2 files changed, 95 insertions, 0 deletions
diff --git a/src/block/extension/graphiccontrol.rs b/src/block/extension/graphiccontrol.rs
new file mode 100644
index 0000000..46f44fa
--- /dev/null
+++ b/src/block/extension/graphiccontrol.rs
@@ -0,0 +1,59 @@
+pub struct GraphicControl {
+	pub(crate) packed: u8,
+	pub(crate) delay_time: u16,
+	pub(crate) transparency_index: u8
+}
+
+impl GraphicControl {
+	pub fn new(disposal_method: DisposalMethod, user_input_flag: bool, transparency_flag: bool, delay_time: u16, transparency_index: u8) -> Self {
+		let mut ret = Self {
+			packed: 0,
+			delay_time,
+			transparency_index
+		};
+
+		ret.disposal_method(disposal_method);
+		ret.user_input(user_input_flag);
+		ret.transparency(transparency_flag);
+
+		ret
+	}
+
+	pub fn disposal_method(&mut self, method: DisposalMethod) {
+		match method {
+			DisposalMethod::Clear => self.packed &= 0b111_000_1_1,
+			DisposalMethod::DoNotDispose => self.packed |= 0b000_100_0_0,
+			DisposalMethod::RestoreBackground => self.packed |= 0b000_010_0_0,
+			DisposalMethod::RestorePrevious => self.packed |= 0b000_110_0_0
+		};
+	}
+
+	pub fn user_input(&mut self, flag: bool) {
+		if flag {
+			self.packed |= 0b000_000_1_0;
+		} else {
+			self.packed &= 0b111_111_0_1;
+		}
+	}
+
+	pub fn transparency(&mut self, flag: bool) {
+		if flag {
+			self.packed |= 0b000_000_0_1;
+		} else {
+			self.packed &= 0b111_111_1_0;
+		}
+	}
+
+	pub fn delay_time(&mut self, hundreths: u16) {
+		self.delay_time = hundreths;
+	}
+
+	//TODO: Transparency index setter
+}
+
+pub enum DisposalMethod {
+	Clear,
+	DoNotDispose,
+	RestoreBackground,
+	RestorePrevious
+}
\ No newline at end of file
diff --git a/src/block/extension/mod.rs b/src/block/extension/mod.rs
new file mode 100644
index 0000000..4d65c09
--- /dev/null
+++ b/src/block/extension/mod.rs
@@ -0,0 +1,36 @@
+mod graphiccontrol;
+
+pub use graphiccontrol::{DisposalMethod, GraphicControl};
+
+pub enum Extension {
+	GraphicControl(GraphicControl),
+	Looping(u16)
+}
+
+impl From<&Extension> for Box<[u8]> {
+	fn from(ext: &Extension) -> Self {
+		let mut vec = vec![];
+		vec.push(0x21); // Push the extension introducer
+
+		match ext {
+			Extension::GraphicControl(gc) => {
+				vec.push(0xF9); // Graphic control label
+				vec.push(0x04); // Block size for this extension is always 4
+				vec.push(gc.packed);
+				vec.extend_from_slice(&gc.delay_time.to_le_bytes());
+				vec.push(gc.transparency_index);
+			},
+			Extension::Looping(count) => {
+				vec.push(0xFF); // Application extension label
+				vec.push(0x0B); // 11 bytes in this block
+				vec.extend_from_slice(b"NETSCAPE2.0"); // App. ident. and "auth code"
+				vec.push(0x03); // Sub-block length
+				vec.push(0x01); // Identifies netscape looping extension
+				vec.extend_from_slice(&count.to_le_bytes());
+			} 
+		}
+
+		vec.push(0x00); // Zero-length data block indicates end of extension
+		vec.into_boxed_slice()
+	}
+}
\ No newline at end of file