Implement bitmap and PPM serialization (with a demo program).

3 files changed, 97 insertions, 2 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index a5c54e5..b822baa 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -12,11 +12,12 @@ set(CMAKE_VERBOSE_MAKEFILE on)
 
 # main executable
 
-add_executable(rt main.cpp vec.h)
+add_executable(rt main.cpp vec.h bitmap.h)
+add_executable(image_output main_image_output.cpp vec.h bitmap.h)
 
 # googletest
 
-add_executable(all_tests test.cpp)
+add_executable(all_tests test.cpp vec.h bitmap.h)
 
 target_link_libraries(all_tests gtest_main)
 include(FetchContent)
diff --git a/bitmap.h b/bitmap.h
new file mode 100644
index 0000000..b94bb25
--- /dev/null
+++ b/bitmap.h
@@ -0,0 +1,74 @@
+//
+// Created by Keuin on 2022/4/11.
+//
+
+#ifndef RT_BITMAP_H
+#define RT_BITMAP_H
+
+#include <vector>
+#include <cstdint>
+#include <ostream>
+#include <cassert>
+
+
+// T is some unsigned integer, do not use float point types!
+template<typename T>
+struct pixel {
+    T r, g, b;
+};
+
+// 8 bit pixel
+using pixel8b = pixel<uint8_t>;
+
+template<typename T>
+class bitmap {
+    const unsigned width, height;
+    std::vector<pixel<T>> content; // pixels scanned by rows, from top to bottom
+
+    pixel<T> &image(unsigned x, unsigned y) {
+        assert(x < width);
+        assert(y < height);
+        return content[x * width + y];
+    }
+
+    pixel<T> &image(unsigned x, unsigned y) const {
+        assert(x < width);
+        assert(y < height);
+        return content[x * width + y];
+    }
+
+public:
+    bitmap(unsigned int width, unsigned int height) : width(width), height(height) {
+        content.resize(width * height, pixel<T>{});
+    }
+
+    void set(unsigned x, unsigned y, const pixel<T> &pixel) {
+        image(x, y) = pixel;
+    }
+
+    pixel<T> get(unsigned x, unsigned y) const {
+        return image(x, y);
+    }
+
+    // Do not use float-point pixels, or this routine will break.
+    void write_plain_ppm(std::ostream &out) const;
+};
+
+template<typename T>
+void bitmap<T>::write_plain_ppm(std::ostream &out) const {
+    const auto depth = (1ULL << (sizeof(T) * 8)) - 1ULL; // color depth of pixels
+    out << "P3\n" // file header
+        << width << ' ' << height << '\n' // image width and height
+        << depth << '\n'; // normalized max color depth (e.g. 255 for 8bit image)
+
+    for (const auto &pixel: content) {
+        out << (unsigned long long) pixel.r << ' '
+            << (unsigned long long) pixel.g << ' '
+            << (unsigned long long) pixel.b << '\n';
+    }
+}
+
+using bitmap8b = bitmap<uint8_t>;
+
+
+#endif //RT_BITMAP_H
diff --git a/main_image_output.cpp b/main_image_output.cpp
new file mode 100644
index 0000000..10301da
--- /dev/null
+++ b/main_image_output.cpp
@@ -0,0 +1,20 @@
+//
+// Created by Keuin on 2022/4/11.
+//
+
+#include <iostream>
+#include "bitmap.h"
+
+// write a test .PPM image
+int main() {
+    bitmap8b image{256, 256};
+    pixel8b p{};
+    for (int x = 0; x < 256; ++x) {
+        for (int y = 0; y < 256; ++y) {
+            p.r = x;
+            p.b = y;
+            image.set(x, y, p);
+        }
+    }
+    image.write_plain_ppm(std::cout);
+}
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