initial

obu.odin

@@ -0,0 +1,70 @@
+package avif
+
+import "core:io"
+
+OBUType :: enum u8 {
+    SEQUENCE_HEADER        = 1,
+    TEMPORAL_DELIMITER     = 2,
+    FRAME_HEADER           = 3,
+    TILE_GROUP             = 4,
+    METADATA               = 5,
+    FRAME                  = 6,
+    REDUNDANT_FRAME_HEADER = 7,
+    TILE_LIST              = 8,
+    PADDING                = 15,
+}
+
+// TODO: write a nice bitstream reader
+// ??? Still don't know how I want this to work
+BitstreamReader :: struct {
+    data: []byte,
+    pos: i64, // Number of bits read from the data slice
+}
+
+OBUHeader :: bit_field u8 {
+    obu_reserved:       u8      | 1,
+    obu_has_size_field: u8      | 1,
+    obu_extension_flag: u8      | 1,
+    obu_type:           OBUType | 4,
+    obu_forbidden_bit:  u8      | 1,
+}
+
+OBUExtensionHeader :: bit_field u8 {
+    extension_header_reserved: u8 | 3,
+    spatial_id:                u8 | 2,
+    temporal_id:               u8 | 3,
+}
+
+read_bit :: proc() -> b8 {
+    // TODO: idfk
+    // This should read a single bit from the bitstream and advance the bitstream position by 1
+
+    return false
+}
+
+f :: proc(n: int) -> u64 {
+    x: u64 = 0
+
+    for i in 0 ..< n {
+        x = 2 * x + auto_cast read_bit()
+    }
+
+    return x
+}
+
+leb128 :: proc() -> u64 {
+    value: u64 = 0
+    leb128_bytes := 0
+
+    for i: u64 = 0; i < 8; i += 1 {
+        leb128_byte := f(8)
+        value |= ((leb128_byte & 0x7f) << (i * 7))
+        leb128_bytes += 1
+
+        if (leb128_byte & 0x80) == 0 {
+            break
+        }
+    }
+
+    return value
+}