From 903929b3ee1fc1a50c83e33fb1fde0b6a72a2380 Mon Sep 17 00:00:00 2001
From: Jan Klass <kissaki@posteo.de>
Date: Wed, 16 Jul 2025 00:25:38 +0200
Subject: [PATCH 1/3] Split off DrawGray method

---
 .../Drawing/Filters/GrayscaleFilter.cs                | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/src/Greenshot.Editor/Drawing/Filters/GrayscaleFilter.cs b/src/Greenshot.Editor/Drawing/Filters/GrayscaleFilter.cs
index 441102980..ab540f4e0 100644
--- a/src/Greenshot.Editor/Drawing/Filters/GrayscaleFilter.cs
+++ b/src/Greenshot.Editor/Drawing/Filters/GrayscaleFilter.cs
@@ -56,6 +56,13 @@ namespace Greenshot.Editor.Drawing.Filters
                 graphics.ExcludeClip(rect);
             }
 
+            DrawGray(graphics, applyBitmap, applyRect);
+
+            graphics.Restore(state);
+        }
+
+        public static void DrawGray(Graphics graphics, Bitmap applyBitmap, NativeRect applyRect)
+        {
             ColorMatrix grayscaleMatrix = new ColorMatrix(new[]
             {
                 new[]
@@ -83,9 +90,7 @@ namespace Greenshot.Editor.Drawing.Filters
             {
                 ia.SetColorMatrix(grayscaleMatrix);
                 graphics.DrawImage(applyBitmap, applyRect, applyRect.X, applyRect.Y, applyRect.Width, applyRect.Height, GraphicsUnit.Pixel, ia);
-            }
-
-            graphics.Restore(state);
+            }
         }
     }
 }
\ No newline at end of file

From 008fbe5faf6397810dfc1a6d2372ca6fd345446b Mon Sep 17 00:00:00 2001
From: Jan Klass <kissaki@posteo.de>
Date: Wed, 16 Jul 2025 00:25:38 +0200
Subject: [PATCH 2/3] Use LINQ Cast

---
 src/Greenshot.Editor/Drawing/DrawableContainerList.cs | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/Greenshot.Editor/Drawing/DrawableContainerList.cs b/src/Greenshot.Editor/Drawing/DrawableContainerList.cs
index ef30c037f..642c4ca05 100644
--- a/src/Greenshot.Editor/Drawing/DrawableContainerList.cs
+++ b/src/Greenshot.Editor/Drawing/DrawableContainerList.cs
@@ -34,6 +34,7 @@ using Greenshot.Base.Interfaces;
 using Greenshot.Base.Interfaces.Drawing;
 using Greenshot.Editor.Configuration;
 using Greenshot.Editor.Drawing.Fields;
+using Greenshot.Editor.Drawing.Filters;
 using Greenshot.Editor.Forms;
 using Greenshot.Editor.Memento;
 
@@ -328,9 +329,10 @@ namespace Greenshot.Editor.Drawing
                 return;
             }
 
-            foreach (var drawableContainer in this)
+            var drawableContainers = this.Cast<DrawableContainer>();
+
+            foreach (var dc in drawableContainers)
             {
-                var dc = (DrawableContainer) drawableContainer;
                 if (dc.Parent == null)
                 {
                     continue;

From c4a531697483ec905a7d68c917ef9ef7beecbec1 Mon Sep 17 00:00:00 2001
From: Jan Klass <kissaki@posteo.de>
Date: Wed, 16 Jul 2025 18:05:00 +0200
Subject: [PATCH 3/3] Combine multiple grayscale highlights

---
 .../Drawing/DrawableContainer.cs              |  4 ++-
 .../Drawing/DrawableContainerList.cs          | 26 +++++++++++++++++++
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/src/Greenshot.Editor/Drawing/DrawableContainer.cs b/src/Greenshot.Editor/Drawing/DrawableContainer.cs
index cac23dc3a..bed1d7618 100644
--- a/src/Greenshot.Editor/Drawing/DrawableContainer.cs
+++ b/src/Greenshot.Editor/Drawing/DrawableContainer.cs
@@ -410,7 +410,9 @@ namespace Greenshot.Editor.Drawing
                 {
                     if (clipRectangle.Width != 0 && clipRectangle.Height != 0)
                     {
-                        foreach (IFilter filter in Filters)
+                        // GrayscaleFilter is an inverted filter. Combining two makes the entire image greyscale.
+                        // Skip any GrayscaleFilter here so outer drawing logic can handle them to combine multiple
+                        foreach (IFilter filter in Filters.Where(x => x is not GrayscaleFilter))
                         {
                             if (filter.Invert)
                             {
diff --git a/src/Greenshot.Editor/Drawing/DrawableContainerList.cs b/src/Greenshot.Editor/Drawing/DrawableContainerList.cs
index 642c4ca05..a3027808e 100644
--- a/src/Greenshot.Editor/Drawing/DrawableContainerList.cs
+++ b/src/Greenshot.Editor/Drawing/DrawableContainerList.cs
@@ -331,6 +331,8 @@ namespace Greenshot.Editor.Drawing
 
             var drawableContainers = this.Cast<DrawableContainer>();
 
+            ApplyGrayscaleFilters(g, drawableContainers, bitmap);
+
             foreach (var dc in drawableContainers)
             {
                 if (dc.Parent == null)
@@ -343,6 +345,30 @@ namespace Greenshot.Editor.Drawing
                     dc.DrawContent(g, bitmap, renderMode, clipRectangle);
                 }
             }
+
+            // To support multiple grayscale filters we merge them before applying them
+            static void ApplyGrayscaleFilters(Graphics g, IEnumerable<DrawableContainer> drawableContainers, Bitmap bitmap)
+            {
+                if (bitmap is null) return;
+
+                var grayFilters = drawableContainers.SelectMany(x => x.Filters.Where(filter => filter is GrayscaleFilter).Cast<GrayscaleFilter>());
+                // These rects shall not be grayed out
+                var rects = grayFilters.Select(x => x.Parent.Bounds);
+
+                // full bitmap size because the GrayscaleFilter is an inverted filter covering the full bitmap
+                var applyRect = new NativeRect(0, 0, bitmap.Width, bitmap.Height);
+
+                GraphicsState state = g.Save();
+                // Set a clipping region and then exclude the highlight areas so only "everything else" gets greyed out
+                g.SetClip(applyRect);
+                foreach (var rect in rects)
+                {
+                    g.ExcludeClip(rect);
+                }
+                GrayscaleFilter.DrawGray(g, bitmap, applyRect);
+
+                g.Restore(state);
+            }
         }
 
         /// <summary>