From 1661d5ff48b2f3f4777479faa9fc50fee88965b0 Mon Sep 17 00:00:00 2001
From: wp_xyz <wp_xxyyzzz@gmx.net>
Date: Mon, 30 Jun 2025 17:09:25 +0200
Subject: [PATCH] LCL/Graphics: Fix handling of color transparency in
 TRasterImage and descendants. Issue #41726.

---
 lcl/graphics.pp             |  2 ++
 lcl/include/rasterimage.inc | 24 ++++++++++++++++++------
 2 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/lcl/graphics.pp b/lcl/graphics.pp
index 9d28125358..500cbdf944 100644
--- a/lcl/graphics.pp
+++ b/lcl/graphics.pp
@@ -1245,6 +1245,7 @@ type
     FUpdateCount: Integer;
     FUpdateCanvasOnly: Boolean;
     FMasked: Boolean;
+    FTransparentPending: Boolean;
 
     procedure CanvasChanging(Sender: TObject);
     procedure CreateCanvas;
@@ -1300,6 +1301,7 @@ type
     procedure WriteData(Stream: TStream); override;
     procedure WriteStream(AStream: TMemoryStream); virtual; abstract;
     function  RequestTransparentColor: TColor;
+    procedure ApplyTransparent;
   public
     constructor Create; override;
     destructor Destroy; override;
diff --git a/lcl/include/rasterimage.inc b/lcl/include/rasterimage.inc
index 9ff89bead7..b83fa574ca 100644
--- a/lcl/include/rasterimage.inc
+++ b/lcl/include/rasterimage.inc
@@ -379,9 +379,7 @@ begin
   then FTransparentMode := tmAuto
   else FTransparentMode := tmFixed;
 
-  if MaskHandleAllocated
-  then MaskHandle := 0
-  else Changed(Self);
+  ApplyTransparent;
 end;
 
 procedure TRasterImage.Changed(Sender: TObject);
@@ -702,9 +700,14 @@ begin
   if AValue = TransparentMode then exit;
   FTransparentMode := AValue;
 
-  if AValue = tmAuto
+  if FTransparentColor = clDefault then
+    FTransparentMode := tmAuto;
+
+  if FTransparentMode = tmAuto
   then TransparentColor := clDefault
   else TransparentColor := RequestTransparentColor;
+
+  ApplyTransparent;
 end;
 
 procedure TRasterImage.SetTransparent(AValue: Boolean);
@@ -714,8 +717,8 @@ begin
   lTransparent := GetTransparent();
   if AValue = lTransparent then Exit;
 
-  // some delphi compatibility, we can only change transparency through the mask.
-  Masked := AValue;
+  FTransparentPending := AValue;
+  ApplyTransparent;
 end;
 
 // release handles without freeing them
@@ -976,6 +979,15 @@ begin
   SetSize(Width, AHeight);
 end;
 
+procedure TRasterImage.ApplyTransparent;
+begin
+  if MaskHandleAllocated then
+    MaskHandle := 0;
+
+  // some delphi compatibility, we can only change transparency through the mask.
+  SetMasked(FTransparentPending);
+end;
+
 // included by graphics.pp