patterns: Added PNG Pattern (#27)

* starting to flesh out a pattern for PNG

* using defines to improve readability

* data type changes to wip png pattern

* read png chunks until end of file

* iccp chunk and commenting

* Move IHDR out of array

* Function and pointer fixes

Co-authored-by: Foster Brereton <fbrereto@adobe.com>

README.md

@@ -25,6 +25,7 @@ Hex patterns, include patterns and magic files for the use with the ImHex Hex Ed
 | Java Class | `application/x-java-applet` | `patterns/java_class.hexpat` | Java Class files | 
 | ARM VTOR | | `patterns/arm_cm_vtor.hexpat` | ARM Cortex M Vector Table Layout | 
 | ICO | | `patterns/ico.hexpat` | Icon (.ico) or Cursor (.cur) files | 
+| PNG  | `image/png` | `patterns/png.hexpat` | PNG image files | 
 
 ### Scripts
 

patterns/png.hexpat

@@ -0,0 +1,86 @@
+#pragma MIME image/png
+#pragma endian big
+
+struct header_t
+{
+    u8 highBitByte;
+	char signature[3];
+	char dosLineEnding[2];
+	char dosEOF;
+	char unixLineEnding;
+};
+
+struct ihdr_t
+{
+    u32 width [[comment("Image width")]];
+    u32 height [[comment("Image height")]];
+    u8 bit_depth;
+    u8 color_type [[comment("PNG Image Type\n0: greyscale\n2: truecolour\n3: indexed-color\n4: greyscale with alpha\n6: truecolour with alpha")]];
+    u8 compression_method;
+    u8 filter_method;
+    u8 interlace_method [[comment("values 0 \"no interlace\" or 1 \"Adam7 interlace\"")]];
+};
+
+struct palette_entry_t {
+    u8 r;
+    u8 g;
+    u8 b;
+};
+
+struct phys_t {
+    u32 ppu_x [[comment("Pixels per unit, X axis")]];
+    u32 ppu_y [[comment("Pixels per unit, Y axis")]];
+    u8 unit [[comment("Unit Specifier\n0: unit is unknown\n1: unit is the metre")]];
+};
+
+struct itxt_t {
+    char keyword[];
+    u8 compression_flag;
+    u8 compression_method;
+    char language_tag[];
+    char translated_keyword[];
+    char text[parent.length - ($ - addressof(keyword))];
+};
+
+struct iccp_t {
+	char profile [];
+	u8 compression_method;
+	u8 compressed_profile[parent.length - ($ - addressof(profile))];
+};
+
+struct chunk_t {
+    u32 length [[color("17BECF")]];
+    char type[4];
+
+    #define IHDR_k "IHDR"
+    #define PLTE_k "PLTE"
+    #define pHYs_k "pHYs"
+    #define iTXt_k "iTXt"
+    #define IDAT_k "IDAT"
+    #define IEND_k "IEND"
+    #define gAMA_k "gAMA"
+    #define iCCP_k "iCCP"
+
+    if (type == IHDR_k) {
+        ihdr_t ihdr [[comment("Image Header chunk"), name("IHDR")]];
+    } else if (type == PLTE_k) {
+        palette_entry_t entries[length / 3];
+    } else if (type == pHYs_k) {
+        phys_t phys;
+    } else if (type == iTXt_k) {
+        itxt_t text;
+    } else if (type == gAMA_k) {
+    	u32 gamma [[name("image gamma"), comment("4 byte unsigned integer representing gamma times 100000")]];
+    } else if (type == iCCP_k) {
+    	iccp_t iccp;
+    } else {
+        u8 data[length];
+    }
+
+    u32 crc;
+};
+
+header_t header @ 0x00 [[comment("PNG file signature"), name("Signature")]];
+chunk_t ihdr_chunk @ 0x08 [[comment("PNG Header chunk"), name("IHDR")]];
+chunk_t chunk_set[while(builtin::std::mem::read_string($ + 4, 4) != "IEND")] @ $ [[comment("PNG file chunks"), name("Chunks"), inline]];
+chunk_t iend_chunk @ $ [[name("IEND"), comment("Image End Chunk")]];