Do not allocate memory to transform layer if image is already set as single-layer

src/engine/image.cpp

@@ -21,7 +21,6 @@
 #include "image.h"
 
 #include <algorithm>
-#include <cassert>
 #include <cmath>
 #include <cstddef>
 #include <cstdlib>
@@ -507,7 +506,11 @@ namespace fheroes2
         if ( !empty() ) {
             const size_t totalSize = static_cast<size_t>( _width ) * _height;
             memset( image(), value, totalSize );
-            memset( transform(), static_cast<uint8_t>( 0 ), totalSize );
+
+            if ( !_singleLayer ) {
+                // For double-layer image: set the transform layer not to skip all data.
+                memset( transform(), static_cast<uint8_t>( 0 ), totalSize );
+            }
         }
     }
 
@@ -523,7 +526,8 @@ namespace fheroes2
             return;
         }
 
-        const size_t size = static_cast<size_t>( width_ ) * height_ * 2;
+        // Allocate memory only for the used layers.
+        const size_t size = static_cast<size_t>( width_ ) * height_ * ( _singleLayer ? 1 : 2 );
 
         _data.reset( new uint8_t[size] );
 
@@ -536,8 +540,11 @@ namespace fheroes2
         if ( !empty() ) {
             const size_t totalSize = static_cast<size_t>( _width ) * _height;
             memset( image(), static_cast<uint8_t>( 0 ), totalSize );
-            // Set the transform layer to skip all data.
-            memset( transform(), static_cast<uint8_t>( 1 ), totalSize );
+
+            if ( !_singleLayer ) {
+                // Set the transform layer to skip all data.
+                memset( transform(), static_cast<uint8_t>( 1 ), totalSize );
+            }
         }
     }
 
@@ -549,7 +556,8 @@ namespace fheroes2
             return;
         }
 
-        const size_t size = static_cast<size_t>( image._width ) * image._height * 2;
+        // Allocate memory and copy data only for the used layers.
+        const size_t size = static_cast<size_t>( image._width ) * image._height * ( _singleLayer ? 1 : 2 );
 
         _singleLayer = image._singleLayer;
 

src/engine/image.h

@@ -19,6 +19,7 @@
  ***************************************************************************/
 #pragma once
 
+#include <cassert>
 #include <cstdint>
 #include <memory>
 #include <utility>
@@ -63,11 +64,17 @@ namespace fheroes2
 
         uint8_t * transform()
         {
+            // Why do you want to get transform layer from the single-layer image?
+            assert( !_singleLayer );
+
             return _data.get() + width() * height();
         }
 
         const uint8_t * transform() const
         {
+            // Why do you want to get transform layer from the single-layer image?
+            assert( !_singleLayer );
+
             return _data.get() + width() * height();
         }
 
@@ -76,15 +83,17 @@ namespace fheroes2
             return !_data;
         }
 
-        void reset(); // makes image fully transparent (transform layer is set to 1)
+        // Set all data in the image layer to 0 and make double-layer images fully transparent (transform layer is set to 1).
+        void reset();
 
-        void clear(); // makes the image empty
+        // Make the image empty.
+        void clear();
 
-        // Fill 'image' layer with given value, setting 'transform' layer to 0.
+        // Fill 'image' layer with given value, setting the double-layer images 'transform' layer to 0.
         void fill( const uint8_t value );
 
-        // This is an optional indicator for image processing functions.
-        // The whole image still consists of 2 layers but transform layer might be ignored in computations
+        // This is an indicator for image processing functions.
+        // The single-layer image can not contain transform layer so this layer is never accessed for such images.
         bool singleLayer() const
         {
             return _singleLayer;