Cleanup: use IMB_FTYPE_NONE instead of 0 for imbuf format comparison

Image format code checked the file type against an enum except for
zero which is used when the format can't be detected.

Also add doc-strings to some of the image file type callbacks.

source/blender/blenkernel/intern/image.c

@@ -1341,7 +1341,7 @@ int BKE_image_imtype_to_ftype(const char imtype, ImbFormatOptions *r_options)
 
 char BKE_image_ftype_to_imtype(const int ftype, const ImbFormatOptions *options)
 {
-  if (ftype == 0) {
+  if (ftype == IMB_FTYPE_NONE) {
     return R_IMF_IMTYPE_TARGA;
   }
   if (ftype == IMB_FTYPE_IMAGIC) {

source/blender/blenkernel/intern/packedFile.c

@@ -536,8 +536,8 @@ static void unpack_generate_paths(const char *name,
       ImagePackedFile *imapf = ((Image *)id)->packedfiles.last;
       if (imapf != NULL && imapf->packedfile != NULL) {
         const PackedFile *pf = imapf->packedfile;
-        const int ftype = IMB_ispic_type_from_memory((const uchar *)pf->data, pf->size);
-        if (ftype != 0) {
+        enum eImbFileType ftype = IMB_ispic_type_from_memory((const uchar *)pf->data, pf->size);
+        if (ftype != IMB_FTYPE_NONE) {
           const int imtype = BKE_image_ftype_to_imtype(ftype, NULL);
           BKE_image_path_ensure_ext_from_imtype(tempname, imtype);
         }

source/blender/imbuf/IMB_imbuf_types.h

@@ -69,7 +69,7 @@ typedef struct DDSData {
  * See T46524. */
 
 /** #ImBuf.ftype flag, main image types. */
-enum eImbTypes {
+enum eImbFileType {
   IMB_FTYPE_PNG = 1,
   IMB_FTYPE_TGA = 2,
   IMB_FTYPE_JPG = 3,
@@ -98,6 +98,9 @@ enum eImbTypes {
 #endif
 };
 
+/* Only for readability. */
+#define IMB_FTYPE_NONE 0
+
 /* ibuf->foptions flag, type specific options.
  * Some formats include compression rations on some bits */
 
@@ -243,7 +246,7 @@ typedef struct ImBuf {
 
   /* file information */
   /** file type we are going to save as */
-  enum eImbTypes ftype;
+  enum eImbFileType ftype;
   /** file format specific flags */
   ImbFormatOptions foptions;
   /** filename associated with this image */

source/blender/imbuf/intern/IMB_filetype.h

@@ -29,15 +29,26 @@ struct ImBuf;
 #define IM_FTYPE_FLOAT 1
 
 typedef struct ImFileType {
+  /** Optional, called once when initializing. */
   void (*init)(void);
+  /** Optional, called once when exiting. */
   void (*exit)(void);
 
+  /**
+   * Check if the data matches this file types 'magic',
+   * \note that this may only read in a small part of the files header,
+   * see: #IMB_ispic_type for details.
+   */
   bool (*is_a)(const unsigned char *buf, const size_t size);
+
+  /** Load an image from memory. */
   struct ImBuf *(*load)(const unsigned char *mem,
                         size_t size,
                         int flags,
                         char colorspace[IM_MAX_SPACE]);
+  /** Load an image from a file. */
   struct ImBuf *(*load_filepath)(const char *filepath, int flags, char colorspace[IM_MAX_SPACE]);
+  /** Save to a file (or memory if #IB_mem is set in `flags` and the format supports it). */
   bool (*save)(struct ImBuf *ibuf, const char *filepath, int flags);
   void (*load_tile)(struct ImBuf *ibuf,
                     const unsigned char *mem,
@@ -47,7 +58,10 @@ typedef struct ImFileType {
                     unsigned int *rect);
 
   int flag;
+
+  /** #eImbFileType */
   int filetype;
+
   int default_save_role;
 } ImFileType;
 

source/blender/imbuf/intern/util.c

@@ -159,7 +159,7 @@ int IMB_ispic_type_from_memory(const unsigned char *buf, const size_t buf_size)
     }
   }
 
-  return 0;
+  return IMB_FTYPE_NONE;
 }
 
 int IMB_ispic_type(const char *filepath)
@@ -167,7 +167,7 @@ int IMB_ispic_type(const char *filepath)
   unsigned char buf[HEADER_SIZE];
   const ssize_t buf_size = imb_ispic_read_header_from_filepath(filepath, buf);
   if (buf_size <= 0) {
-    return 0;
+    return IMB_FTYPE_NONE;
   }
   return IMB_ispic_type_from_memory(buf, (size_t)buf_size);
 }
@@ -196,7 +196,7 @@ bool IMB_ispic_type_matches(const char *filepath, int filetype)
 
 bool IMB_ispic(const char *filepath)
 {
-  return (IMB_ispic_type(filepath) != 0);
+  return (IMB_ispic_type(filepath) != IMB_FTYPE_NONE);
 }
 
 static bool isavi(const char *filepath)

source/blender/makesrna/intern/rna_image.c

@@ -235,7 +235,8 @@ static int rna_Image_file_format_get(PointerRNA *ptr)
 {
   Image *image = (Image *)ptr->data;
   ImBuf *ibuf = BKE_image_acquire_ibuf(image, NULL, NULL);
-  int imtype = BKE_image_ftype_to_imtype(ibuf ? ibuf->ftype : 0, ibuf ? &ibuf->foptions : NULL);
+  int imtype = BKE_image_ftype_to_imtype(ibuf ? ibuf->ftype : IMB_FTYPE_NONE,
+                                         ibuf ? &ibuf->foptions : NULL);
 
   BKE_image_release_ibuf(image, ibuf, NULL);
 

source/blender/windowmanager/intern/wm_playanim.c

@@ -1391,7 +1391,7 @@ static char *wm_main_playanim_intern(int argc, const char **argv)
     while (ps.picture) {
       int hasevent;
 #ifndef USE_IMB_CACHE
-      if (ibuf != NULL && ibuf->ftype == 0) {
+      if (ibuf != NULL && ibuf->ftype == IMB_FTYPE_NONE) {
         IMB_freeImBuf(ibuf);
       }
 #endif