Add SaveImageResource implementation for libpng

olcPixelGameEngine.h

@@ -4255,6 +4255,102 @@ namespace olc
 
 		olc::rcode SaveImageResource(const olc::Sprite* spr, const std::string& sImageFile) override
 		{
+			if (spr == nullptr)
+				return olc::rcode::FAIL;
+
+			// RAII wrapper for FILE pointer
+			struct FileWrapper
+			{
+				FILE* f = nullptr;
+
+				FileWrapper(const std::string& sImageFile)
+				{
+					f = fopen(sImageFile.c_str(), "wb");
+				}
+
+				FileWrapper(const FileWrapper&) = delete;
+				FileWrapper(FileWrapper&&) = delete;
+				FileWrapper& operator=(const FileWrapper&) = delete;
+				FileWrapper& operator=(FileWrapper&&) = delete;
+
+				~FileWrapper()
+				{
+					if (f != nullptr)
+						fclose(f);
+				}
+
+				bool Good() const
+				{
+					return f != nullptr;
+				}
+			};
+
+			// RAII wrapper for png_struct and png_info pointers
+			struct PNGStructWrapper
+			{
+				struct PNGError
+				{};
+
+				png_structp png_ptr = nullptr;
+				png_infop info_ptr = nullptr;
+
+				PNGStructWrapper()
+				{
+					png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, PNGStructWrapper::user_error_handling_func, PNGStructWrapper::user_warn_func);
+					if (png_ptr != nullptr)
+						info_ptr = png_create_info_struct(png_ptr);
+				}
+
+				PNGStructWrapper(const PNGStructWrapper&) = delete;
+				PNGStructWrapper(PNGStructWrapper&&) = delete;
+				PNGStructWrapper& operator=(const PNGStructWrapper&) = delete;
+				PNGStructWrapper& operator=(PNGStructWrapper&&) = delete;
+
+				~PNGStructWrapper()
+				{
+					png_destroy_write_struct(&png_ptr, &info_ptr);
+				}
+
+				bool Good() const
+				{
+					return png_ptr != nullptr && info_ptr != nullptr;
+				}
+
+				static void user_error_handling_func(png_structp, png_const_charp error_msg) {
+					fprintf(stderr, "%s\n", error_msg);
+					throw PNGError{}; // Function must not return control to caller
+				}
+				static void user_warn_func(png_structp, png_const_charp warning_msg) {
+					fprintf(stderr, "%s\n", warning_msg);
+				}
+			};
+
+			try
+			{
+				FileWrapper file(sImageFile);
+				if (!file.Good())
+				{
+					return olc::rcode::FAIL;
+				}
+				PNGStructWrapper png;
+				if (!png.Good())
+				{
+					return olc::rcode::FAIL;
+				}
+				png_init_io(png.png_ptr, file.f);
+				png_set_IHDR(png.png_ptr, png.info_ptr, spr->width, spr->height, 8, PNG_COLOR_TYPE_RGB_ALPHA, PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);
+				std::unique_ptr<png_bytep[]> png_rows = std::make_unique<png_bytep[]>(spr->height);
+				for (int y = 0; y < spr->height; y++)
+					png_rows[y] = (png_bytep)(spr->pColData.data() + std::ptrdiff_t(y) * spr->width);
+
+				png_set_rows(png.png_ptr, png.info_ptr, png_rows.get());
+				png_write_png(png.png_ptr, png.info_ptr, PNG_TRANSFORM_IDENTITY, NULL);
+			}
+			catch (PNGStructWrapper::PNGError&)
+			{
+				return olc::rcode::FAIL;
+			}
+
 			return olc::rcode::OK;
 		}
 	};