Refactor: is_exr_file checks memory buffer

All places that used is_exr_file already had first four bytes
of the file read into memory. So make is_exr_file work just
like is_dds_file does and check those bytes directly, no need
to hit stdio again.

renderdoc/common/dds_readwrite.cpp

@@ -952,7 +952,7 @@ RDResult write_dds_to_file(FILE *f, const write_tex_data &data)
   return RDResult();
 }
 
-bool is_dds_file(byte *headerBuffer, size_t size)
+bool is_dds_file(const byte *headerBuffer, size_t size)
 {
   if(size < 4)
   {

renderdoc/common/dds_readwrite.h

@@ -28,6 +28,6 @@
 #include "serialise/streamio.h"
 #include "tex_data.h"
 
-extern bool is_dds_file(byte *headerBuffer, size_t size);
+extern bool is_dds_file(const byte *headerBuffer, size_t size);
 extern RDResult load_dds_from_file(StreamReader *reader, read_tex_data &data);
 extern RDResult write_dds_to_file(FILE *f, const write_tex_data &data);

renderdoc/core/core.h

@@ -42,7 +42,7 @@ struct ReplayOptions;
 struct SDObject;
 
 // not provided by tinyexr, just do by hand
-bool is_exr_file(FILE *f);
+bool is_exr_file(const byte *headerBuffer, size_t size);
 void LogReplayOptions(const ReplayOptions &opts);
 
 enum class RDCDriver : uint32_t;

renderdoc/core/image_viewer.cpp

@@ -433,7 +433,7 @@ RDResult IMG_CreateReplayDevice(RDCFile *rdc, IReplayDriver **driver)
   FileIO::fseek64(f, 0, SEEK_SET);
 
   // make sure the file is a type we recognise before going further
-  if(is_exr_file(f))
+  if(is_exr_file(headerBuffer, headerSize))
   {
     FileIO::fseek64(f, 0, SEEK_END);
     uint64_t size = FileIO::ftell64(f);
@@ -645,7 +645,7 @@ void ImageViewer::RefreshFile()
   uint64_t fileSize = FileIO::ftell64(f);
   FileIO::fseek64(f, 0, SEEK_SET);
 
-  if(is_exr_file(f))
+  if(is_exr_file(headerBuffer, headerSize))
   {
     texDetails.format = rgba32_float;
 

renderdoc/serialise/rdcfile.cpp

@@ -33,18 +33,14 @@
 #include "zstdio.h"
 
 // not provided by tinyexr, just do by hand
-bool is_exr_file(FILE *f)
+bool is_exr_file(const byte *headerBuffer, size_t size)
 {
-  FileIO::fseek64(f, 0, SEEK_SET);
-
+  if(size < 4)
+  {
+    return false;
+  }
   const uint32_t openexr_magic = MAKE_FOURCC(0x76, 0x2f, 0x31, 0x01);
-
-  uint32_t magic = 0;
-  size_t bytesRead = FileIO::fread(&magic, 1, sizeof(magic), f);
-
-  FileIO::fseek64(f, 0, SEEK_SET);
-
-  return bytesRead == sizeof(magic) && magic == openexr_magic;
+  return memcmp(headerBuffer, &openexr_magic, 4) == 0;
 }
 
 /*
@@ -275,10 +271,7 @@ void RDCFile::Open(const rdcstr &path)
     byte headerBuffer[4];
     const size_t headerSize = FileIO::fread(headerBuffer, 1, 4, m_File);
 
-    if(is_dds_file(headerBuffer, headerSize))
-      ret = x = y = comp = 1;
-
-    if(is_exr_file(m_File))
+    if(is_dds_file(headerBuffer, headerSize) || is_exr_file(headerBuffer, headerSize))
       ret = x = y = comp = 1;
 
     FileIO::fseek64(m_File, 0, SEEK_SET);