Implement sf::Image::saveToMemory

https://github.com/SFML/SFML/pull/1669

Co-authored-by: Chris Thrasher <chrisjthrasher@gmail.com>

include/SFML/Graphics/Image.h

@@ -32,6 +32,7 @@
 #include <SFML/Graphics/Color.h>
 #include <SFML/Graphics/Rect.h>
 #include <SFML/Graphics/Types.h>
+#include <SFML/System/Buffer.h>
 #include <SFML/System/InputStream.h>
 #include <SFML/System/Vector2.h>
 #include <stddef.h>
@@ -156,9 +157,30 @@ CSFML_GRAPHICS_API void sfImage_destroy(sfImage* image);
 ///
 /// \return sfTrue if saving was successful
 ///
+/// \see sfImage_saveToMemory
+///
 ////////////////////////////////////////////////////////////
 CSFML_GRAPHICS_API sfBool sfImage_saveToFile(const sfImage* image, const char* filename);
 
+////////////////////////////////////////////////////////////
+/// \brief Save the image to a buffer in memory
+///
+/// The format of the image must be specified.
+/// The supported image formats are bmp, png, tga and jpg.
+/// This function fails if the image is empty, or if
+/// the format was invalid.
+///
+/// \param image  Image object
+/// \param output Buffer to fill with encoded data
+/// \param format Encoding format to use
+///
+/// \return sfTrue if saving was successful
+///
+/// \see sfImage_saveToFile
+///
+////////////////////////////////////////////////////////////
+CSFML_GRAPHICS_API sfBool sfImage_saveToMemory(const sfImage* image, sfBuffer* output, const char* format);
+
 ////////////////////////////////////////////////////////////
 /// \brief Return the size of an image
 ///