Add Ppm output

tray/src/main.cpp

@@ -1 +1,45 @@
-int main() {}
+#include <array>
+#include <cassert>
+#include <iostream>
+#include <ostream>
+#include <span>
+
+namespace {
+struct Rgb {
+	std::array<std::uint8_t, 3> values{};
+};
+
+struct ImageData {
+	std::span<Rgb const> data{};
+	std::array<std::uint32_t, 2> extent{};
+};
+
+std::ostream& operator<<(std::ostream& out, ImageData const& image) {
+	assert(image.data.size() == image.extent[0] * image.extent[1]);
+	// write header
+	out << "P3\n" << image.extent[0] << ' ' << image.extent[1] << "\n255\n";
+	// write each row
+	for (std::uint32_t row = 0; row < image.extent[1]; ++row) {
+		// write each column
+		for (std::uint32_t col = 0; col < image.extent[0]; ++col) {
+			// compute index
+			auto const index = row * image.extent[0] + col;
+			// obtain corresponding Rgb
+			auto const& rgb = image.data[index];
+			// write out each channel
+			for (auto const channel : rgb.values) { out << static_cast<int>(channel) << ' '; }
+		}
+		out << '\n';
+	}
+	return out;
+}
+} // namespace
+
+int main() {
+	static constexpr auto extent = std::array{40U, 30U};
+	static constexpr auto white_v = Rgb{.values = {0xff, 0xff, 0xff}};
+	auto buffer = std::array<Rgb, extent[0] * extent[1]>{};
+	std::fill_n(buffer.data(), buffer.size(), white_v);
+	auto const image_data = ImageData{.data = buffer, .extent = extent};
+	std::cout << image_data;
+}