Blame SOURCES/0001-Correctly-read-PNG-into-bitmaps-N32BitTcA.-formats-w.patch

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From 41594786266265c1b7d5116ab85b38af0cd1fd59 Mon Sep 17 00:00:00 2001
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From: Stephan Bergmann <sbergman@redhat.com>
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Date: Wed, 23 Sep 2020 12:01:35 +0200
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Subject: [PATCH] Correctly read PNG into bitmaps N32BitTcA... formats (where
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 alpha comes first)
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This appears to be a regression introduced with
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86ea64f216819696cd86d1926aff0a138ace2baf "Support for native 32bit Bitmap in VCL
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and SVP (cairo) backend".  It caused CppunitTest_vcl_png_test to fail on
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(big-endian) Linux s390x with
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> vcl/qa/cppunit/png/PngFilterTest.cxx:176:PngFilterTest::testPng
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> equality assertion failed
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> - Expected: c[ff000040]
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> - Actual  : c[0000ff40]
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where eFormat happens to be ScanlineFormat::N32BitTcArgb, vs.
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ScanlineFormat::N32BitTcBgra on e.g. Linux x86-64 (and which thus didn't notice
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the lack of support for N32BitTcA... formats where alpha goes first instead of
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last).
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Change-Id: Id6030468718f6ef831b42f2b5ad7ba2c4c46a805
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Reviewed-on: https://gerrit.libreoffice.org/c/core/+/103240
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Tested-by: Jenkins
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Reviewed-by: Stephan Bergmann <sbergman@redhat.com>
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(cherry picked from commit 0387077e6647d7a30fd36d4ec41dfc559afe45c3)
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---
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 vcl/source/filter/png/PngImageReader.cxx | 11 ++++++++++-
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 1 file changed, 10 insertions(+), 1 deletion(-)
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diff --git a/vcl/source/filter/png/PngImageReader.cxx b/vcl/source/filter/png/PngImageReader.cxx
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index 958cae34eb46..6e9f3825face 100644
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--- a/vcl/source/filter/png/PngImageReader.cxx
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+++ b/vcl/source/filter/png/PngImageReader.cxx
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@@ -188,6 +188,8 @@ bool reader(SvStream& rStream, BitmapEx& rBitmapEx, bool bUseBitmap32)
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                     for (auto& rRow : aRows)
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                         rRow.resize(aRowSizeBytes, 0);
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+                    auto const alphaFirst = (eFormat == ScanlineFormat::N32BitTcAbgr
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+                                             || eFormat == ScanlineFormat::N32BitTcArgb);
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                     for (int pass = 0; pass < nNumberOfPasses; pass++)
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                     {
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                         for (png_uint_32 y = 0; y < height; y++)
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@@ -199,10 +201,17 @@ bool reader(SvStream& rStream, BitmapEx& rBitmapEx, bool bUseBitmap32)
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                             for (size_t i = 0; i < aRowSizeBytes; i += 4)
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                             {
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                                 sal_Int8 alpha = pRow[i + 3];
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+                                if (alphaFirst)
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+                                {
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+                                    pScanline[iColor++] = alpha;
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+                                }
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                                 pScanline[iColor++] = vcl::bitmap::premultiply(pRow[i + 0], alpha);
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                                 pScanline[iColor++] = vcl::bitmap::premultiply(pRow[i + 1], alpha);
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                                 pScanline[iColor++] = vcl::bitmap::premultiply(pRow[i + 2], alpha);
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-                                pScanline[iColor++] = alpha;
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+                                if (!alphaFirst)
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+                                {
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+                                    pScanline[iColor++] = alpha;
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+                                }
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                             }
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                         }
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                     }
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-- 
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2.33.1
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