From 32dbf71e3a9b103ac98b7c978d53c040bcdc1288 Mon Sep 17 00:00:00 2001
From: marc <marc@lazarus-ide.org>
Date: Tue, 31 Aug 2010 21:32:03 +0000
Subject: [PATCH] * add workaround for alpha channel on palette based PNG
 images for fpc2.4 (fixed in fpc r15926 #af088605bf). Fixes issue #0017267

git-svn-id: trunk@27242 -
---
 lcl/intfgraphics.pas | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/lcl/intfgraphics.pas b/lcl/intfgraphics.pas
index 0c7ccedfc4..36cd0141f0 100644
--- a/lcl/intfgraphics.pas
+++ b/lcl/intfgraphics.pas
@@ -5764,9 +5764,27 @@ begin
 end;
 
 procedure TLazReaderPNG.HandleAlpha;
+{$ifdef VER2_4}
+var
+  n: Integer;
+  c: TFPColor;
+{$endif}
 begin
   inherited HandleAlpha;
   FAlphaPalette := Header.ColorType = 3;
+
+  // check for fpc 2.4, it expands the alpha channel wrong, so the MSByte isn't set
+  {$ifdef VER2_4}
+  if not FAlphaPalette then Exit;
+  for n := 0 to ThePalette.Count - 1 do
+  begin
+    c := ThePalette[n];
+    if c.Alpha and $FF00 <> 0 then Continue;
+    if c.Alpha = 0 then Continue;
+    c.Alpha := c.Alpha shl 8 or c.Alpha;
+    ThePalette[n] := c;
+  end;
+  {$endif}
 end;
 
 procedure TLazReaderPNG.InternalRead(Str: TStream; Img: TFPCustomImage);