tdf#113918: Workaround: Load 1bpp indexed PNG as 8bpp indexed Bitmap

The alternative, to fix the X11 disaster area used by the gen, gtk,
and kde4 VCL plugins, seemed more difficult. Somebody else with more
time, feel free to revert and do that instead.

Change-Id: I068ea27224ba98be25e01671546137ddd70691a7
Reviewed-on: https://gerrit.libreoffice.org/44957Reviewed-by: Tor Lillqvist <tml@collabora.com>
Tested-by: Tor Lillqvist <tml@collabora.com>

vcl/source/gdi/pngread.cxx

@@ -531,10 +531,19 @@ bool PNGReaderImpl::ImplReadHeader( const Size& rPreviewSizeHint )
         {
             switch ( mnPngDepth )
             {
+                case 1 :
+#if defined(UNX) && !defined(MACOSX)
+                    // 1bpp indexed images are so badly mishandled by rest of LO on X11 that we
+                    // don't even bother, and turn them into 8bpp indexed ones with just two palette
+                    // entries instead.
+                    mnTargetDepth = 8;  // we have to expand the bitmap
+#endif
+                    mbPalette = false;
+                    break;
                 case 2 :
                     mnTargetDepth = 4;  // we have to expand the bitmap
-                    SAL_FALLTHROUGH;
-                case 1 :
+                    mbPalette = false;
+                    break;
                 case 4 :
                 case 8 :
                     mbPalette = false;
@@ -1327,7 +1336,7 @@ void PNGReaderImpl::ImplDrawScanline( sal_uInt32 nXStart, sal_uInt32 nXAdd )
                 }
                 else // neither alpha nor transparency
                 {
-                    if ( mnPngDepth == 8 )  // maybe the source is a 16 bit grayscale
+                    if ( mnPngDepth == 8 )  // maybe the source is a 16 bit grayscale or 1 bit indexed
                     {
                         if( nXAdd == 1 && mnPreviewShift == 0 )  // copy raw line data if possible
                         {
@@ -1342,6 +1351,22 @@ void PNGReaderImpl::ImplDrawScanline( sal_uInt32 nXStart, sal_uInt32 nXAdd )
                                 ImplSetPixel( nY, nX, *pTmp++ );
                         }
                     }
+                    else if (mnPngDepth == 1 )
+                    {
+                        for ( long nX = nXStart, nShift = 0; nX < maOrigSize.Width(); nX += nXAdd )
+                        {
+                            nShift = (nShift - 1) & 7;
+
+                            sal_uInt8 nCol;
+                            if ( nShift == 0 )
+                                nCol = *(pTmp++);
+                            else
+                                nCol = static_cast<sal_uInt8>( *pTmp >> nShift );
+                            nCol &= 1;
+
+                            ImplSetPixel( nY, nX, nCol );
+                        }
+                    }
                     else
                     {
                         for ( long nX = nXStart; nX < maOrigSize.Width(); nX += nXAdd, pTmp += 2 )