Layer opacity (#312)

Closes #187

* Add layer opacity input

* Improve Rust code cleanliness

core/document/src/document.rs

@@ -412,15 +412,22 @@ impl Document {
 			}
 			Operation::SetLayerBlendMode { path, blend_mode } => {
 				self.mark_as_dirty(path)?;
-				self.layer_mut(&path).unwrap().blend_mode = *blend_mode;
+				self.layer_mut(path)?.blend_mode = *blend_mode;
+
+				let path = path.as_slice()[..path.len() - 1].to_vec();
+
+				Some(vec![DocumentResponse::DocumentChanged, DocumentResponse::FolderChanged { path }])
+			}
+			Operation::SetLayerOpacity { path, opacity } => {
+				self.mark_as_dirty(path)?;
+				self.layer_mut(path)?.opacity = *opacity;
 
 				let path = path.as_slice()[..path.len() - 1].to_vec();
 
 				Some(vec![DocumentResponse::DocumentChanged, DocumentResponse::FolderChanged { path }])
 			}
 			Operation::FillLayer { path, color } => {
-				let layer = self.layer_mut(path).unwrap();
-				layer.style.set_fill(layers::style::Fill::new(*color));
+				self.layer_mut(path)?.style.set_fill(layers::style::Fill::new(*color));
 				self.mark_as_dirty(path)?;
 				Some(vec![DocumentResponse::DocumentChanged])
 			}

core/document/src/layers/mod.rs

@@ -175,6 +175,7 @@ pub struct Layer {
 	pub thumbnail_cache: String,
 	pub cache_dirty: bool,
 	pub blend_mode: BlendMode,
+	pub opacity: f64,
 }
 
 impl Layer {
@@ -189,6 +190,7 @@ impl Layer {
 			thumbnail_cache: String::new(),
 			cache_dirty: true,
 			blend_mode: BlendMode::Normal,
+			opacity: 1.,
 		}
 	}
 
@@ -203,8 +205,9 @@ impl Layer {
 			self.cache.clear();
 			let _ = write!(
 				self.cache,
-				r#"<g style="mix-blend-mode: {}">{}</g>"#,
+				r#"<g style="mix-blend-mode: {}; opacity: {}">{}</g>"#,
 				self.blend_mode.to_svg_style_name(),
+				self.opacity,
 				self.thumbnail_cache.as_str()
 			);
 

core/document/src/operation.rs

@@ -77,6 +77,10 @@ pub enum Operation {
 		path: Vec<LayerId>,
 		blend_mode: BlendMode,
 	},
+	SetLayerOpacity {
+		path: Vec<LayerId>,
+		opacity: f64,
+	},
 	FillLayer {
 		path: Vec<LayerId>,
 		color: Color,