Desktop: Render overlays with vello (#2965)

* Render overlays with vello

* Fix nix flake comments

* Rendering refactor with better names and code location

* Remove unnecessary overlay renders

* Post rebase fix

desktop/src/render/frame_buffer_ref.rs

@@ -0,0 +1,53 @@
+use thiserror::Error;
+
+pub(crate) struct FrameBufferRef<'a> {
+	buffer: &'a [u8],
+	width: usize,
+	height: usize,
+}
+impl<'a> FrameBufferRef<'a> {
+	pub(crate) fn new(buffer: &'a [u8], width: usize, height: usize) -> Result<Self, FrameBufferError> {
+		let fb = Self { buffer, width, height };
+		fb.validate_size()?;
+		Ok(fb)
+	}
+	pub(crate) fn buffer(&self) -> &[u8] {
+		self.buffer
+	}
+
+	pub(crate) fn width(&self) -> usize {
+		self.width
+	}
+
+	pub(crate) fn height(&self) -> usize {
+		self.height
+	}
+
+	fn validate_size(&self) -> Result<(), FrameBufferError> {
+		if self.buffer.len() != self.width * self.height * 4 {
+			Err(FrameBufferError::InvalidSize {
+				buffer_size: self.buffer.len(),
+				expected_size: self.width * self.height * 4,
+				width: self.width,
+				height: self.height,
+			})
+		} else {
+			Ok(())
+		}
+	}
+}
+impl<'a> std::fmt::Debug for FrameBufferRef<'a> {
+	fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+		f.debug_struct("FrameBuffer")
+			.field("width", &self.width)
+			.field("height", &self.height)
+			.field("len", &self.buffer.len())
+			.finish()
+	}
+}
+
+#[derive(Error, Debug)]
+pub(crate) enum FrameBufferError {
+	#[error("Invalid buffer size {buffer_size}, expected {expected_size} for width {width} multiplied with height {height} multiplied by 4 channels")]
+	InvalidSize { buffer_size: usize, expected_size: usize, width: usize, height: usize },
+}