🎉 Implement drawing with blend mode (single fill)

common/src/app/common/types/shape/impl.cljc

@@ -20,6 +20,7 @@
 (defonce wasm-set-shape-transform (constantly nil))
 (defonce wasm-set-shape-rotation (constantly nil))
 (defonce wasm-set-shape-fills (constantly nil))
+(defonce wasm-set-shape-blend-mode (constantly nil))
 (defonce wasm-set-shape-children (constantly nil))
 
 (cr/defrecord Shape [id name type x y width height rotation selrect points
@@ -119,6 +120,7 @@
          :rotation   (wasm-set-shape-rotation v)
          :transform  (wasm-set-shape-transform v)
          :fills      (wasm-set-shape-fills v)
+         :blend-mode (wasm-set-shape-blend-mode v)
          :shapes     (wasm-set-shape-children v)
          nil))
      (let [delegate  (.-delegate ^ShapeProxy coll)

frontend/src/app/render_wasm.cljs

@@ -74,6 +74,30 @@
           [r g b] (cc/hex->rgb (:fill-color fill))]
       (._add_shape_solid_fill ^js internal-module r g b a))))
 
+(defn set-shape-blend-mode
+  [blend-mode]
+  ;; These values correspond to skia::BlendMode representation
+  ;; https://rust-skia.github.io/doc/skia_safe/enum.BlendMode.html
+  (let [encoded-blend (case blend-mode
+    :normal 3
+    :darken 16
+    :multiply 24
+    :color-burn 19
+    :lighten 17
+    :screen 14
+    :color-dodge 18
+    :overlay 15
+    :soft-light 21
+    :hard-light 20
+    :difference 22
+    :exclusion 23
+    :hue 25
+    :saturation 26
+    :color 27
+    :luminosity 28
+    3)]
+    (._set_shape_blend_mode ^js internal-module encoded-blend)))
+
 (defn set-objects
   [objects]
   (let [shapes        (into [] xform (vals objects))
@@ -86,12 +110,14 @@
               rotation   (dm/get-prop shape :rotation)
               transform  (dm/get-prop shape :transform)
               fills      (dm/get-prop shape :fills)
-              children  (dm/get-prop shape :shapes)]
+              children   (dm/get-prop shape :shapes)
+              blend-mode (dm/get-prop shape :blend-mode)]
           (use-shape id)
           (set-shape-selrect selrect)
           (set-shape-rotation rotation)
           (set-shape-transform transform)
           (set-shape-fills fills)
+          (set-shape-blend-mode blend-mode)
           (set-shape-children children)
           (recur (inc index)))))))
 
@@ -155,4 +181,5 @@
 (set! app.common.types.shape.impl/wasm-set-shape-transform set-shape-transform)
 (set! app.common.types.shape.impl/wasm-set-shape-rotation set-shape-rotation)
 (set! app.common.types.shape.impl/wasm-set-shape-fills set-shape-fills)
+(set! app.common.types.shape.impl/wasm-set-shape-blend-mode set-shape-blend-mode)
 (set! app.common.types.shape.impl/wasm-set-shape-children set-shape-children)

render-wasm/src/main.rs

@@ -128,6 +128,14 @@ pub extern "C" fn clear_shape_fills() {
     }
 }
 
+#[no_mangle]
+pub extern "C" fn set_shape_blend_mode(mode: i32) {
+    let state = unsafe { STATE.as_mut() }.expect("got an invalid state pointer");
+    if let Some(shape) = state.current_shape() {
+        shape.set_blend_mode(shapes::BlendMode::from(mode));
+    }
+}
+
 fn main() {
     render::init_gl();
 }

render-wasm/src/render.rs

@@ -141,7 +141,10 @@ fn render_single_shape(surface: &mut skia::Surface, shape: &Shape) {
 
     surface.canvas().concat(&matrix);
 
+    // TODO: use blend mode for the shape as a whole, not in each fill
     for fill in shape.fills().rev() {
-        surface.canvas().draw_rect(r, &fill.to_paint());
+        let mut p = fill.to_paint();
+        p.set_blend_mode(shape.blend_mode.into());
+        surface.canvas().draw_rect(r, &p);
     }
 }

render-wasm/src/shapes.rs

@@ -72,7 +72,6 @@ impl Fill {
                 p.set_color(*color);
                 p.set_style(skia::PaintStyle::Fill);
                 p.set_anti_alias(true);
-                // TODO: get proper blend mode. See https://tree.taiga.io/project/penpot/task/9275
                 p.set_blend_mode(skia::BlendMode::SrcOver);
                 p
             }
@@ -80,15 +79,43 @@ impl Fill {
     }
 }
 
+#[derive(Debug, PartialEq, Clone, Copy)]
+pub struct BlendMode(skia::BlendMode);
+
+impl Default for BlendMode {
+    fn default() -> Self {
+        BlendMode(skia::BlendMode::SrcOver)
+    }
+}
+
+impl From<i32> for BlendMode {
+    fn from(value: i32) -> Self {
+        if value <= skia::BlendMode::Luminosity as i32 {
+            unsafe { Self(std::mem::transmute(value)) }
+        } else {
+            Self::default()
+        }
+    }
+}
+
+impl Into<skia::BlendMode> for BlendMode {
+    fn into(self) -> skia::BlendMode {
+        match self {
+            Self(skia_blend) => skia_blend,
+        }
+    }
+}
+
 #[derive(Debug, Clone)]
 pub struct Shape {
     pub id: Uuid,
-    pub children: Vec::<Uuid>,
+    pub children: Vec<Uuid>,
     pub kind: Kind,
     pub selrect: Rect,
     pub transform: Matrix,
     pub rotation: f32,
     fills: Vec<Fill>,
+    pub blend_mode: BlendMode,
 }
 
 impl Shape {
@@ -101,6 +128,7 @@ impl Shape {
             transform: Matrix::identity(),
             rotation: 0.,
             fills: vec![],
+            blend_mode: BlendMode::default(),
         }
     }
 
@@ -127,4 +155,8 @@ impl Shape {
     pub fn clear_fills(&mut self) {
         self.fills.clear();
     }
+
+    pub fn set_blend_mode(&mut self, mode: BlendMode) {
+        self.blend_mode = mode;
+    }
 }