Cleanup: Use new OIIO valid_file API

Now that OIIO has proper `valid_file` APIs for the formats we care
about, and which take MemReaders, we can remove the code added to TIFF,
PSD, and PNG as part of 5cc8fea7e9.

Additionally, this change eliminates the recent console spew on startup
where the TIFF loader is asked to load non-TIFF files (it is based on
the ordering of the filetype array)[1]. We now make a `valid_file` check
during open to address this.

[1] `: Not a TIFF or MDI file, bad magic number 12150 (0x2f76).`

Pull Request: https://projects.blender.org/blender/blender/pulls/116826

source/blender/imbuf/intern/format_png.cc

@@ -19,11 +19,7 @@ extern "C" {
 
 bool imb_is_a_png(const uchar *mem, size_t size)
 {
-  const char signature[] = {0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A};
-  if (size < sizeof(signature)) {
-    return false;
-  }
-  return memcmp(signature, mem, sizeof(signature)) == 0;
+  return imb_oiio_check(mem, size, "png");
 }
 
 ImBuf *imb_load_png(const uchar *mem, size_t size, int flags, char colorspace[IM_MAX_SPACE])

source/blender/imbuf/intern/format_psd.cc

@@ -19,11 +19,7 @@ extern "C" {
 
 bool imb_is_a_psd(const uchar *mem, size_t size)
 {
-  const uchar magic[4] = {'8', 'B', 'P', 'S'};
-  if (size < sizeof(magic)) {
-    return false;
-  }
-  return memcmp(magic, mem, sizeof(magic)) == 0;
+  return imb_oiio_check(mem, size, "psd");
 }
 
 ImBuf *imb_load_psd(const uchar *mem, size_t size, int flags, char colorspace[IM_MAX_SPACE])

source/blender/imbuf/intern/format_tiff.cc

@@ -19,15 +19,7 @@ extern "C" {
 
 bool imb_is_a_tiff(const uchar *mem, size_t size)
 {
-  constexpr int MAGIC_SIZE = 4;
-  if (size < MAGIC_SIZE) {
-    return false;
-  }
-
-  const char big_endian[MAGIC_SIZE] = {0x4d, 0x4d, 0x00, 0x2a};
-  const char lil_endian[MAGIC_SIZE] = {0x49, 0x49, 0x2a, 0x00};
-  return ((memcmp(big_endian, mem, MAGIC_SIZE) == 0) ||
-          (memcmp(lil_endian, mem, MAGIC_SIZE) == 0));
+  return imb_oiio_check(mem, size, "tif");
 }
 
 ImBuf *imb_load_tiff(const uchar *mem, size_t size, int flags, char colorspace[IM_MAX_SPACE])

source/blender/imbuf/intern/oiio/openimageio_support.cc

@@ -250,7 +250,7 @@ static unique_ptr<ImageInput> get_oiio_reader(const char *format,
 {
   /* Attempt to create a reader based on the passed in format. */
   unique_ptr<ImageInput> in = ImageInput::create(format);
-  if (!in) {
+  if (!(in && in->valid_file(&mem_reader))) {
     return nullptr;
   }
 
@@ -258,7 +258,7 @@ static unique_ptr<ImageInput> get_oiio_reader(const char *format,
   in->set_ioproxy(&mem_reader);
   bool ok = in->open("", r_newspec, config);
   if (!ok) {
-    in.reset();
+    return nullptr;
   }
 
   return in;
@@ -270,8 +270,8 @@ bool imb_oiio_check(const uchar *mem, size_t mem_size, const char *file_format)
 
   /* This memory proxy must remain alive for the full duration of the read. */
   Filesystem::IOMemReader mem_reader(cspan<uchar>(mem, mem_size));
-  unique_ptr<ImageInput> in = get_oiio_reader(file_format, config, mem_reader, spec);
-  return in ? true : false;
+  unique_ptr<ImageInput> in = ImageInput::create(file_format);
+  return in && in->valid_file(&mem_reader);
 }
 
 ImBuf *imb_oiio_read(const ReadContext &ctx,