Add compress and image to core.

core/image/common.odin

@@ -0,0 +1,107 @@
+package image
+
+import "core:bytes"
+
+Image :: struct {
+	width:      int,
+	height:     int,
+	channels:   int,
+	depth:      u8,
+	pixels:     bytes.Buffer,
+	/*
+		Some image loaders/writers can return/take an optional background color.
+		For convenience, we return them as u16 so we don't need to switch on the type
+		in our viewer, and can just test against nil.
+	*/
+	background: Maybe([3]u16),
+	sidecar:    any,
+}
+
+/*
+Image_Option:
+	`.info`
+		This option behaves as `return_ihdr` and `do_not_decompress_image` and can be used
+		to gather an image's dimensions and color information.
+
+	`.return_header`
+		Fill out img.sidecar.header with the image's format-specific header struct.
+		If we only care about the image specs, we can set `return_header` +
+		`do_not_decompress_image`, or `.info`, which works as if both of these were set.
+
+	`.return_metadata`
+		Returns all chunks not needed to decode the data.
+		It also returns the header as if `.return_header` is set.
+
+	`do_not_decompress_image`
+		Skip decompressing IDAT chunk, defiltering and the rest.
+
+	`alpha_add_if_missing`
+		If the image has no alpha channel, it'll add one set to max(type).
+		Turns RGB into RGBA and Gray into Gray+Alpha
+
+	`alpha_drop_if_present`
+		If the image has an alpha channel, drop it.
+		You may want to use `alpha_premultiply` in this case.
+
+        NOTE: For PNG, this also skips handling of the tRNS chunk, if present,
+        unless you select `alpha_premultiply`.
+        In this case it'll premultiply the specified pixels in question only,
+        as the others are implicitly fully opaque.	
+
+	`alpha_premultiply`
+		If the image has an alpha channel, returns image data as follows:
+			RGB  *= A, Gray = Gray *= A
+
+	`blend_background`
+		If a bKGD chunk is present in a PNG, we normally just set `img.background`
+		with its value and leave it up to the application to decide how to display the image,
+		as per the PNG specification.
+
+		With `blend_background` selected, we blend the image against the background
+		color. As this negates the use for an alpha channel, we'll drop it _unless_
+		you also specify `alpha_add_if_missing`.
+
+	Options that don't apply to an image format will be ignored by their loader.
+*/
+
+Option :: enum {
+	info = 0,
+	do_not_decompress_image,
+	return_header,
+	return_metadata,
+	alpha_add_if_missing,
+	alpha_drop_if_present,
+	alpha_premultiply,
+	blend_background,
+}
+Options :: distinct bit_set[Option];
+
+PNG_Error :: enum {
+	Invalid_PNG_Signature,
+	IHDR_Not_First_Chunk,
+	IHDR_Corrupt,
+	IDAT_Missing,
+	IDAT_Must_Be_Contiguous,
+	IDAT_Corrupt,
+	PNG_Does_Not_Adhere_to_Spec,
+	PLTE_Encountered_Unexpectedly,
+	PLTE_Invalid_Length,
+	TRNS_Encountered_Unexpectedly,
+	BKGD_Invalid_Length,
+	Invalid_Image_Dimensions,
+	Unknown_Color_Type,
+	Invalid_Color_Bit_Depth_Combo,
+	Unknown_Filter_Method,
+	Unknown_Interlace_Method,
+}
+
+
+/*
+	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;
+}