tdf#156525 Save as > HTML loses drawing object as invalid gif

regression from
commit 1c7cbd685633d44eac554629572f3401c450f855
Author: Noel Grandin <noel.grandin@collabora.co.uk>
Date:   Sun May 7 16:56:21 2023 +0200
use AlphaMask for variables when calling GetAlphaMask

where after my change, the code is now calling
Bitmap::Replace(AlphaMask,...)
instead of
Bitmap::Replace(Bitmap,...)
and those two methods do quite different things.

However, we have to
(*) restore Bitmap::Replace(Bitmap,...) which was removed in
commit 8270eb5d5600cc84dbf5f0e339f90c4519ef88bb
Author: Noel Grandin <noel.grandin@collabora.co.uk>
Date:   Fri May 19 13:35:31 2023 +0200
loplugin:unusedmethods
(*) restore BitmapWriteAccess::SetPaletteEntryCount which was removed in
commit 74cd0d0b281f8df75612bfb600df2eae62c4d21d
Author: Noel Grandin <noel.grandin@collabora.co.uk>
Date:   Thu Jun 29 13:53:30 2023 +0200
loplugin:unusedmethods
(*) Invert the mask/alpha layer, since after
commit 81994cb2b8b32453a92bcb011830fcb884f22ff3
Author: Noel Grandin <noelgrandin@gmail.com>
Date:   Fri Apr 16 20:33:10 2021 +0200
Convert internal vcl bitmap formats transparency->alpha (II)
we are dealing with real alpha, and not transparency.

Also add an assert in GIFWriter::WriteAccess, since it is a logic error
to get here and have the image in the wrong format.

Change-Id: I0e09b3ca82af0bd5b58d80e0a6eac4c7bdf7c48e
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/155254
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

1 files changed, 75 insertions, 0 deletions

diff --git a/vcl/source/bitmap/bitmappaint.cxx b/vcl/source/bitmap/bitmappaint.cxx
index 487e6d1a6ad6..91a43b951748 100644
--- a/vcl/source/bitmap/bitmappaint.cxx
+++ b/vcl/source/bitmap/bitmappaint.cxx
@@ -884,6 +884,81 @@ vcl::Region Bitmap::CreateRegion(const Color& rColor, const tools::Rectangle& rR
     return aRegion;
 }
 
+bool Bitmap::ReplaceMask(const AlphaMask& rMask, const Color& rReplaceColor)
+{
+    ScopedReadAccess pMaskAcc(const_cast<AlphaMask&>(rMask));
+    BitmapScopedWriteAccess pAcc(*this);
+
+    if (!pMaskAcc || !pAcc)
+        return false;
+
+    const tools::Long nWidth = std::min(pMaskAcc->Width(), pAcc->Width());
+    const tools::Long nHeight = std::min(pMaskAcc->Height(), pAcc->Height());
+    const BitmapColor aMaskWhite(pMaskAcc->GetBestMatchingColor(COL_WHITE));
+    BitmapColor aReplace;
+
+    if (pAcc->HasPalette())
+    {
+        const sal_uInt16 nActColors = pAcc->GetPaletteEntryCount();
+        const sal_uInt16 nMaxColors = 1 << pAcc->GetBitCount();
+
+        // default to the nearest color
+        aReplace = pAcc->GetBestMatchingColor(rReplaceColor);
+
+        // for paletted images without a matching palette entry
+        // look for an unused palette entry (NOTE: expensive!)
+        if (pAcc->GetPaletteColor(aReplace.GetIndex()) != BitmapColor(rReplaceColor))
+        {
+            // if the palette has empty entries use the last one
+            if (nActColors < nMaxColors)
+            {
+                pAcc->SetPaletteEntryCount(nActColors + 1);
+                pAcc->SetPaletteColor(nActColors, rReplaceColor);
+                aReplace = BitmapColor(static_cast<sal_uInt8>(nActColors));
+            }
+            else
+            {
+                std::unique_ptr<bool[]> pFlags(new bool[nMaxColors]);
+
+                // Set all entries to false
+                std::fill(pFlags.get(), pFlags.get() + nMaxColors, false);
+
+                for (tools::Long nY = 0; nY < nHeight; nY++)
+                {
+                    Scanline pScanline = pAcc->GetScanline(nY);
+                    for (tools::Long nX = 0; nX < nWidth; nX++)
+                        pFlags[pAcc->GetIndexFromData(pScanline, nX)] = true;
+                }
+
+                for (sal_uInt16 i = 0; i < nMaxColors; i++)
+                {
+                    // Hurray, we do have an unused entry
+                    if (!pFlags[i])
+                    {
+                        pAcc->SetPaletteColor(i, rReplaceColor);
+                        aReplace = BitmapColor(static_cast<sal_uInt8>(i));
+                    }
+                }
+            }
+        }
+    }
+    else
+        aReplace = rReplaceColor;
+
+    for (tools::Long nY = 0; nY < nHeight; nY++)
+    {
+        Scanline pScanline = pAcc->GetScanline(nY);
+        Scanline pScanlineMask = pMaskAcc->GetScanline(nY);
+        for (tools::Long nX = 0; nX < nWidth; nX++)
+        {
+            if (pMaskAcc->GetPixelFromData(pScanlineMask, nX) == aMaskWhite)
+                pAcc->SetPixelOnData(pScanline, nX, aReplace);
+        }
+    }
+
+    return true;
+}
+
 bool Bitmap::Replace(const AlphaMask& rAlpha, const Color& rMergeColor)
 {
     Bitmap aNewBmp(GetSizePixel(), vcl::PixelFormat::N24_BPP);