Add constBits methods to QgsRasterBlock

These can avoid an unwanted QImage detach when we are just
reading block data and don't need to modify it

python/PyQt6/core/auto_generated/raster/qgsrasterblock.sip.in

@@ -352,6 +352,8 @@ overwrite data somewhere in the middle of the internal buffer.
 
 
 
+
+
     static QString printValue( double value );
 %Docstring
 Print double value with all necessary significant digits.

python/core/auto_generated/raster/qgsrasterblock.sip.in

@@ -352,6 +352,8 @@ overwrite data somewhere in the middle of the internal buffer.
 
 
 
+
+
     static QString printValue( double value );
 %Docstring
 Print double value with all necessary significant digits.

src/core/raster/qgsrasterblock.cpp

@@ -506,9 +506,35 @@ char *QgsRasterBlock::bits( qgssize index )
   {
     return reinterpret_cast< char * >( mData ) + index * mTypeSize;
   }
-  if ( mImage && mImage->bits() )
+  if ( mImage )
   {
-    return reinterpret_cast< char * >( mImage->bits() + index * 4 );
+    if ( uchar *data = mImage->bits() )
+    {
+      return reinterpret_cast< char * >( data + index * 4 );
+    }
+  }
+
+  return nullptr;
+}
+
+const char *QgsRasterBlock::constBits( qgssize index ) const
+{
+  // Not testing type to avoid too much overhead because this method is called per pixel
+  if ( index >= static_cast< qgssize >( mWidth )*mHeight )
+  {
+    QgsDebugMsgLevel( QStringLiteral( "Index %1 out of range (%2 x %3)" ).arg( index ).arg( mWidth ).arg( mHeight ), 4 );
+    return nullptr;
+  }
+  if ( mData )
+  {
+    return reinterpret_cast< const char * >( mData ) + index * mTypeSize;
+  }
+  if ( mImage )
+  {
+    if ( const uchar *data = mImage->constBits() )
+    {
+      return reinterpret_cast< const char * >( data + index * 4 );
+    }
   }
 
   return nullptr;
@@ -525,9 +551,29 @@ char *QgsRasterBlock::bits()
   {
     return reinterpret_cast< char * >( mData );
   }
-  if ( mImage && mImage->bits() )
+  if ( mImage )
   {
-    return reinterpret_cast< char * >( mImage->bits() );
+    if ( uchar *data = mImage->bits() )
+    {
+      return reinterpret_cast< char * >( data );
+    }
+  }
+
+  return nullptr;
+}
+
+const char *QgsRasterBlock::constBits() const
+{
+  if ( mData )
+  {
+    return reinterpret_cast< const char * >( mData );
+  }
+  if ( mImage )
+  {
+    if ( const uchar *data = mImage->constBits() )
+    {
+      return reinterpret_cast< const char * >( data );
+    }
   }
 
   return nullptr;

src/core/raster/qgsrasterblock.h

@@ -552,15 +552,39 @@ class CORE_EXPORT QgsRasterBlock
      * Returns a pointer to block data.
      * \param index data matrix index (long type in Python)
      * \note not available in Python bindings
+     *
+     * \see constBits()
      */
     char *bits( qgssize index ) SIP_SKIP;
 
     /**
      * Returns a pointer to block data.
      * \note not available in Python bindings
+     *
+     * \see constBits()
      */
     char *bits() SIP_SKIP;
 
+    /**
+     * Returns a const pointer to block data.
+     *
+     * \param index data matrix index (long type in Python)
+     * \note not available in Python bindings
+     *
+     * \see bits()
+     * \since QGIS 3.38
+     */
+    const char *constBits( qgssize index ) const SIP_SKIP;
+
+    /**
+     * Returns a const pointer to block data.
+     * \note not available in Python bindings
+     *
+     * \see bits()
+     * \since QGIS 3.38
+     */
+    const char *constBits() const SIP_SKIP;
+
     /**
      * \brief Print double value with all necessary significant digits.
      *         It is ensured that conversion back to double gives the same number.

src/core/raster/qgsrasterdataprovider.cpp

@@ -197,7 +197,7 @@ QgsRasterBlock *QgsRasterDataProvider::block( int bandNo, QgsRectangle  const &b
         const qgssize tmpIndex = static_cast< qgssize >( tmpRow ) * static_cast< qgssize >( tmpWidth ) + tmpCol;
         const qgssize index = row * static_cast< qgssize >( width ) + col;
 
-        char *tmpBits = tmpBlock->bits( tmpIndex );
+        const char *tmpBits = tmpBlock->constBits( tmpIndex );
         char *bits = block->bits( index );
         if ( !tmpBits )
         {

src/core/raster/qgsrasterfilewriter.cpp

@@ -529,7 +529,7 @@ Qgis::RasterFileWriterResult QgsRasterFileWriter::writeDataRaster( const QgsRast
         if ( destBlockList[ i - 1 ]->isEmpty() )
           continue;
 
-        if ( !partDestProvider->write( destBlockList[i - 1]->bits( 0 ), i, iterCols, iterRows, 0, 0 ) )
+        if ( !partDestProvider->write( destBlockList[i - 1]->constBits( 0 ), i, iterCols, iterRows, 0, 0 ) )
         {
           return Qgis::RasterFileWriterResult::WriteError;
         }
@@ -545,7 +545,7 @@ Qgis::RasterFileWriterResult QgsRasterFileWriter::writeDataRaster( const QgsRast
         if ( destBlockList[ i - 1 ]->isEmpty() )
           continue;
 
-        if ( !destProvider->write( destBlockList[i - 1]->bits( 0 ), i, iterCols, iterRows, iterLeft, iterTop ) )
+        if ( !destProvider->write( destBlockList[i - 1]->constBits( 0 ), i, iterCols, iterRows, iterLeft, iterTop ) )
         {
           return Qgis::RasterFileWriterResult::WriteError;
         }

src/core/raster/qgsrasterprojector.cpp

@@ -901,8 +901,8 @@ QgsRasterBlock *QgsRasterProjector::block( int bandNo, QgsRectangle  const &exte
       }
 
       const qgssize destIndex = static_cast< qgssize >( i ) * width + j;
-      char *srcBits = inputBlock->bits( srcIndex );
+      const char *srcBits = inputBlock->constBits( srcIndex );
-      char *destBits = outputBlock->bits( destIndex );
+      char *destBits = output->bits( destIndex );
       if ( !srcBits )
       {
         // QgsDebugError( QStringLiteral( "Cannot get input block data: row = %1 col = %2" ).arg( i ).arg( j ) );