fix longstanding annoying in SceneBuilder ctor

SceneBuilder::new() now takes &mut Scene or &mut SceneFragment

piet-scene/src/scene/builder.rs

@@ -30,18 +30,30 @@ pub struct SceneBuilder<'a> {
 impl<'a> SceneBuilder<'a> {
     /// Creates a new builder for filling a scene. Any current content in the scene
     /// will be cleared.
+    #[deprecated = "use SceneBuilder::new() instead"]
     pub fn for_scene(scene: &'a mut Scene) -> Self {
-        Self::new(&mut scene.data, false)
+        Self::new_inner(&mut scene.data, false)
     }
 
     /// Creates a new builder for filling a scene fragment. Any current content in
     /// the fragment will be cleared.    
+    #[deprecated = "use SceneBuilder::new() instead"]
     pub fn for_fragment(fragment: &'a mut SceneFragment) -> Self {
-        Self::new(&mut fragment.data, true)
+        Self::new_inner(&mut fragment.data, true)
+    }
+
+    /// Creates a new scene builder for a scene or scene fragment. Any content will be
+    /// cleared. The types accepted for the scene parameter are `&mut Scene` or
+    /// `&mut SceneFragment`.
+    pub fn new(scene: impl Into<AnyScene<'a>>) -> Self {
+        match scene.into() {
+            AnyScene::Scene(scene) => Self::new_inner(&mut scene.data, false),
+            AnyScene::Fragment(fragment) => Self::new_inner(&mut fragment.data, true),
+        }
     }
 
     /// Creates a new builder for constructing a scene.
-    fn new(scene: &'a mut SceneData, is_fragment: bool) -> Self {
+    fn new_inner(scene: &'a mut SceneData, is_fragment: bool) -> Self {
         scene.reset(is_fragment);
         Self {
             scene,
@@ -276,6 +288,26 @@ impl<'a> SceneBuilder<'a> {
     }
 }
 
+/// Helper for constructing a scene builder.
+#[doc(hidden)]
+pub enum AnyScene<'a> {
+    Scene(&'a mut Scene),
+    Fragment(&'a mut SceneFragment),
+}
+
+impl<'a> From<&'a mut Scene> for AnyScene<'a> {
+    fn from(scene: &'a mut Scene) -> Self {
+        Self::Scene(scene)
+    }
+}
+
+impl<'a> From<&'a mut SceneFragment> for AnyScene<'a> {
+    fn from(scene: &'a mut SceneFragment) -> Self {
+        Self::Fragment(scene)
+    }
+}
+
+
 fn encode_blend_mode(mode: BlendMode) -> u32 {
     (mode.mix as u32) << 8 | mode.compose as u32
 }

piet-wgsl/examples/winit/src/main.rs

@@ -70,7 +70,7 @@ async fn run() -> Result<()> {
             current_frame += 1;
             let width = surface.config.width;
             let height = surface.config.height;
-            let mut builder = SceneBuilder::for_scene(&mut scene);
+            let mut builder = SceneBuilder::new(&mut scene);
             const N_SCENES: usize = 6;
             match scene_ix % N_SCENES {
                 0 => test_scene::render_anim_frame(&mut builder, &mut simple_text, current_frame),

piet-wgsl/examples/winit/src/test_scene.rs

@@ -265,7 +265,7 @@ fn render_blend_square(sb: &mut SceneBuilder, blend: BlendMode, transform: Affin
 #[allow(unused)]
 fn blend_square(blend: BlendMode) -> SceneFragment {
     let mut fragment = SceneFragment::default();
-    let mut sb = SceneBuilder::for_fragment(&mut fragment);
+    let mut sb = SceneBuilder::new(&mut fragment);
     render_blend_square(&mut sb, blend, Affine::IDENTITY);
     sb.finish();
     fragment