Add `image.which` file format testing procedures

core/image/which.odin

@@ -0,0 +1,150 @@
+package image
+
+import "core:os"
+
+Which_File_Type :: enum {
+	Unknown,
+
+	BMP,
+	EXR,
+	GIF,
+	HDR, // Radiance RGBE HDR
+	JPEG,
+	PBM, PGM, PPM, // NetPBM family
+	PIC, // Softimage PIC
+	PNG,
+	PSD, // Photoshop PSD
+	QOI,
+	SGI_RGB, // Silicon Graphics Image RGB file format
+	Sun_Rast, // Sun Raster Graphic
+	TGA, // Targa Truevision
+	TIFF,
+	WebP,
+	XBM, // X BitMap
+}
+
+which :: proc{
+	which_bytes,
+	which_file,
+}
+
+which_bytes :: proc(data: []byte) -> Which_File_Type {
+	test_tga :: proc(s: string) -> bool {
+		get8 :: #force_inline proc(s: ^string) -> u8 {
+			v := s[0]
+			s^ = s[1:]
+			return v
+		}
+		get16le :: #force_inline  proc(s: ^string) -> u16 {
+			v := u16(s[0]) | u16(s[1])<<16
+			s^ = s[2:]
+			return v
+		}
+		s := s
+		s = s[1:] // skip offset
+
+		color_type := get8(&s)
+		if color_type > 1 {
+			return false
+		}
+		image_type := get8(&s) // image type
+		if color_type == 1 { // Colormap (Paletted) Image
+			if image_type != 1 && image_type != 9 { // color type requires 1 or 9
+				return false
+			}
+			s = s[4:] // skip index of first colormap
+			bpcme := get8(&s) // check bits per colormap entry
+			if bpcme != 8 && bpcme != 15 && bpcme != 16 && bpcme != 24 && bpcme != 32 {
+				return false
+			}
+			s = s[4:] // skip image origin (x, y)
+		} else { // Normal image without colormap
+			if image_type != 2 && image_type != 3 && image_type != 10 && image_type != 11 {
+				return false
+			}
+			s = s[9:] // skip colormap specification
+		}
+		if get16le(&s) < 1 || get16le(&s) < 1 { // test width and height
+			return false
+		}
+		bpp := get8(&s) // bits per pixel
+		if color_type == 1 && bpp != 8 && bpp != 16 {
+			return false
+		}
+		if bpp != 8 && bpp != 15 && bpp != 16 && bpp != 24 && bpp != 32 {
+			return false
+		}
+		return true
+	}
+
+	header: [128]byte
+	copy(header[:], data)
+	s := string(header[:])
+
+	switch {
+	case s[:2] == "BM":
+		return .BMP
+	case s[:4] == "\x76\x2f\x31\x01":
+		return .EXR
+	case s[:6] == "GIF87a", s[:6] == "GIF89a":
+		return .GIF
+	case s[6:10] == "JFIF", s[6:10] == "Exif":
+		return .JPEG
+	case s[:4] == "\xff\xd8\xff\xdb":
+		return .JPEG
+	case s[0] == 'P':
+		switch s[2] {
+		case '\t', '\n', '\r':
+			switch s[1] {
+			case '1', '4':
+				return .PBM
+			case '2', '5':
+				return .PGM
+			case '3', '6':
+				return .PPM
+			}
+		}
+	case s[:8] == "\x89PNG\r\n\x1a\n":
+		return .PNG
+	case s[:4] == "qoif":
+		return .QOI
+	case s[:2] == "\x01\xda":
+		return .SGI_RGB
+	case s[:4] == "\x59\xA6\x6A\x95":
+		return .Sun_Rast
+	case s[:2] == "MM", s[:2] == "II":
+		return .TIFF
+	case s[:4] == "RIFF" && s[8:12] == "WEBP":
+		return .WebP
+	case s[:8] == "#define ":
+		return .XBM
+
+	case s[:11] == "#?RADIANCE\n", s[:7] == "#?RGBE\n":
+		return .HDR
+	case s[:4] == "\x38\x42\x50\x53":
+		return .PSD
+	case s[:4] != "\x53\x80\xF6\x34" && s[88:92] == "PICT":
+		return .PIC
+	case:
+		// More complex formats
+		if test_tga(s) {
+			return .TGA
+		}
+
+
+	}
+	return .Unknown
+}
+
+
+which_file :: proc(path: string) -> Which_File_Type {
+	f, err := os.open(path)
+	if err != 0 {
+		return .Unknown
+	}
+	header: [128]byte
+	os.read(f, header[:])
+	file_type := which_bytes(header[:])
+	os.close(f)
+	return file_type
+}