.key,
+  }) : _maxOccurences = values.reduce((value, element) => max(value, element));
+
+  @override
+  Widget build(BuildContext context) {
+    return LayoutBuilder(
+      builder: (context, constraints) {
+        final pixelWidth = constraints.maxWidth / values.length;
+        return Column(
+          children: [
+            SizedBox(
+              height: Dimens.grid16,
+              child: Row(
+                crossAxisAlignment: CrossAxisAlignment.end,
+                children: values
+                    .map(
+                      (e) => SizedBox(
+                        height: _maxOccurences == 0 ? 0 : Dimens.grid16 * (e / _maxOccurences),
+                        width: pixelWidth,
+                        child: ColoredBox(color: color),
+                      ),
+                    )
+                    .toList(),
+              ),
+            ),
+            const Divider(),
+          ],
+        );
+      },
+    );
+  }
+}

lib/screens/metering/components/camera_container/components/camera_preview/widget_camera_preview.dart

@@ -0,0 +1,56 @@
+import 'package:camera/camera.dart';
+import 'package:flutter/material.dart';
+import 'package:lightmeter/platform_config.dart';
+import 'package:lightmeter/res/dimens.dart';
+import 'package:lightmeter/screens/metering/components/camera_container/components/camera_preview/components/camera_view/widget_camera_view.dart';
+import 'package:lightmeter/screens/metering/components/camera_container/components/camera_preview/components/camera_view_placeholder/widget_placeholder_camera_view.dart';
+import 'package:lightmeter/screens/metering/components/camera_container/components/camera_preview/components/histogram/widget_histogram.dart';
+import 'package:lightmeter/screens/metering/components/camera_container/models/camera_error_type.dart';
+
+class CameraPreview extends StatefulWidget {
+  final CameraController? controller;
+  final CameraErrorType? error;
+
+  const CameraPreview({this.controller, this.error, super.key});
+
+  @override
+  State<CameraPreview> createState() => _CameraPreviewState();
+}
+
+class _CameraPreviewState extends State<CameraPreview> {
+  @override
+  Widget build(BuildContext context) {
+    return AspectRatio(
+      aspectRatio: PlatformConfig.cameraPreviewAspectRatio,
+      child: Center(
+        child: Stack(
+          children: [
+            const CameraViewPlaceholder(error: null),
+            AnimatedSwitcher(
+              duration: Dimens.switchDuration,
+              child: widget.controller != null
+                  ? ValueListenableBuilder<CameraValue>(
+                      valueListenable: widget.controller!,
+                      builder: (_, __, ___) => Stack(
+                        alignment: Alignment.bottomCenter,
+                        children: [
+                          if (widget.controller!.value.isInitialized)
+                            CameraView(controller: widget.controller!),
+                          if (widget.controller!.value.isInitialized)
+                            Positioned(
+                              left: 0,
+                              right: 0,
+                              bottom: Dimens.borderRadiusM,
+                              child: CameraHistogram(controller: widget.controller!),
+                            ),
+                        ],
+                      ),
+                    )
+                  : CameraViewPlaceholder(error: widget.error),
+            ),
+          ],
+        ),
+      ),
+    );
+  }
+}

lib/screens/metering/components/camera_container/widget_container_camera.dart

@@ -10,8 +10,7 @@ import 'package:lightmeter/res/dimens.dart';
 import 'package:lightmeter/screens/metering/components/camera_container/bloc_container_camera.dart';
 import 'package:lightmeter/screens/metering/components/camera_container/components/camera_controls/widget_camera_controls.dart';
 import 'package:lightmeter/screens/metering/components/camera_container/components/camera_controls_placeholder/widget_placeholder_camera_controls.dart';
-import 'package:lightmeter/screens/metering/components/camera_container/components/camera_view/widget_camera_view.dart';
+import 'package:lightmeter/screens/metering/components/camera_container/components/camera_preview/widget_camera_preview.dart';
-import 'package:lightmeter/screens/metering/components/camera_container/components/camera_view_placeholder/widget_placeholder_camera_view.dart';
 import 'package:lightmeter/screens/metering/components/camera_container/event_container_camera.dart';
 import 'package:lightmeter/screens/metering/components/camera_container/models/camera_error_type.dart';
 import 'package:lightmeter/screens/metering/components/camera_container/state_container_camera.dart';
@@ -107,20 +106,11 @@ class _CameraViewBuilder extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    return AspectRatio(
+    return BlocBuilder<CameraContainerBloc, CameraContainerState>(
-      aspectRatio: PlatformConfig.cameraPreviewAspectRatio,
-      child: BlocBuilder<CameraContainerBloc, CameraContainerState>(
       buildWhen: (previous, current) => current is! CameraActiveState,
-        builder: (context, state) => Center(
+      builder: (context, state) => CameraPreview(
-          child: AnimatedSwitcher(
+        controller: state is CameraInitializedState ? state.controller : null,
-            duration: Dimens.durationM,
+        error: state is CameraErrorState ? state.error : null,
-            child: switch (state) {
-              CameraInitializedState() => CameraView(controller: state.controller),
-              CameraErrorState() => CameraViewPlaceholder(error: state.error),
-              _ => const CameraViewPlaceholder(error: null),
-            },
-          ),
-        ),
       ),
     );
   }
@@ -161,7 +151,9 @@ class _CameraControlsBuilder extends StatelessWidget {
               },
             );
           } else {
-            child = const Column(children: [Expanded(child: SizedBox.shrink())],);
+            child = const Column(
+              children: [Expanded(child: SizedBox.shrink())],
+            );
           }
 
           return AnimatedSwitcher(