feat: Add baseColor to Shadow3DDecorator (#3375)

The Shadow3DDecorator is very useful, but the shadow defaults to being
pure black. While this is fine in most cases, sometimes a designer might
request something a little bit different, so this change to allow the
base color of the shadow to be changed if so desired.

packages/flame/lib/src/rendering/shadow3d_decorator.dart

@@ -1,7 +1,8 @@
 import 'dart:ui';
 
+import 'package:flame/src/palette.dart';
 import 'package:flame/src/rendering/decorator.dart';
-import 'package:vector_math/vector_math_64.dart';
+import 'package:vector_math/vector_math_64.dart' show Matrix4, Vector2;
 
 /// [Shadow3DDecorator] casts a realistic-looking shadow from the component
 /// onto the ground.
@@ -24,13 +25,15 @@ class Shadow3DDecorator extends Decorator {
     double? yScale,
     double? blur,
     double? opacity,
+    Color? baseColor,
   })  : _base = base?.clone() ?? Vector2.zero(),
         _ascent = ascent ?? 0,
         _angle = angle ?? -1.4,
         _shift = xShift ?? 100.0,
         _scale = yScale ?? 1.0,
         _blur = blur ?? 0,
-        _opacity = opacity ?? 0.6;
+        _opacity = opacity ?? 0.6,
+        _baseColor = baseColor ?? BasicPalette.black.color;
 
   /// Coordinates of the point where the component "touches the ground". If the
   /// component is airborne (i.e. [ascent] is non-zero), then this should be the
@@ -117,10 +120,18 @@ class Shadow3DDecorator extends Decorator {
     _paint = null;
   }
 
+  /// Shadow's base color before opacity. This defaults to pitch-black.
+  Color get baseColor => _baseColor;
+  Color _baseColor;
+  set baseColor(Color value) {
+    _baseColor = value;
+    _paint = null;
+  }
+
   Paint? _paint;
   Paint _makePaint() {
     final paint = Paint();
-    final color = Color.fromRGBO(0, 0, 0, opacity);
+    final color = baseColor.withOpacity(opacity);
     paint.colorFilter = ColorFilter.mode(color, BlendMode.srcIn);
     if (_blur > 0) {
       paint.imageFilter = ImageFilter.blur(sigmaX: blur, sigmaY: blur / _scale);

packages/flame/test/rendering/shadow3d_decorator_test.dart

@@ -1,6 +1,7 @@
 import 'dart:ui';
 
 import 'package:flame/components.dart';
+import 'package:flame/palette.dart';
 import 'package:flame/rendering.dart';
 import 'package:flame_test/flame_test.dart';
 import 'package:flutter_test/flutter_test.dart';
@@ -16,6 +17,7 @@ void main() {
       expect(decorator.yScale, 1.0);
       expect(decorator.blur, 0.0);
       expect(decorator.opacity, 0.6);
+      expect(decorator.baseColor, BasicPalette.black.color);
     });
 
     testGolden(
@@ -79,7 +81,8 @@ void main() {
               ..xShift = 250.0
               ..yScale = 1.5
               ..opacity = 0.4
-              ..blur = 1.0,
+              ..blur = 1.0
+              ..baseColor = BasicPalette.red.color,
           ),
         ]);
       },