patterns/fbx: Improved the FBX pattern (#302)

* patterns/fbx: Improved the FBX pattern
-Added pragma magic
-Fixed sizing of compressed contents array
-Added references
-Cleaned up whitespace

* Added missing ] bracket in README.md

patterns/fbx.hexpat

@@ -1,6 +1,12 @@
 #pragma description Kaydara FBX Binary
+#pragma magic [4B 61 79 64 61 72 61 20 46 42 58 20 42 69 6E 61 72 79 20 20 00 1A 00] @ 0x00
 
-// Based on Blenders implementation of FBX import/export
+/*
+ * Based on Blenders implementation of FBX import/export, see:
+ * (incomplete) https://code.blender.org/2013/08/fbx-binary-file-format-specification/
+ * https://projects.blender.org/blender/blender/src/branch/main/scripts/addons_core/io_scene_fbx/parse_fbx.py
+ * https://projects.blender.org/blender/blender/src/branch/main/scripts/addons_core/io_scene_fbx/encode_bin.py
+ */
 
 #pragma endian little
 
@@ -17,9 +23,9 @@ struct Array<E> {
     u32 arrayLength;
     u32 encoding;
     u32 compressedLength;
-    
+
     std::assert(encoding < 2, "Invalid array encoding!");
-    
+
     if (encoding == 0) {
         // Uncompressed
         E contents[arrayLength];
@@ -31,7 +37,11 @@ struct Array<E> {
         #ifdef __IMHEX__
             std::mem::Section contentsSection = std::mem::create_section(std::format("contentsSection @ {:#x}", pos));
             hex::dec::zlib_decompress(compressedContents, contentsSection, 15);
-            E contents[] @ 0x00 in contentsSection;
+            auto contentsSectionSize = std::mem::get_section_size(contentsSection);
+            auto contentsElementSize = sizeof(E);
+            std::assert_warn((contentsSectionSize % contentsElementSize) == 0,
+                             "The size of the contentsSection must be an integer multiple of sizeof(E) !");
+            E contents[contentsSectionSize / contentsElementSize] @ 0x00 in contentsSection;
         #endif
     }
 };
@@ -57,7 +67,7 @@ enum PropertyTypeCode : char {
 
 struct PropertyRecord {
     PropertyTypeCode typeCode;
-    
+
     match (typeCode) {
         (PropertyTypeCode::BYTE): s8 data;
         (PropertyTypeCode::SHORT): s16 data;
@@ -90,15 +100,15 @@ struct NodeRecord32 {
     u32 numProperties;
     u32 propertyListLen;
     u8 nameLen;
-    
+
     // Detect sentinel record which marks the end of a list of node records
-    if (endOffset == 0 
+    if (endOffset == 0
-        && numProperties == 0 
+        && numProperties == 0
-        && propertyListLen == 0 
+        && propertyListLen == 0
         && nameLen == 0) {
         break;
     }
-    
+
     char name[nameLen];
     auto posBeforePropertyRecords = $;
     auto posAfterPropertyRecords = posBeforePropertyRecords + propertyListLen;
@@ -113,15 +123,15 @@ struct NodeRecord64 {
     u64 numProperties;
     u64 propertyListLen;
     u8 nameLen;
-    
+
     // Detect sentinel record which marks the end of a list of node records
-    if (endOffset == 0 
+    if (endOffset == 0
-        && numProperties == 0 
+        && numProperties == 0
-        && propertyListLen == 0 
+        && propertyListLen == 0
         && nameLen == 0) {
         break;
     }
-    
+
     char name[nameLen];
     auto posBeforePropertyRecords = $;
     auto posAfterPropertyRecords = posBeforePropertyRecords + propertyListLen;
@@ -133,27 +143,27 @@ struct NodeRecord64 {
 
 fn assertZero (auto array, u128 size, auto message) {
     bool nonzeroPadding = false;
-    
+
     for (u8 i = 0, i < size, i = i + 1) {
         if (array[i] != 0) {
             nonzeroPadding = true;
         }
     }
-    
+
     std::assert_warn(!nonzeroPadding, message);
 };
 
-struct Footer{
+struct Footer {
     type::Magic<"\xFA\xBC\xAB\x09\xD0\xC8\xD4\x66\xB1\x76\xFB\x83\x1C\xF7\x26\x7E"> footerId;
     char zeroes[4];
     assertZero(zeroes, 4, "Found non-zero values in footer after footerId!");
     u128 ofs = $;
     u8 alignmentPaddingSize = ((ofs + 15) & ~15) - ofs;
-    
+
     if (alignmentPaddingSize == 0) {
         alignmentPaddingSize = 16;
     }
-    
+
     char alignmentPadding[alignmentPaddingSize];
     assertZero(alignmentPadding, alignmentPaddingSize, "Found non-zero bytes in alignmentPadding!");
     u32 version;
@@ -162,7 +172,6 @@ struct Footer{
     type::Magic<"\xF8\x5A\x8C\x6A\xDE\xF5\xD9\x7E\xEC\xE9\x0C\xE3\x75\x8F\x29\x0B"> footerMagic;
 };
 
-
 struct Header {
     type::Magic<"Kaydara FBX Binary  \x00\x1A\x00"> magic;
     u32 version;
@@ -170,15 +179,15 @@ struct Header {
 
 struct FBX {
     Header header;
-    
+
-    if  (header.version < 7500) {
+    if (header.version < 7500) {
         NodeRecord32 rootRecords[while(true)];
     } else {
         NodeRecord64 rootRecords[while(true)];
     }
-    
+
     Footer footer;
     std::assert_warn(header.version == footer.version, "Version numbers in header and footer do not match!");
 };
 
-FBX fbx @ 0x00;
+FBX fbx @ 0x00;