Добавлена вторая задача пятой главы

Занимательное программирование/5/2_grey/grey.cpp

@@ -0,0 +1,91 @@
+#include <exception>
+#include "grey.hpp"
+#include <arpa/inet.h>
+
+#define STB_IMAGE_IMPLEMENTATION
+#include "stb_image.h"
+#define STB_IMAGE_WRITE_IMPLEMENTATION
+#include "stb_image_write.h"
+
+static void push_in_network_order(std::uint32_t input, std::vector<std::uint8_t>& output)
+{
+    input = htonl(input);
+    auto pointer_range = reinterpret_cast<std::uint8_t *>(&input);
+    std::copy(pointer_range, pointer_range + 4, std::back_inserter(output));
+}
+
+static std::uint32_t pop_in_native_order(std::string::const_iterator& input)
+{
+    std::uint32_t in_native = ntohl(*reinterpret_cast<const std::uint32_t *>(&*input));
+    input += 4;
+
+    return in_native;
+}
+
+std::vector<std::uint8_t> to_rle(const std::filesystem::path& input)
+{
+    int x, y, n;
+    unsigned char *data = stbi_load(input.native().data(), &x, &y, &n, 1);
+
+    if (data == nullptr)
+    {
+        throw std::runtime_error(stbi_failure_reason());
+    }
+    unsigned char *original_data = data;
+    std::uint8_t current_color = 255;
+    std::uint32_t current_count = 0;
+    std::vector<std::uint8_t> rle_stream;
+
+    push_in_network_order(x, rle_stream);
+    push_in_network_order(y, rle_stream);
+    push_in_network_order(1, rle_stream);
+
+    for (std::size_t i = 0; i < x; ++i)
+    {
+        for (std::size_t j = 0; j < y; ++j)
+        {
+            if (current_color == *data)
+            {
+                ++current_count;
+            }
+            else
+            {
+                current_color = current_color == 255 ? 0 : 255;
+                push_in_network_order(current_count, rle_stream);
+                current_count = 1;
+            }
+            ++data;
+        }
+    }
+    stbi_image_free(original_data);
+    if (current_count != 0)
+    {
+        push_in_network_order(current_count, rle_stream);
+    }
+    return rle_stream;
+}
+
+void from_rle(const std::string& input, const std::filesystem::path& output)
+{
+    std::vector<std::uint8_t> buffer;
+    auto input_position = std::cbegin(input);
+
+    int x = pop_in_native_order(input_position);
+    int y = pop_in_native_order(input_position);
+    int comp = pop_in_native_order(input_position);
+
+    std::uint8_t current_color = 255;
+    std::uint32_t current_count = 0;
+
+    while (input_position != std::cend(input))
+    {
+        auto in_native = pop_in_native_order(input_position);
+
+        for (; in_native > 0; --in_native)
+        {
+            buffer.push_back(current_color);
+        }
+        current_color = current_color == 255 ? 0 : 255;
+    }
+    stbi_write_jpg(output.native().data(), x, y, comp, buffer.data(), 100);
+}