1 files changed, 79 insertions, 0 deletions
diff --git a/gifed/src/block/screendescriptor.rs b/gifed/src/block/screendescriptor.rs
new file mode 100644
index 0000000..dc0257d
--- /dev/null
+++ b/gifed/src/block/screendescriptor.rs
@@ -0,0 +1,79 @@
+use std::convert::TryInto;
+
+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 new(width: u16, height: u16) -> Self {
+		Self {
+			width,
+			height,
+			packed: 0,
+			background_color_index: 0,
+			pixel_aspect_ratio: 0,
+		}
+	}
+
+	pub fn set_color_table_present(&mut self, is_present: bool) {
+		if is_present {
+			self.packed |= 0b1000_0000;
+		} else {
+			self.packed &= 0b0111_1111;
+		}
+	}
+
+	pub fn set_color_table_size(&mut self, size: u8) {
+		println!("scts: {}", size);
+		// 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
+
+	pub fn color_table_present(&self) -> bool {
+		self.packed & 0b1000_0000 != 0
+	}
+
+	pub fn color_table_len(&self) -> usize {
+		crate::packed_to_color_table_length(self.packed & 0b0000_0111)
+	}
+}
+
+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()
+	}
+}
+
+impl From<[u8; 7]> for ScreenDescriptor {
+	fn from(arr: [u8; 7]) -> Self {
+		let width = u16::from_le_bytes(arr[0..2].try_into().unwrap());
+		let height = u16::from_le_bytes(arr[2..4].try_into().unwrap());
+		let packed = arr[4];
+		let background_color_index = arr[5];
+		let pixel_aspect_ratio = arr[6];
+
+		Self {
+			width,
+			height,
+			packed,
+			background_color_index,
+			pixel_aspect_ratio,
+		}
+	}
+}