🎉 Implement inner shadows (wasm) (#5767)

* 🎉 Implement inner shadows (wasm)

* 🐛 Fix reset canvas problem

---------

Co-authored-by: alonso.torres <alonso.torres@kaleidos.net>

render-wasm/src/shapes/shadows.rs

@@ -1,4 +1,4 @@
-use skia_safe::{self as skia, image_filters};
+use skia_safe::{self as skia, image_filters, ImageFilter};
 
 use super::Color;
 
@@ -26,10 +26,10 @@ impl Default for ShadowStyle {
 
 #[derive(Debug, Clone, Copy, PartialEq)]
 pub struct Shadow {
-    color: Color,
-    blur: f32,
-    spread: f32,
-    offset: (f32, f32),
+    pub color: Color,
+    pub blur: f32,
+    pub spread: f32,
+    pub offset: (f32, f32),
     style: ShadowStyle,
     hidden: bool,
 }
@@ -62,8 +62,21 @@ impl Shadow {
         self.hidden
     }
 
-    pub fn to_paint(&self, dilate: bool, scale: f32) -> skia::Paint {
+    pub fn to_paint(&self, scale: f32) -> skia::Paint {
         let mut paint = skia::Paint::default();
+
+        let image_filter = match self.style {
+            ShadowStyle::Drop => self.drop_shadow_filters(scale),
+            ShadowStyle::Inner => self.inner_shadow_filters(scale),
+        };
+
+        paint.set_image_filter(image_filter);
+        paint.set_anti_alias(true);
+
+        paint
+    }
+
+    fn drop_shadow_filters(&self, scale: f32) -> Option<ImageFilter> {
         let mut filter = image_filters::drop_shadow_only(
             (self.offset.0 * scale, self.offset.1 * scale),
             (self.blur * scale, self.blur * scale),
@@ -73,14 +86,41 @@ impl Shadow {
             None,
         );
 
-        if dilate {
+        if self.spread > 0. {
             filter =
                 image_filters::dilate((self.spread * scale, self.spread * scale), filter, None);
         }
 
-        paint.set_image_filter(filter);
-        paint.set_anti_alias(true);
+        filter
+    }
 
-        paint
+    fn inner_shadow_filters(&self, scale: f32) -> Option<ImageFilter> {
+        let sigma = self.blur * 0.5;
+        let mut filter = skia::image_filters::drop_shadow_only(
+            (self.offset.0 * scale, self.offset.1 * scale), // DPR?
+            (sigma * scale, sigma * scale),
+            skia::Color::BLACK,
+            None,
+            None,
+            None,
+        );
+
+        filter = skia::image_filters::color_filter(
+            skia::color_filters::blend(self.color, skia::BlendMode::SrcOut).unwrap(),
+            filter,
+            None,
+        );
+
+        if self.spread > 0. {
+            filter = skia::image_filters::dilate(
+                (self.spread * scale, self.spread * scale),
+                filter,
+                None,
+            );
+        }
+
+        filter = skia::image_filters::blend(skia::BlendMode::SrcIn, None, filter, None);
+
+        filter
     }
 }