feat: FeDropShadow (#2514)

# Summary

Continuation of #2362 introducing highly requested ✨ `FeDropShadow` ✨
filter. This addition is straightforward since it's essentially a
shorthand (as specified in the spec) for filters that are already
implemented: https://www.w3.org/TR/filter-effects-1/#feDropShadowElement

<img width="532" alt="image"
src="https://github.com/user-attachments/assets/b221ee4c-d8b0-469b-acb0-71224fb2b1e0">

## Test Plan

Example app -> Filters -> FeDropShadow

## Compatibility

| OS      | Implemented |
| ------- | :---------: |
| iOS     |    ✅      |
| macOS   |    ✅      |
| Android |    ✅      |
| Web     |    ✅      |

USAGE.md

@@ -1301,7 +1301,9 @@ Filter effects are a way of processing an element’s rendering before it is dis
 The following filters have been implemented:
 
 - FeBlend
+- FeComposite
 - FeColorMatrix
+- FeDropShadow
 - FeFlood
 - FeGaussianBlur
 - FeMerge
@@ -1310,11 +1312,9 @@ The following filters have been implemented:
 Not supported yet:
 
 - FeComponentTransfer
-- FeComposite
 - FeConvolveMatrix
 - FeDiffuseLighting
 - FeDisplacementMap
-- FeDropShadow
 - FeFuncA
 - FeFuncB
 - FeFuncG

apps/common/example/examples/Filters/FeDropShadow.tsx

@@ -0,0 +1,59 @@
+import React from 'react';
+import {
+  Circle,
+  FeDropShadow,
+  FeFlood,
+  Filter,
+  Rect,
+  Svg,
+} from 'react-native-svg';
+
+BasicMDN.title = 'Basic MDN example';
+function BasicMDN() {
+  return (
+    <Svg viewBox="0 0 30 10" width="300" height="100">
+      <Filter id="shadow">
+        <FeDropShadow dx="0.2" dy="0.4" stdDeviation="0.2" />
+      </Filter>
+      <Filter id="shadow2">
+        <FeDropShadow dx="0" dy="0" stdDeviation="5" floodColor="cyan" />
+      </Filter>
+      <Filter id="shadow3">
+        <FeDropShadow
+          dx="-0.8"
+          dy="-0.8"
+          stdDeviation="0"
+          floodColor="pink"
+          floodOpacity="0.5"
+        />
+      </Filter>
+      <Circle cx="5" cy="50%" r="4" fill="pink" filter="url(#shadow)" />
+      <Circle cx="15" cy="50%" r="4" fill="pink" filter="url(#shadow2)" />
+      <Circle cx="25" cy="50%" r="4" fill="pink" filter="url(#shadow3)" />
+    </Svg>
+  );
+}
+
+const icon = (
+  <Svg height="30" width="30" viewBox="0 0 140 140">
+    <Filter
+      id="floodFilterIcon"
+      x="50%"
+      filterUnits="userSpaceOnUse"
+      primitiveUnits="userSpaceOnUse">
+      <FeFlood
+        y="-10%"
+        x="10%"
+        width="50%"
+        height="50%"
+        floodColor="yellow"
+        floodOpacity="0.5"
+      />
+    </Filter>
+    <Rect x="0" y="0" width="100" height="100" fill="blue" />
+    <Circle cx="50" cy="50" r="40" filter="url(#floodFilterIcon)" />
+  </Svg>
+);
+const samples = [BasicMDN];
+
+export {icon, samples};

apps/common/example/examples/Filters/index.tsx

@@ -3,6 +3,7 @@ import Svg, {Circle} from 'react-native-svg';
 import * as FeBlend from './FeBlend';
 import * as FeColorMatrix from './FeColorMatrix';
 import * as FeComposite from './FeComposite';
+import * as FeDropShadow from './FeDropShadow';
 import * as FeFlood from './FeFlood';
 import * as FeGaussianBlur from './FeGaussianBlur';
 import * as FeMerge from './FeMerge';
@@ -13,6 +14,7 @@ const samples = {
   FeBlend,
   FeColorMatrix,
   FeComposite,
+  FeDropShadow,
   FeFlood,
   FeGaussianBlur,
   FeMerge,

src/elements/filters/FeDropShadow.tsx

@@ -1,12 +1,20 @@
+import { ColorValue } from 'react-native';
 import { NumberArray, NumberProp } from '../../lib/extract/types';
-import { warnUnimplementedFilter } from '../../lib/util';
+import FeFlood from './FeFlood';
+import FeGaussianBlur from './FeGaussianBlur';
+import FeMerge from './FeMerge';
+import FeMergeNode from './FeMergeNode';
+import FeOffset from './FeOffset';
 import FilterPrimitive from './FilterPrimitive';
+import FeComposite from './FeComposite';
 
 export interface FeDropShadowProps {
   in?: string;
   stdDeviation?: NumberArray;
   dx?: NumberProp;
   dy?: NumberProp;
+  floodColor?: ColorValue;
+  floodOpacity?: NumberProp;
 }
 
 export default class FeDropShadow extends FilterPrimitive<FeDropShadowProps> {
@@ -17,7 +25,21 @@ export default class FeDropShadow extends FilterPrimitive<FeDropShadowProps> {
   };
 
   render() {
-    warnUnimplementedFilter();
-    return null;
+    const { stdDeviation, in: in1 = 'SourceGraphic', dx, dy } = this.props;
+    return (
+      <>
+        <FeGaussianBlur in={in1} stdDeviation={stdDeviation} />
+        <FeOffset dx={dx} dy={dy} result="offsetblur" />
+        <FeFlood
+          floodColor={this.props.floodColor}
+          floodOpacity={this.props.floodOpacity}
+        />
+        <FeComposite in2="offsetblur" operator="in" />
+        <FeMerge>
+          <FeMergeNode />
+          <FeMergeNode in={in1} />
+        </FeMerge>
+      </>
+    );
   }
 }