prefer 8bit bitmap masks to 1bpp masks

It's much simpler and more performant to work with 8bpp bytes
rather than fiddle with 1bpp bits, and the memory savings don't
really matter nowadays. E.g. the soft edges feature performs
much worse when operating on 1bpp bitmaps (tdf#134237).
I've looked and it seems nothing in LO code actually requires
bitmap masks to really be 1bpp. As a next step we could perhaps
also leave antiquity and embrace the past by dropping 1bpp masks
entirely and using just alpha masks.
The change also moves the workaround for #i75531, it was breaking
CppunitTest_vcl_svm_test and X11-related hacks belong to the X11
code (especially with the X11 backend becoming more and more niche).

Change-Id: I7848f06c8b83bbad2ea35f17f2b65855f8d1f456
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/97839
Tested-by: Jenkins
Reviewed-by: Tomaž Vajngerl <quikee@gmail.com>
Reviewed-by: Luboš Luňák <l.lunak@collabora.com>

4 files changed, 42 insertions, 14 deletions

diff --git a/canvas/source/directx/dx_vcltools.cxx b/canvas/source/directx/dx_vcltools.cxx
index d88c586c3245..287ed7beda54 100644
--- a/canvas/source/directx/dx_vcltools.cxx
+++ b/canvas/source/directx/dx_vcltools.cxx
@@ -168,9 +168,9 @@ namespace dxcanvas
                                   "::dxcanvas::tools::bitmapFromVCLBitmapEx(): "
                                   "Unable to acquire read access to bitmap" );
 
-                if( rBmpEx.IsAlpha() )
+                if( rBmpEx.IsAlpha() || rBmpEx.GetMask().GetBitCount() == 8 )
                 {
-                    Bitmap aAlpha( rBmpEx.GetAlpha().GetBitmap() );
+                    Bitmap aAlpha( rBmpEx.IsAlpha() ? rBmpEx.GetAlpha().GetBitmap() : rBmpEx.GetMask());
 
                     Bitmap::ScopedReadAccess pAlphaReadAccess( aAlpha );
 
diff --git a/vcl/source/bitmap/bitmappaint.cxx b/vcl/source/bitmap/bitmappaint.cxx
index 046b0e3ba3b5..0f4c929480f9 100644
--- a/vcl/source/bitmap/bitmappaint.cxx
+++ b/vcl/source/bitmap/bitmappaint.cxx
@@ -367,6 +367,12 @@ Bitmap Bitmap::CreateMask(const Color& rTransColor, sal_uInt8 nTol) const
 {
     ScopedReadAccess pReadAcc(const_cast<Bitmap&>(*this));
 
+    // Historically LO used 1bpp masks, but 8bpp masks are much faster,
+    // better supported by hardware, and the memory savings are not worth
+    // it anymore.
+    // TODO: Possibly remove the 1bpp code later.
+    constexpr bool use8BitMask = true;
+
     if (!nTol && pReadAcc
         && (pReadAcc->GetScanlineFormat() == ScanlineFormat::N1BitLsbPal
             || pReadAcc->GetScanlineFormat() == ScanlineFormat::N1BitMsbPal)
@@ -377,7 +383,8 @@ Bitmap Bitmap::CreateMask(const Color& rTransColor, sal_uInt8 nTol) const
         return *this;
     }
 
-    Bitmap aNewBmp(GetSizePixel(), 1);
+    Bitmap aNewBmp(GetSizePixel(), use8BitMask ? 8 : 1,
+                   use8BitMask ? &Bitmap::GetGreyPalette(256) : nullptr);
     BitmapScopedWriteAccess pWriteAcc(aNewBmp);
     bool bRet = false;
 
@@ -392,8 +399,9 @@ Bitmap Bitmap::CreateMask(const Color& rTransColor, sal_uInt8 nTol) const
         {
             const BitmapColor aTest(pReadAcc->GetBestMatchingColor(rTransColor));
 
-            if (pReadAcc->GetScanlineFormat() == ScanlineFormat::N4BitMsnPal
-                || pReadAcc->GetScanlineFormat() == ScanlineFormat::N4BitLsnPal)
+            if (pWriteAcc->GetBitCount() == 1
+                && (pReadAcc->GetScanlineFormat() == ScanlineFormat::N4BitMsnPal
+                    || pReadAcc->GetScanlineFormat() == ScanlineFormat::N4BitLsnPal))
             {
                 // optimized for 4Bit-MSN/LSN source palette
                 const sal_uInt8 cTest = aTest.GetIndex();
@@ -433,7 +441,8 @@ Bitmap Bitmap::CreateMask(const Color& rTransColor, sal_uInt8 nTol) const
                     }
                 }
             }
-            else if (pReadAcc->GetScanlineFormat() == ScanlineFormat::N8BitPal)
+            else if (pWriteAcc->GetBitCount() == 1
+                     && pReadAcc->GetScanlineFormat() == ScanlineFormat::N8BitPal)
             {
                 // optimized for 8Bit source palette
                 const sal_uInt8 cTest = aTest.GetIndex();
@@ -486,6 +495,25 @@ Bitmap Bitmap::CreateMask(const Color& rTransColor, sal_uInt8 nTol) const
                         pDst[nX] = ~pSrc[nX];
                 }
             }
+            else if (use8BitMask && pWriteAcc->GetBitCount() == 8
+                     && pReadAcc->GetScanlineFormat() == ScanlineFormat::N8BitPal)
+            {
+                // optimized for 8Bit source palette
+                const sal_uInt8 cTest = aTest.GetIndex();
+
+                for (long nY = 0; nY < nHeight; ++nY)
+                {
+                    Scanline pSrc = pReadAcc->GetScanline(nY);
+                    Scanline pDst = pWriteAcc->GetScanline(nY);
+                    for (long nX = 0; nX < nWidth; ++nX)
+                    {
+                        if (cTest == pSrc[nX])
+                            pDst[nX] = aWhite.GetIndex();
+                        else
+                            pDst[nX] = aBlack.GetIndex();
+                    }
+                }
+            }
             else
             {
                 // not optimized
diff --git a/vcl/source/gdi/bitmapex.cxx b/vcl/source/gdi/bitmapex.cxx
index 80c6879af00c..3f65117392a5 100644
--- a/vcl/source/gdi/bitmapex.cxx
+++ b/vcl/source/gdi/bitmapex.cxx
@@ -126,8 +126,9 @@ BitmapEx::BitmapEx( const Bitmap& rBmp, const Bitmap& rMask ) :
         meTransparent    ( !rMask ? TransparentType::NONE : TransparentType::Bitmap ),
         mbAlpha          ( false )
 {
-    // Ensure a mask is exactly one bit deep
-    if( !!maMask && maMask.GetBitCount() != 1 )
+    // Ensure a mask is exactly one bit deep,
+    // alternatively also allow 8bpp masks.
+    if( !!maMask && maMask.GetBitCount() != 1 && !(maMask.GetBitCount() == 8 && maMask.HasGreyPalette8Bit()))
     {
         SAL_WARN( "vcl", "BitmapEx: forced mask to monochrome");
         BitmapEx aMaskEx(maMask);
@@ -154,12 +155,6 @@ BitmapEx::BitmapEx( const Bitmap& rBmp, const AlphaMask& rAlphaMask ) :
         OSL_ENSURE(false, "Alpha size differs from Bitmap size, corrected Mask (!)");
         maMask.Scale(rBmp.GetSizePixel());
     }
-
-    // #i75531# the workaround below can go when
-    // X11SalGraphics::drawAlphaBitmap()'s render acceleration
-    // can handle the bitmap depth mismatch directly
-    if( maBitmap.GetBitCount() < maMask.GetBitCount() )
-        maBitmap.Convert( BmpConversion::N24Bit );
 }
 
 BitmapEx::BitmapEx( const Bitmap& rBmp, const Color& rTransparentColor ) :
diff --git a/vcl/unx/generic/gdi/gdiimpl.cxx b/vcl/unx/generic/gdi/gdiimpl.cxx
index ee45815a7c83..6310b6ba99fa 100644
--- a/vcl/unx/generic/gdi/gdiimpl.cxx
+++ b/vcl/unx/generic/gdi/gdiimpl.cxx
@@ -714,6 +714,11 @@ bool X11SalGraphicsImpl::drawAlphaBitmap( const SalTwoRect& rTR,
     // non 8-bit alpha not implemented yet
     if( rAlphaBmp.GetBitCount() != 8 )
         return false;
+    // #i75531# the workaround below can go when
+    // X11SalGraphics::drawAlphaBitmap()'s render acceleration
+    // can handle the bitmap depth mismatch directly
+    if( rSrcBitmap.GetBitCount() < rAlphaBmp.GetBitCount() )
+        return false;
 
     // horizontal mirroring not implemented yet
     if( rTR.mnDestWidth < 0 )