1 files changed, 196 insertions, 0 deletions
diff --git a/src/writer/imagebuilder.rs b/src/writer/imagebuilder.rs
new file mode 100644
index 0000000..cd96908
--- /dev/null
+++ b/src/writer/imagebuilder.rs
@@ -0,0 +1,196 @@
+use crate::common::Color;
+use super::OutVec;
+use super::LZW;
+
+pub struct ImageBuilder {
+	left_offset: u16,
+	top_offset: u16,
+	width: u16,
+	height: u16,
+	color_table: Option<Vec<Color>>,
+	indicies: Vec<u8>
+}
+
+impl ImageBuilder {
+	pub fn new(width: u16, height: u16) -> Self {
+		Self {
+			left_offset: 0,
+			top_offset: 0,
+			width,
+			height,
+			color_table: None,
+			indicies: vec![]
+		}
+	}
+
+	pub fn offsets(mut self, left_offset: u16, top_offset: u16) -> Self {
+		self.left_offset = left_offset;
+		self.top_offset = top_offset;
+		self
+	}
+
+	pub fn left_offset(mut self, offset: u16) -> Self {
+		self.left_offset = offset;
+		self
+	}
+
+	pub fn top_offset(mut self, offset: u16) -> Self {
+		self.top_offset = offset;
+		self
+	}
+
+	pub fn color_table(mut self, vec: Vec<Color>) -> Self {
+		if vec.len() == 0 || vec.len() > 256 {
+			//TODO: Throw error instead of panic
+			panic!("Color table has to be less than or 256 colors in size, and at least one");
+		}
+
+		self.color_table = Some(vec);
+
+		self
+	}
+
+	pub fn indicies(mut self, vec: Vec<u8>) -> Self {
+		self.indicies = vec;
+		self
+	}
+
+	//TODO: Make lzw_minimum_code_size optional. ONly needed with global color tables
+	pub fn write_to_vec(&self, lzw_minimum_code_size: u8) -> Vec<u8> {
+		let mut out = OutVec::new();
+
+		self.write_image_descriptor(&mut out)
+			.write_color_table(&mut out)
+			.write_image_data(&mut out, lzw_minimum_code_size);
+
+		out.vec()
+	}
+
+	fn write_image_descriptor(&self, out: &mut OutVec) -> &Self {
+		// Image seperator. At the start of every image descriptor
+		out.push_u8(0x2C)
+		.push_u16(self.left_offset)
+		.push_u16(self.top_offset)
+		.push_u16(self.width)
+		.push_u16(self.height);
+
+		// Taken from gifbuilder.rs
+		//TODO: deduplciate code
+		let mut packed: u8 = 0;
+		if let Some(ct) = &self.color_table {
+			packed |= 0b1000_0000; // Set the color table flag
+
+			let size = (ct.len() as f32).log2().ceil() - 1f32;
+			
+			packed |= size as u8;
+		}
+		//TODO: Interlace and Sort flags in packed
+		out.push_u8(packed);
+
+		self
+	}
+
+	fn write_color_table(&self, out: &mut OutVec) -> &Self {
+		if let Some(ct) = &self.color_table {
+			out.push_colors(&ct);
+		}
+
+		self
+	}
+
+	fn write_image_data(&self, out: &mut OutVec, minimum_code_size: u8) -> &Self {
+		let mut mcs = minimum_code_size;
+
+		//TODO: Deduplicate color table size code
+		if let Some(ct) = &self.color_table {
+			mcs = ((ct.len() as f32).log2().ceil() - 1f32) as u8;
+		}
+
+		if mcs < 2 {
+			// Must always be true: 2 <= mcs <= 8
+			mcs = 2;
+		}
+
+		// First write out the MCS
+		out.push_u8(mcs);
+
+		let compressed = LZW::encode(mcs, &self.indicies);
+		
+		for chunk in compressed.chunks(255) {
+			out.push_u8(chunk.len() as u8);
+			out.push_slice(chunk);
+		}
+		// Data block length 0 to indicate an end
+		out.push_u8(0x00);
+
+		self
+	}
+}
+
+#[cfg(test)]
+mod imagebuilder_test {
+	use super::*;
+
+	#[test]
+	fn write_to_vec() {
+		let colortable = vec![
+			Color::new(0, 0, 0),
+			Color::new(128, 0, 255)
+		];
+		let indicies = vec![0, 0, 0, 0, 0, 1, 1, 0, 0, 1, 1, 0, 0, 0, 0, 0];
+
+		let expected_out = vec![
+			0x2C, 0x00, 0x00, 0x00, 0x00, 0x04, 0x00, 0x04, 0x00, 0b1000_0000, // Image Descriptor
+			0, 0, 0, 128, 0, 255, // Color Table
+			0x02, 0x05, 0x84, 0x1D, 0x81, 0x7A, 0x50, 0x00 // Image Data
+		];
+		let actual_out = ImageBuilder::new(4, 4)
+			.color_table(colortable)
+			.indicies(indicies)
+			.write_to_vec(0);
+
+		assert_eq!(actual_out, expected_out);
+	}
+
+	#[test]
+	fn write_image_descriptor() {
+		let mut out = OutVec::new();
+		ImageBuilder::new(16, 16).offsets(1, 6).write_image_descriptor(&mut out);
+
+		assert_eq!(out.vec(), vec![0x2C, 0x01, 0x00, 0x06, 0x00, 0x10, 0x00, 0x10, 0x00, 0x00]);
+
+		let mut out = OutVec::new();
+		ImageBuilder::new(16, 16)
+			.offsets(1, 6)
+			.color_table(vec![Color::new(0, 0, 0)])
+			.write_image_descriptor(&mut out);
+
+		assert_eq!(out.vec(), vec![0x2C, 0x01, 0x00, 0x06, 0x00, 0x10, 0x00, 0x10, 0x00, 0b1000_0000]);
+	}
+
+	#[test]
+	fn write_color_table() {
+		let mut out = OutVec::new();
+		ImageBuilder::new(16, 16)
+			.color_table(vec![Color::new(1, 2, 3), Color::new(253, 254, 255)])
+			.write_color_table(&mut out);
+
+		assert_eq!(out.vec(), vec![0x01, 0x02, 0x03, 0xFD, 0xFE, 0xFF]);
+	}
+
+	#[test]
+	fn write_image_data() {
+		#[test]
+		fn encode() {
+			let indicies = vec![0, 0, 0, 0, 0, 1, 1, 0, 0, 1, 1, 0, 0, 0, 0, 0];
+			let output = vec![0x02, 0x05, 0x84, 0x1D, 0x81, 0x7A, 0x50, 0x00];
+
+			let mut out = OutVec::new();
+			ImageBuilder::new(16, 16)
+				.indicies(indicies)
+				.write_image_data(&mut out, 2);
+	
+			assert_eq!(out.vec(), output);
+		}
+	}
+}
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