Unify encoding of Scene/SceneFragment

In a move toward dropping the SceneFragment and SceneBuilder types, this unifies the underlying encoding of Scene and SceneFragment. Specifically, we no longer encode an initial transform and style for Scene.

This causes the transform and style indices in the path tag monoid to be off by one. I chose the simple approach of subtracting 1 from each in the combine_tag_monoid() functions in both GPU and CPU code to correct this.

crates/encoding/src/encoding.rs

diff --git a/crates/encoding/src/encoding.rs b/crates/encoding/src/encoding.rs
index a9eee83..40db12d 100644
--- a/crates/encoding/src/encoding.rs
+++ b/crates/encoding/src/encoding.rs
@@ -65,7 +65,7 @@
     }
 
     /// Clears the encoding.
-    pub fn reset(&mut self, is_fragment: bool) {
+    pub fn reset(&mut self) {
         self.transforms.clear();
         self.path_tags.clear();
         self.path_data.clear();
@@ -79,10 +79,6 @@
         self.flags = 0;
         #[cfg(feature = "full")]
         self.resources.reset();
-        if !is_fragment {
-            self.transforms.push(Transform::IDENTITY);
-            self.styles.push(Style::from_fill(Fill::NonZero));
-        }
     }
 
     /// Appends another encoding to this one with an optional transform.

crates/encoding/src/glyph_cache.rs

diff --git a/crates/encoding/src/glyph_cache.rs b/crates/encoding/src/glyph_cache.rs
index 330f6d7..925160e 100644
--- a/crates/encoding/src/glyph_cache.rs
+++ b/crates/encoding/src/glyph_cache.rs
@@ -28,7 +28,7 @@
 
 impl GlyphCache {
     pub fn clear(&mut self) {
-        self.encoding.reset(true);
+        self.encoding.reset();
         self.glyphs.clear();
     }
 

shader/flatten.wgsl

diff --git a/shader/flatten.wgsl b/shader/flatten.wgsl
index f90e265..79748de 100644
--- a/shader/flatten.wgsl
+++ b/shader/flatten.wgsl
@@ -476,6 +476,10 @@
     // TODO: this can be a read buf overflow. Conditionalize by tag byte?
     tm = combine_tag_monoid(tag_monoids[ix >> 2u], tm);
     var tag_byte = (tag_word >> shift) & 0xffu;
+    // We no longer encode an initial transform and style so these
+    // are off by one.
+    tm.trans_ix -= 1u;
+    tm.style_ix -= STYLE_SIZE_IN_WORDS;
     return PathTagData(tag_byte, tm);
 }
 

src/cpu_shader/flatten.rs

diff --git a/src/cpu_shader/flatten.rs b/src/cpu_shader/flatten.rs
index fba7173..7b31d74 100644
--- a/src/cpu_shader/flatten.rs
+++ b/src/cpu_shader/flatten.rs
@@ -524,6 +524,10 @@
     if tag_byte != 0 {
         tm = tag_monoids[ix >> 2].combine(&tm);
     }
+    // We no longer encode an initial transform and style so these
+    // are off by one.
+    tm.trans_ix -= 1;
+    tm.style_ix -= core::mem::size_of::<Style>() as u32 / 4;
     PathTagData {
         tag_byte,
         monoid: tm,

src/scene.rs

diff --git a/src/scene.rs b/src/scene.rs
index 86ebe97..9b968fa 100644
--- a/src/scene.rs
+++ b/src/scene.rs
@@ -73,18 +73,18 @@
     /// Creates a new builder for filling a scene. Any current content in the scene
     /// will be cleared.
     pub fn for_scene(scene: &'a mut Scene) -> Self {
-        Self::new(&mut scene.data, false)
+        Self::new(&mut scene.data)
     }
 
     /// Creates a new builder for filling a scene fragment. Any current content in
     /// the fragment will be cleared.    
     pub fn for_fragment(fragment: &'a mut SceneFragment) -> Self {
-        Self::new(&mut fragment.data, true)
+        Self::new(&mut fragment.data)
     }
 
     /// Creates a new builder for constructing a scene.
-    fn new(scene: &'a mut Encoding, is_fragment: bool) -> Self {
-        scene.reset(is_fragment);
+    fn new(scene: &'a mut Encoding) -> Self {
+        scene.reset();
         Self { scene }
     }