png: Move metadata.

core/image/common.odin

@@ -26,8 +26,11 @@ Image :: struct {
 	*/
 	background:    Maybe([3]u16),
 
-	metadata_ptr:  rawptr,
-	metadata_type: typeid,
+	metadata:      Image_Metadata,
+}
+
+Image_Metadata :: union {
+	^PNG_Info,
 }
 
 /*
@@ -152,10 +155,101 @@ PNG_Error :: enum {
 	Invalid_Chunk_Length,
 }
 
+/*
+	PNG-specific structs
+*/
+PNG_Info :: struct {
+	header: PNG_IHDR,
+	chunks: [dynamic]PNG_Chunk,
+}
+
+PNG_Chunk_Header :: struct #packed {
+	length: u32be,
+	type:   PNG_Chunk_Type,
+}
+
+PNG_Chunk :: struct #packed {
+	header: PNG_Chunk_Header,
+	data:   []byte,
+	crc:    u32be,
+}
+
+PNG_Chunk_Type :: enum u32be {
+	// IHDR must come first in a file
+	IHDR = 'I' << 24 | 'H' << 16 | 'D' << 8 | 'R',
+	// PLTE must precede the first IDAT chunk
+	PLTE = 'P' << 24 | 'L' << 16 | 'T' << 8 | 'E',
+	bKGD = 'b' << 24 | 'K' << 16 | 'G' << 8 | 'D',
+	tRNS = 't' << 24 | 'R' << 16 | 'N' << 8 | 'S',
+	IDAT = 'I' << 24 | 'D' << 16 | 'A' << 8 | 'T',
+
+	iTXt = 'i' << 24 | 'T' << 16 | 'X' << 8 | 't',
+	tEXt = 't' << 24 | 'E' << 16 | 'X' << 8 | 't',
+	zTXt = 'z' << 24 | 'T' << 16 | 'X' << 8 | 't',
+
+	iCCP = 'i' << 24 | 'C' << 16 | 'C' << 8 | 'P',
+	pHYs = 'p' << 24 | 'H' << 16 | 'Y' << 8 | 's',
+	gAMA = 'g' << 24 | 'A' << 16 | 'M' << 8 | 'A',
+	tIME = 't' << 24 | 'I' << 16 | 'M' << 8 | 'E',
+
+	sPLT = 's' << 24 | 'P' << 16 | 'L' << 8 | 'T',
+	sRGB = 's' << 24 | 'R' << 16 | 'G' << 8 | 'B',
+	hIST = 'h' << 24 | 'I' << 16 | 'S' << 8 | 'T',
+	cHRM = 'c' << 24 | 'H' << 16 | 'R' << 8 | 'M',
+	sBIT = 's' << 24 | 'B' << 16 | 'I' << 8 | 'T',
+
+	/*
+		eXIf tags are not part of the core spec, but have been ratified
+		in v1.5.0 of the PNG Ext register.
+
+		We will provide unprocessed chunks to the caller if `.return_metadata` is set.
+		Applications are free to implement an Exif decoder.
+	*/
+	eXIf = 'e' << 24 | 'X' << 16 | 'I' << 8 | 'f',
+
+	// PNG files must end with IEND
+	IEND = 'I' << 24 | 'E' << 16 | 'N' << 8 | 'D',
+
+	/*
+		XCode sometimes produces "PNG" files that don't adhere to the PNG spec.
+		We recognize them only in order to avoid doing further work on them.
+
+		Some tools like PNG Defry may be able to repair them, but we're not
+		going to reward Apple for producing proprietary broken files purporting
+		to be PNGs by supporting them.
+
+	*/
+	iDOT = 'i' << 24 | 'D' << 16 | 'O' << 8 | 'T',
+	CbGI = 'C' << 24 | 'b' << 16 | 'H' << 8 | 'I',
+}
+
+PNG_IHDR :: struct #packed {
+	width:              u32be,
+	height:             u32be,
+	bit_depth:          u8,
+	color_type:         PNG_Color_Type,
+	compression_method: u8,
+	filter_method:      u8,
+	interlace_method:   PNG_Interlace_Method,
+}
+PNG_IHDR_SIZE :: size_of(PNG_IHDR)
+#assert (PNG_IHDR_SIZE == 13)
+
+PNG_Color_Value :: enum u8 {
+	Paletted = 0, // 1 << 0 = 1
+	Color    = 1, // 1 << 1 = 2
+	Alpha    = 2, // 1 << 2 = 4
+}
+PNG_Color_Type :: distinct bit_set[PNG_Color_Value; u8]
+
+PNG_Interlace_Method :: enum u8 {
+	None  = 0,
+	Adam7 = 1,
+}
+
 /*
 	Functions to help with image buffer calculations
 */
-
 compute_buffer_size :: proc(width, height, channels, depth: int, extra_row_bytes := int(0)) -> (size: int) {
 	size = ((((channels * width * depth) + 7) >> 3) + extra_row_bytes) * height
 	return
@@ -164,7 +258,6 @@ compute_buffer_size :: proc(width, height, channels, depth: int, extra_row_bytes
 /*
 	For when you have an RGB(A) image, but want a particular channel.
 */
-
 Channel :: enum u8 {
 	R = 1,
 	G = 2,
@@ -226,8 +319,8 @@ return_single_channel :: proc(img: ^Image, channel: Channel) -> (res: ^Image, ok
 	res.depth         = img.depth
 	res.pixels        = t
 	res.background    = img.background
-	res.metadata_ptr  = img.metadata_ptr
-	res.metadata_type = img.metadata_type
+	// res.metadata_ptr  = img.metadata_ptr
+	// res.metadata_type = img.metadata_type
 
 	return res, true
 }