correctly write palette padding

2 files changed, 18 insertions, 1 deletions

diff --git a/gifed/src/block/palette.rs b/gifed/src/block/palette.rs
index f2f4de3..d5cc696 100644
--- a/gifed/src/block/palette.rs
+++ b/gifed/src/block/palette.rs
@@ -15,6 +15,7 @@ impl Palette {
 		Self { table: vec![] }
 	}
 
+	//FIXME: gen- Second paragraph is incorrect
 	/// 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.
@@ -29,11 +30,17 @@ impl Palette {
 		self.packed_len() + 1
 	}
 
-	/// Returns the number of items in the table
+	/// Returns the number of colours in the pallette
 	pub fn len(&self) -> usize {
 		self.table.len()
 	}
 
+	/// Returns the number of items that the decoder *thinks* is in the palette.
+	/// This is 2^(n + 1) where n = [Palette::packed_len]
+	pub fn computed_len(&self) -> usize {
+		2usize.pow(self.packed_len() as u32 + 1)
+	}
+
 	/// Pushes a color on to the end of the table
 	pub fn push(&mut self, color: Color) {
 		self.table.push(color);
@@ -52,6 +59,14 @@ impl Palette {
 		None
 	}
 
+	/// How many padding bytes we need to write.
+	/// We need to pad the colour table because the size must be a power of two.
+	//TODO: gen- better docs
+	pub fn padding(&self) -> usize {
+		let comp = self.computed_len();
+		(comp as usize - self.len()) * 3
+	}
+
 	pub fn as_bytes(&self) -> Vec<u8> {
 		let mut bytes = Vec::with_capacity(self.table.len() * 3);
 		for color in &self.table {
diff --git a/gifed/src/writer/mod.rs b/gifed/src/writer/mod.rs
index 394d85f..493514b 100644
--- a/gifed/src/writer/mod.rs
+++ b/gifed/src/writer/mod.rs
@@ -47,7 +47,9 @@ impl<W: Write> Writer<W> {
 		this.write_all(&screen_descriptor.as_bytes())?;
 
 		if let Some(palette) = this.global_palette.as_ref() {
+			let padding: Vec<u8> = std::iter::repeat(0u8).take(palette.padding()).collect();
 			this.write_all(&palette.as_bytes())?;
+			this.write_all(&padding)?;
 		}
 
 		Ok(this)