Isolate the calculation of the histogram

kra-mo · Sep 18, 2024 · 187da6c · 187da6c
1 parent e092610
commit 187da6c
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Showing 3 changed files with 21 additions and 14 deletions.
diff --git a/lib/editor_page.dart b/lib/editor_page.dart
@@ -47,7 +47,7 @@ class _SlyEditorPageState extends State<SlyEditorPage> {
 
   late final SlyImage _originalImage = widget.image;
   late SlyImage _editedImage;
-  late Widget _histogram = getHistogram(_editedImage);
+  Widget? _histogram;
 
   Uint8List? _originalImageData;
   Uint8List? _editedImageData;
@@ -220,17 +220,19 @@ class _SlyEditorPageState extends State<SlyEditorPage> {
           _saveOnLoad = false;
         }
 
-        if (!mounted) return;
-        setState(() {
-          _histogram = getHistogram(_editedImage);
-        });
-
         _editedImage.encode(format: 'JPEG75').then((data) {
           if (!mounted) return;
           setState(() {
             _editedImageData = data;
           });
         });
+
+        getHistogram(_editedImage).then((data) {
+          if (!mounted) return;
+          setState(() {
+            _histogram = data;
+          });
+        });
     }
   }
 

diff --git a/lib/histogram.dart b/lib/histogram.dart
@@ -1,20 +1,19 @@
+import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 
 import 'package:fl_chart/fl_chart.dart';
 
 import 'image.dart';
 
-LineChart getHistogram(SlyImage image) {
-  final imageData = image.getHistogramData();
-
+LineChart _buildHistogram(Uint8List imagdeData) {
   final List<List<FlSpot>> spots = [
     List.generate(16, (index) => FlSpot(index.toDouble(), 0)),
     List.generate(16, (index) => FlSpot(index.toDouble(), 0)),
     List.generate(16, (index) => FlSpot(index.toDouble(), 0))
   ];
 
   int channel = 0;
-  for (int pixel in imageData) {
+  for (int pixel in imagdeData) {
     int i = pixel >> 4;
     if (i == 0 && pixel != 0) {
       i = 1;
@@ -67,3 +66,7 @@ LineChart getHistogram(SlyImage image) {
     ),
   );
 }
+
+Future<LineChart> getHistogram(SlyImage image) async {
+  return await compute(_buildHistogram, await image.getHistogramData());
+}
diff --git a/lib/image.dart b/lib/image.dart
@@ -325,11 +325,13 @@ class SlyImage {
 
   /// Returns a short list representing the RGB colors across the image,
   /// useful for building a histogram.
-  Uint8List getHistogramData() {
-    final resizedImage =
-        img.copyResize(_image, width: 20, height: 20).convert(numChannels: 3);
+  Future<Uint8List> getHistogramData() async {
+    final cmd = img.Command()
+      ..image(_image)
+      ..copyResize(width: 20, height: 20)
+      ..convert(numChannels: 3);
 
-    return resizedImage.buffer.asUint8List();
+    return (await cmd.executeThread()).outputImage!.buffer.asUint8List();
   }
 
   void dispose() {