From c44d5f06fcea7af11d03f62a2670030c65ad0089 Mon Sep 17 00:00:00 2001
From: Andreas Grois <andi@grois.info>
Date: Sat, 10 Mar 2018 12:52:52 +0100
Subject: Make sure png file gets closed by wrapping the file descriptor into a
 class with destructor

---
 BuddhaTest/include/Helpers.h | 13 +++++++++++++
 BuddhaTest/src/Helpers.cpp   | 35 ++++++++++++++++++++++++++++-------
 2 files changed, 41 insertions(+), 7 deletions(-)

diff --git a/BuddhaTest/include/Helpers.h b/BuddhaTest/include/Helpers.h
index c24e2c7..ad14305 100644
--- a/BuddhaTest/include/Helpers.h
+++ b/BuddhaTest/include/Helpers.h
@@ -2,6 +2,7 @@
 #include <glad/glad.h>
 #include <GLFW/glfw3.h>
 #include <vector>
+#include <stdio.h> //includes FILE typedef
 
 namespace Helpers
 {
@@ -9,4 +10,16 @@ namespace Helpers
 	GLuint LoadComputeShader(const char * compute_file_path);
 
     void WriteOutputPNG(const std::vector<uint32_t>& data, unsigned int width, unsigned int height);
+
+    /** Wraps around a C file descriptor. Libpng could be taught to use C++ streams, but I'm too lazy and rather wrap this ugly thing up, so it gets cleaned... */
+    class ScopedCFileDescriptor
+    {
+    public:
+        ScopedCFileDescriptor(const char *path, const char *mode);
+        ~ScopedCFileDescriptor();
+        FILE * Get() const;
+        bool IsValid() const;
+    private:
+        FILE * Descriptor;
+    };
 }
diff --git a/BuddhaTest/src/Helpers.cpp b/BuddhaTest/src/Helpers.cpp
index cf925be..fb362ab 100644
--- a/BuddhaTest/src/Helpers.cpp
+++ b/BuddhaTest/src/Helpers.cpp
@@ -2,6 +2,7 @@
 #include <string>
 #include <fstream>
 #include <sstream>
+#include <iostream>
 #include <vector>
 #include <png.h>
 
@@ -147,6 +148,7 @@ namespace Helpers
 		glDeleteShader(ComputeShaderID);
 		return ProgramID;
 	}
+
     void WriteOutputPNG(const std::vector<uint32_t>& data, unsigned int width, unsigned int height)
     {
         png_byte ** row_pointers = static_cast<png_byte **>(calloc(height,sizeof(void *)));
@@ -175,32 +177,29 @@ namespace Helpers
             }
         }
 
-        //beware, this is going to be ugly C syntax, but well, libpng...
-        FILE * fp = fopen("image.png", "wb");
-        if(!fp)
+        ScopedCFileDescriptor fd("image.png", "wb");
+        if(!fd.IsValid())
         {
+            std::cout << "Failed to open image.png for writing." << std::endl;
             return;
         }
         png_structp png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, nullptr, nullptr, nullptr);
         if(!png_ptr)
         {
-            fclose(fp);
             return;
         }
         png_infop info_ptr = png_create_info_struct(png_ptr);
         if(!info_ptr)
         {
             png_destroy_write_struct(&png_ptr, (png_infopp)NULL);
-            fclose(fp);
             return;
         }
         if(setjmp(png_jmpbuf(png_ptr)))
         {
             png_destroy_write_struct(&png_ptr, &info_ptr);
-            fclose(fp);
             return;
         }
-        png_init_io(png_ptr, fp);
+        png_init_io(png_ptr, fd.Get());
         png_set_IHDR(png_ptr, info_ptr, width, height, 8, PNG_COLOR_TYPE_RGB, PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);
 
         png_write_info(png_ptr, info_ptr);
@@ -218,4 +217,26 @@ namespace Helpers
 
         free(row_pointers);
     }
+
+    ScopedCFileDescriptor::ScopedCFileDescriptor(const char *path, const char *mode)
+    {
+        Descriptor = fopen(path,mode);
+    }
+
+    ScopedCFileDescriptor::~ScopedCFileDescriptor()
+    {
+        if(IsValid())
+            fclose(Descriptor);
+    }
+
+    FILE * ScopedCFileDescriptor::Get() const
+    {
+        return Descriptor;
+    }
+
+    bool ScopedCFileDescriptor::IsValid() const
+    {
+        return Descriptor != nullptr;
+    }
+
 }
-- 
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