From 634d85c89f9c3ce19597fef34c6efdd31909b2a9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Guilherme=20Maranh=C3=A3o?=
 <160272402+refotografia@users.noreply.github.com>
Date: Wed, 15 May 2024 15:58:47 +0100
Subject: [PATCH] Added s-curve contrast option

---
 lib/src/filter/contrast_s_curve.dart | 49 ++++++++++++++++++++++++++++
 1 file changed, 49 insertions(+)
 create mode 100644 lib/src/filter/contrast_s_curve.dart

diff --git a/lib/src/filter/contrast_s_curve.dart b/lib/src/filter/contrast_s_curve.dart
new file mode 100644
index 00000000..b006d8d0
--- /dev/null
+++ b/lib/src/filter/contrast_s_curve.dart
@@ -0,0 +1,49 @@
+import 'dart:math';
+import 'dart:typed_data';
+
+import '../color/channel.dart';
+import '../image/image.dart';
+import '../util/math_util.dart';
+
+num? _lastContrast;
+late Uint8List _contrast;
+
+Image contrast_s(Image src,
+    {required num contrast,
+    Image? mask,
+    Channel maskChannel = Channel.luminance}) {
+  if (contrast == 100.0) {
+    return src;
+  }
+
+  if (contrast != _lastContrast) {
+    _lastContrast = contrast;
+
+        contrast = (contrast / 100.0) - 0.12;
+        _contrast = Uint8List(256);
+    for (var i = 0; i < 256; ++i) {
+      _contrast[i] = (((tan(((i / 127.5) - 1) * contrast) + 1.0) / 2.0) * 255.0)
+          .clamp(0, 255)
+          .toInt();
+    }
+  }
+
+  for (final frame in src.frames) {
+    for (final p in frame) {
+      final msk = mask?.getPixel(p.x, p.y).getChannelNormalized(maskChannel);
+      if (msk == null) {
+        p
+          ..r = _contrast[p.r as int]
+          ..g = _contrast[p.g as int]
+          ..b = _contrast[p.b as int];
+      } else {
+        p
+          ..r = mix(p.r, _contrast[p.r as int], msk)
+          ..g = mix(p.g, _contrast[p.g as int], msk)
+          ..b = mix(p.b, _contrast[p.b as int], msk);
+      }
+    }
+  }
+
+  return src;
+}