premultiplied alpha in draw functions

src/color.rs

@@ -102,6 +102,12 @@ impl Color {
         self.a = self.r.clamp(0., 1.);
         self
     }
+
+    pub fn premultiply_alpha(&mut self) {
+        self.r *= self.a;
+        self.g *= self.a;
+        self.b *= self.a;
+    }
 }
 
 impl Mul<Color> for Color {

src/draw/combined.rs

@@ -16,6 +16,7 @@ pub struct CombinedRenderable {
 
 pub struct CombinedDrawer {
     pub cull_direction: CullDirection,
+    pub premultiplied_alpha: bool,
 }
 
 /// A combined drawer with a mesh combining optimization.
@@ -128,8 +129,13 @@ impl CombinedDrawer {
             let (color, dark_color) = if let Some(mesh_attachment) =
                 slot.attachment().and_then(|a| a.as_mesh())
             {
-                let color = mesh_attachment.color() * slot.color() * skeleton.color();
-                let dark_color = Color::new_rgba(0., 0., 0., 1.);
+                let mut color = mesh_attachment.color() * slot.color() * skeleton.color();
+                let mut dark_color = Color::new_rgba(0., 0., 0., 0.);
+                if self.premultiplied_alpha {
+                    color.premultiply_alpha();
+                    dark_color.premultiply_alpha();
+                    dark_color.a = 1.;
+                }
 
                 uvs.resize(
                     vertex_base as usize + mesh_attachment.world_vertices_length() as usize,
@@ -197,8 +203,13 @@ impl CombinedDrawer {
 
                 (color, dark_color)
             } else if let Some(region_attachment) = slot.attachment().and_then(|a| a.as_region()) {
-                let color = region_attachment.color() * slot.color() * skeleton.color();
-                let dark_color = Color::new_rgba(0., 0., 0., 1.);
+                let mut color = region_attachment.color() * slot.color() * skeleton.color();
+                let mut dark_color = Color::new_rgba(0., 0., 0., 0.);
+                if self.premultiplied_alpha {
+                    color.premultiply_alpha();
+                    dark_color.premultiply_alpha();
+                    dark_color.a = 1.;
+                }
 
                 for i in 0..4 {
                     vertices.push([

src/draw/simple.rs

@@ -11,13 +11,14 @@ pub struct SimpleRenderable {
     pub uvs: Vec<[f32; 2]>,
     pub indices: Vec<u16>,
     pub color: Color,
-    pub dark_color: Option<Color>,
+    pub dark_color: Color,
     pub blend_mode: BlendMode,
     pub attachment_renderer_object: Option<*const c_void>,
 }
 
 pub struct SimpleDrawer {
     pub cull_direction: CullDirection,
+    pub premultiplied_alpha: bool,
 }
 
 /// A simple drawer with no optimizations.
@@ -246,14 +247,25 @@ impl SimpleDrawer {
             };
 
             color *= slot.color() * skeleton.color();
+            if self.premultiplied_alpha {
+                color.premultiply_alpha();
+            }
+
+            let mut dark_color = slot
+                .dark_color()
+                .unwrap_or(Color::new_rgba(0.0, 0.0, 0.0, 0.0));
+            if self.premultiplied_alpha {
+                dark_color.premultiply_alpha();
+                dark_color.a = 1.0;
+            }
 
             renderables.push(SimpleRenderable {
-                slot_index: slot_index,
+                slot_index,
                 vertices,
                 uvs,
                 indices,
                 color,
-                dark_color: slot.dark_color(),
+                dark_color,
                 blend_mode: slot.data().blend_mode(),
                 attachment_renderer_object,
             });

src/skeleton_controller.rs

@@ -86,6 +86,7 @@ impl SkeletonController {
     pub fn renderables(&mut self) -> Vec<SkeletonRenderable> {
         let renderables = SimpleDrawer {
             cull_direction: self.settings.cull_direction,
+            premultiplied_alpha: self.settings.premultiplied_alpha,
         }
         .draw(&mut self.skeleton, Some(&mut self.clipper));
         renderables
@@ -112,7 +113,7 @@ pub struct SkeletonRenderable {
     pub uvs: Vec<[f32; 2]>,
     pub indices: Vec<u16>,
     pub color: Color,
-    pub dark_color: Option<Color>,
+    pub dark_color: Color,
     pub blend_mode: BlendMode,
     pub premultiplied_alpha: bool,
     pub attachment_renderer_object: Option<*const c_void>,