msvc: disable warning about using setjmp w/c++ objects in scope

Source/Core/VideoCommon/ImageWrite.cpp

@@ -21,6 +21,11 @@ bool SaveData(const std::string& filename, const std::string& data)
   return true;
 }
 
+#ifdef _MSC_VER
+#pragma warning(push)
+#pragma warning(disable : 4611)
+#endif
+
 /*
 TextureToPng
 
@@ -31,20 +36,16 @@ row_stride: Determines the amount of bytes per row of pixels.
 bool TextureToPng(const u8* data, int row_stride, const std::string& filename, int width,
                   int height, bool saveAlpha)
 {
-  bool success = false;
-
   if (!data)
     return false;
 
+  bool success = false;
   char title[] = "Dolphin Screenshot";
   char title_key[] = "Title";
   png_structp png_ptr = nullptr;
   png_infop info_ptr = nullptr;
   std::vector<u8> buffer;
 
-  if (!saveAlpha)
-    buffer.resize(width * 4);
-
   // Open file for writing (binary mode)
   File::IOFile fp(filename, "wb");
   if (!fp.IsOpen())
@@ -70,13 +71,22 @@ bool TextureToPng(const u8* data, int row_stride, const std::string& filename, i
     goto finalise;
   }
 
-  // Setup Exception handling
+  // Classical libpng error handling uses longjmp to do C-style unwind.
+  // Modern libpng does support a user callback, but it's required to operate
+  // in the same way (just gives a chance to do stuff before the longjmp).
+  // Instead of futzing with it, we use gotos specifically so the compiler
+  // will still generate proper destructor calls for us (hopefully).
+  // We also do not use any local variables outside the region longjmp may
+  // have been called from if they were modified inside that region (they
+  // would need to be volatile).
   if (setjmp(png_jmpbuf(png_ptr)))
   {
     PanicAlert("Screenshot failed: Error during PNG creation");
     goto finalise;
   }
 
+  // Begin region which may call longjmp
+
   png_init_io(png_ptr, fp.GetHandle());
 
   // Write header (8 bit color depth)
@@ -91,6 +101,9 @@ bool TextureToPng(const u8* data, int row_stride, const std::string& filename, i
 
   png_write_info(png_ptr, info_ptr);
 
+  if (!saveAlpha)
+    buffer.resize(width * 4);
+
   // Write image data
   for (auto y = 0; y < height; ++y)
   {
@@ -114,6 +127,8 @@ bool TextureToPng(const u8* data, int row_stride, const std::string& filename, i
   // End write
   png_write_end(png_ptr, nullptr);
 
+  // End region which may call longjmp
+
   success = true;
 
 finalise:
@@ -124,3 +139,7 @@ finalise:
 
   return success;
 }
+
+#ifdef _MSC_VER
+#pragma warning(pop)
+#endif