7 files changed, 234 insertions, 0 deletions
diff --git a/src/block/block.rs b/src/block/block.rs
new file mode 100644
index 0000000..95ff12e
--- /dev/null
+++ b/src/block/block.rs
@@ -0,0 +1,9 @@
+use crate::block::Version;
+
+use super::ScreenDescriptor;
+
+
+pub enum Block {
+	Version(Version),
+	LogicalScreenDescriptor(ScreenDescriptor)
+}
\ No newline at end of file
diff --git a/src/block/colortable.rs b/src/block/colortable.rs
new file mode 100644
index 0000000..97b428f
--- /dev/null
+++ b/src/block/colortable.rs
@@ -0,0 +1,67 @@
+use std::ops::Deref;
+pub use crate::Color;
+
+pub struct ColorTable {
+	table: Vec<Color>
+}
+
+impl ColorTable {
+	pub fn new() -> Self {
+		Self {
+			table: vec![]
+		}
+	}
+
+	/// Returns the number of colors in the color table as used by the packed
+	/// fields in the Logical Screen Descriptor and Image Descriptor. You can
+	/// get the actual size with the [`len`](struct.ColorTable.html#method.len) method.
+	pub fn packed_len(&self) -> u8 {
+		((self.table.len() as f32).log2().ceil() - 1f32) as u8
+	}
+
+	/// Returns the number of items in the table
+	pub fn len(&self) -> usize {
+		self.table.len()
+	}
+
+	/// Pushes a color on to the end of the table
+	pub fn push(&mut self, color: Color) {
+		self.table.push(color);
+	}
+}
+
+impl Deref for ColorTable {
+	type Target = [Color];
+
+	fn deref(&self) -> &Self::Target {
+		&self.table
+	}
+}
+
+impl From<Vec<Color>> for ColorTable {
+	fn from(table: Vec<Color>) -> Self{
+		ColorTable {
+			table
+		}
+	}
+}
+
+impl From<&ColorTable> for Box<[u8]> {
+	fn from(table: &ColorTable) -> Self {
+		let mut vec = vec![];
+
+		for color in table.iter() {
+			vec.extend_from_slice(&[color.r, color.g, color.b]);
+		}
+
+		let packed_len = 2u8.pow(table.packed_len() as u32 + 1);
+		let padding = (packed_len as usize - table.len()) * 3;
+		if padding > 0 {
+			vec.extend_from_slice(&vec![0; padding]);
+		}
+
+		vec.into_boxed_slice()
+	}
+}
+
+//TODO: TryFrom Vec<u8> (must be multiple of 3 len) and From Vec<Color>
\ No newline at end of file
diff --git a/src/block/image.rs b/src/block/image.rs
new file mode 100644
index 0000000..07f9555
--- /dev/null
+++ b/src/block/image.rs
@@ -0,0 +1,47 @@
+use crate::LZW;
+use super::{ColorTable, ImageDescriptor};
+
+pub struct Image {
+	pub image_descriptor: ImageDescriptor,
+	pub local_color_table: Option<ColorTable>,
+	pub indicies: Vec<u8>
+}
+
+impl Image {
+	pub fn as_boxed_slice(&self, minimum_code_size: u8) -> Box<[u8]> {
+		let mut out = vec![];
+
+		let mut boxed: Box<[u8]> = (&self.image_descriptor).into();
+		out.extend_from_slice(&*boxed);
+
+		// Table based image data //
+
+		// Get the mcs while we write out the color table
+		let mut mcs = if let Some(lct) = &self.local_color_table {
+			boxed = lct.into();
+			out.extend_from_slice(&*boxed);
+
+			lct.packed_len()
+		} else {
+			minimum_code_size
+		};
+
+		if mcs < 2 {
+			mcs = 2; // Must be true: 0 <= mcs <= 8
+		}
+
+		// First write out the MCS
+		out.push(mcs);
+
+		let compressed = LZW::encode(mcs, &self.indicies);
+		
+		for chunk in compressed.chunks(255) {
+			out.push(chunk.len() as u8);
+			out.extend_from_slice(chunk);
+		}
+		// Data block length 0 to indicate an end
+		out.push(0x00);
+
+		out.into_boxed_slice()
+	}
+}
\ No newline at end of file
diff --git a/src/block/imagedescriptor.rs b/src/block/imagedescriptor.rs
new file mode 100644
index 0000000..c911baa
--- /dev/null
+++ b/src/block/imagedescriptor.rs
@@ -0,0 +1,45 @@
+pub struct ImageDescriptor {
+	// Image Seperator 0x2C is the first byte //
+	pub left: u16,
+	pub top: u16,
+	pub width: u16,
+	pub height: u16,
+	pub packed: u8
+}
+
+impl ImageDescriptor {
+	pub fn color_table_present(&mut self, is_present: bool) {
+		if is_present {
+			self.packed |= 0b1000_0000;
+		} else {
+			self.packed &= 0b0111_1111;
+		}
+	}
+
+	pub fn color_table_size(&mut self, size: u8) {
+		// GCT size is calulated by raising two to this number plus one,
+		// so we have to work backwards.
+		let size = (size as f32).log2().ceil() - 1f32;
+		self.packed |= size as u8;
+	}
+
+	//TODO: Setter for sort flag in packed field
+	//TODO: Setter for interlace flag in packed field
+}
+
+impl From<&ImageDescriptor> for Box<[u8]> {
+	fn from(desc: &ImageDescriptor) -> Self {
+		let mut vec = vec![];
+
+		vec.push(0x2C); // Image Seperator
+		vec.extend_from_slice(&desc.left.to_le_bytes());
+		vec.extend_from_slice(&desc.top.to_le_bytes());
+		vec.extend_from_slice(&desc.width.to_le_bytes());
+		vec.extend_from_slice(&desc.height.to_le_bytes());
+		vec.push(desc.packed);
+
+		vec.into_boxed_slice()
+	}
+}
+
+//TODO: Impl to allow changing the packed field easier
\ No newline at end of file
diff --git a/src/block/mod.rs b/src/block/mod.rs
new file mode 100644
index 0000000..049b39a
--- /dev/null
+++ b/src/block/mod.rs
@@ -0,0 +1,13 @@
+mod block;
+mod colortable;
+mod image;
+mod imagedescriptor;
+mod screendescriptor;
+mod version;
+
+pub use block::Block;
+pub use colortable::ColorTable;
+pub use image::Image;
+pub use imagedescriptor::ImageDescriptor;
+pub use screendescriptor::ScreenDescriptor;
+pub use version::Version;
\ No newline at end of file
diff --git a/src/block/screendescriptor.rs b/src/block/screendescriptor.rs
new file mode 100644
index 0000000..d53d252
--- /dev/null
+++ b/src/block/screendescriptor.rs
@@ -0,0 +1,40 @@
+pub struct ScreenDescriptor {
+	pub width: u16,
+	pub height: u16,
+	pub packed: u8,
+	pub background_color_index: u8,
+	pub pixel_aspect_ratio: u8
+}
+
+impl ScreenDescriptor {
+	pub fn color_table_present(&mut self, is_present: bool) {
+		if is_present {
+			self.packed |= 0b1000_0000;
+		} else {
+			self.packed &= 0b0111_1111;
+		}
+	}
+
+	pub fn color_table_size(&mut self, size: u8) {
+		// GCT size is calulated by raising two to this number plus one,
+		// so we have to work backwards.
+		let size = (size as f32).log2().ceil() - 1f32;
+		self.packed |= size as u8;
+	}
+
+	//TODO: Setter for sort flag in packed field
+	//TODO: Setter for color resolution in packed field
+}
+
+impl From<&ScreenDescriptor> for Box<[u8]> {
+	fn from(lsd: &ScreenDescriptor) -> Self {
+		let mut vec = vec![];
+		vec.extend_from_slice(&lsd.width.to_le_bytes());
+		vec.extend_from_slice(&lsd.height.to_le_bytes());
+		vec.push(lsd.packed);
+		vec.push(lsd.background_color_index);
+		vec.push(lsd.pixel_aspect_ratio);
+
+		vec.into_boxed_slice()
+	}
+}
\ No newline at end of file
diff --git a/src/block/version.rs b/src/block/version.rs
new file mode 100644
index 0000000..a5d688d
--- /dev/null
+++ b/src/block/version.rs
@@ -0,0 +1,13 @@
+pub enum Version {
+	Gif87a,
+	Gif89a
+}
+
+impl From<&Version> for &[u8] {
+	fn from(version: &Version) -> Self {
+		match version {
+			Version::Gif87a => b"GIF87a",
+			Version::Gif89a => b"GIF89a"
+		}
+	}
+}
\ No newline at end of file