From d61aa164c06bd085580d7a4a292bd6b2c7615552 Mon Sep 17 00:00:00 2001
From: Stephen Seo <seo.disparate@gmail.com>
Date: Wed, 25 Aug 2021 14:32:19 +0900
Subject: [PATCH] Impl png output of image

---
 example02_threaded_raytracing/src/main.cpp    |  5 +-
 .../src/rayTracer.cpp                         | 62 +++++++++++++++++++
 .../src/rayTracer.hpp                         |  7 ++-
 3 files changed, 71 insertions(+), 3 deletions(-)

diff --git a/example02_threaded_raytracing/src/main.cpp b/example02_threaded_raytracing/src/main.cpp
index 25a2720..924d7a6 100644
--- a/example02_threaded_raytracing/src/main.cpp
+++ b/example02_threaded_raytracing/src/main.cpp
@@ -133,7 +133,10 @@ int main(int argc, char **argv) {
   auto pixels =
       Ex02::RT::renderColorsWithSpheres(outputWidth, outputHeight, threadCount);
 
-  auto outFilename = pixels.writeToFile(outputFile);
+  //  auto outFilename = pixels.writeToFile(outputFile);
+  //  std::cout << "Rendered image saved to " << outFilename << std::endl;
+
+  auto outFilename = pixels.writeToPNG(outputFile);
   std::cout << "Rendered image saved to " << outFilename << std::endl;
 
   return 0;
diff --git a/example02_threaded_raytracing/src/rayTracer.cpp b/example02_threaded_raytracing/src/rayTracer.cpp
index 8f08da7..57a0de7 100644
--- a/example02_threaded_raytracing/src/rayTracer.cpp
+++ b/example02_threaded_raytracing/src/rayTracer.cpp
@@ -2,8 +2,10 @@
 
 #include <array>
 #include <cmath>
+#include <csetjmp>
 #include <cstdio>
 #include <fstream>
+#include <iostream>
 #include <thread>
 
 #include <glm/ext/matrix_transform.hpp>
@@ -46,6 +48,66 @@ std::string Ex02::RT::Image::writeToFile(const std::string &filename) const {
   return outfilename;
 }
 
+std::string Ex02::RT::Image::writeToPNG(const std::string &filename) const {
+  std::string outfilename = filename + ".png";
+
+  FILE *outfile = fopen(outfilename.c_str(), "wb");
+  if (outfile == nullptr) {
+    return "ERROR";
+  }
+
+  const static auto pngErrorLFn = [](png_structp psp, png_const_charp message) {
+    std::cerr << "WARNING [libpng]: " << message << std::endl;
+  };
+
+  const static auto pngWarnLFn = [](png_structp psp, png_const_charp message) {
+    std::cerr << "ERROR [libpng]: " << message << std::endl;
+  };
+
+  png_structp png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, nullptr,
+                                                pngErrorLFn, pngWarnLFn);
+  if (png_ptr == nullptr) {
+    fclose(outfile);
+    return "ERROR";
+  }
+
+  png_infop info_ptr = png_create_info_struct(png_ptr);
+  if (info_ptr == nullptr) {
+    png_destroy_write_struct(&png_ptr, nullptr);
+    fclose(outfile);
+    return "ERROR";
+  }
+
+  if (setjmp(png_jmpbuf(png_ptr))) {
+    png_destroy_write_struct(&png_ptr, &info_ptr);
+    fclose(outfile);
+    return "ERROR";
+  }
+
+  png_init_io(png_ptr, outfile);
+
+  png_set_IHDR(png_ptr, info_ptr, this->width, this->data.size() / this->width,
+               8, PNG_COLOR_TYPE_RGB, PNG_INTERLACE_NONE,
+               PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);
+
+  png_write_info(png_ptr, info_ptr);
+
+  png_set_filler(png_ptr, 0, PNG_FILLER_AFTER);
+
+  for (unsigned int j = 0; j < this->data.size() / this->width; ++j) {
+    unsigned char *dataPtr =
+        reinterpret_cast<unsigned char *>(&this->data.at(j * this->width));
+    png_write_rows(png_ptr, &dataPtr, 1);
+  }
+
+  png_write_end(png_ptr, nullptr);
+
+  png_destroy_write_struct(&png_ptr, &info_ptr);
+
+  fclose(outfile);
+  return outfilename;
+}
+
 /*
 glm::mat4x4 Ex02::RT::Internal::defaultMVP() {
     glm::mat4x4 mvp = glm::perspective(
diff --git a/example02_threaded_raytracing/src/rayTracer.hpp b/example02_threaded_raytracing/src/rayTracer.hpp
index 1571328..3554608 100644
--- a/example02_threaded_raytracing/src/rayTracer.hpp
+++ b/example02_threaded_raytracing/src/rayTracer.hpp
@@ -18,7 +18,7 @@ constexpr float EX02_RAY_TRACER_GRAY_SPHERE_RADIUS = 1.5F;
 
 namespace Ex02::RT {
 
-struct Pixel {
+struct alignas(4) Pixel {
   Pixel();
 
   unsigned char r, g, b;
@@ -34,9 +34,12 @@ public:
   // returns actual output filename (it appends the file extension)
   std::string writeToFile(const std::string &filename) const;
 
+  // returns actual output filename (it appends the file extension)
+  std::string writeToPNG(const std::string &filename) const;
+
 private:
   unsigned int width;
-  std::vector<Pixel> data;
+  mutable std::vector<Pixel> data;
 };
 
 namespace Internal {