update captcha solving algo

lib/page/login/jc_captcha.dart

@@ -1,12 +1,10 @@
 // Copyright 2023 BenderBlog Rodriguez and contributors.
 // SPDX-License-Identifier: MIT
 
-// http://thispage.tech:9680/jclee1995/flutter-jc-captcha/-/blob/master/lib/src/captcha_plugin_cn.dart
 // https://juejin.cn/post/7284608063914622995
 
 import 'dart:convert';
 import 'dart:io';
-import 'dart:math';
 import 'dart:typed_data';
 
 import 'package:dio/dio.dart';
@@ -99,52 +97,95 @@ class SliderCaptchaClientProvider {
     return result.data["errorCode"] == 1;
   }
 
-  static double? _trySolve(Uint8List puzzleData, Uint8List pieceData) {
+  static double? _trySolve(Uint8List puzzleData, Uint8List pieceData,
+      {int border = 24}) {
     img.Image? puzzle = img.decodeImage(puzzleData);
     if (puzzle == null) {
       return null;
     }
-
     img.Image? piece = img.decodeImage(pieceData);
     if (piece == null) {
       return null;
     }
 
-    // note that puzzle and piece have the same height
-
-    int minY = piece.height - 1;
-    int maxY = 0;
-
-    for (var y = 0; y < piece.height; y++) {
-      if (piece.getPixel((piece.width * 0.5).floor(), y).a > 0) {
-        minY = min(minY, y);
-        maxY = max(maxY, y);
+    var bbox = _findAlphaBoundingBox(piece);
+    int xL = bbox[0] + border;
+    int yT = bbox[1] + border;
+    int xR = bbox[2] - border;
+    int yB = bbox[3] - border;
+
+    var widthW = xR - xL;
+    var heightW = yB - yT;
+    var widthG = puzzle.width - piece.width + widthW - 1;
+
+    var meanT = _calculateMean(piece, xL, yT, widthW, heightW);
+    var templateN = _normalizeImage(piece, xL, yT, widthW, heightW, meanT);
+
+    double nccMax = 0;
+    int xMax = 0;
+    for (int x = xL + 1; x < widthG - widthW; x += 2) {
+      var meanW = _calculateMean(puzzle, x, yT, widthW, heightW);
+      var ncc = _calculateNCC(puzzle, x, yT, widthW, heightW, templateN, meanW);
+      if (ncc > nccMax) {
+        nccMax = ncc;
+        xMax = x;
       }
     }
 
-    for (var x = 1; x < puzzle.width - 1; x++) {
-      int matchCount = 0;
-
-      for (var y = minY; y <= maxY; y++) {
-        var l = _getPixelGrayscale(puzzle.getPixel(x - 1, y));
-        var r = _getPixelGrayscale(puzzle.getPixel(x + 1, y));
+    return (xMax - xL - 1) / puzzle.width;
+  }
 
-        // find edge
-        if ((r - l).abs() > 50) {
-          matchCount++;
-        }
+  static List<int> _findAlphaBoundingBox(img.Image image) {
+    int xL = image.width, yT = image.height, xR = 0, yB = 0;
+    for (int y = 0; y < image.height; y++) {
+      for (int x = 0; x < image.width; x++) {
+        if (image.getPixel(x, y).a != 255) continue;
+        if (x < xL) xL = x;
+        if (y < yT) yT = y;
+        if (x > xR) xR = x;
+        if (y > yB) yB = y;
       }
+    }
+    return [xL, yT, xR, yB];
+  }
 
-      if ((matchCount / (maxY - minY + 1.0)) > 0.6) {
-        return x / puzzle.width;
+  static double _calculateMean(
+      img.Image image, int x, int y, int width, int height) {
+    double sum = 0;
+    for (int _y = y; _y < y + height; _y++) {
+      for (int _x = x; _x < x + width; _x++) {
+        sum += image.getPixel(_x, _y).luminance;
       }
     }
+    return sum / (width * height);
+  }
 
-    return null;
+  static List<double> _normalizeImage(
+      img.Image image, int x, int y, int width, int height, double mean) {
+    var normalized = List<double>.filled(width * height, 0);
+    for (int _y = 0; _y < height; _y++) {
+      for (int _x = 0; _x < width; _x++) {
+        normalized[_y * width + _x] =
+            image.getPixel(_x + x, _y + y).luminance - mean;
+      }
+    }
+    return normalized;
   }
 
-  static int _getPixelGrayscale(img.Pixel p) {
-    return (0.2126 * p.r + 0.7152 * p.g + 0.0722 * p.b).round();
+  static double _calculateNCC(img.Image window, int x, int y, int width,
+      int height, List<double> template, double meanW) {
+    double sumWt = 0;
+    double sumWw = 0;
+    var iT = template.iterator;
+    for (int _y = y; _y < y + height; _y++) {
+      for (int _x = x; _x < x + width; _x++) {
+        iT.moveNext();
+        double w = window.getPixel(_x, _y).luminance - meanW;
+        sumWt += w * iT.current;
+        sumWw += w * w;
+      }
+    }
+    return sumWt / sumWw;
   }
 }
 

lib/page/setting/about_page/about_page.dart

@@ -83,7 +83,7 @@ class AboutPage extends StatelessWidget {
     Developer(
       "Pairman",
       "https://avatars.githubusercontent.com/u/18365163",
-      "开发：成绩信息缓存功能",
+      "开发：成绩缓存功能和优化滑块算法",
       "https://github.com/Pairman",
     ),
     Developer(