diff --git a/piet-gpu-derive/src/glsl.rs b/piet-gpu-derive/src/glsl.rs
index 96cb3c3..d9f08f3 100644
--- a/piet-gpu-derive/src/glsl.rs
+++ b/piet-gpu-derive/src/glsl.rs
@@ -29,6 +29,7 @@ pub fn gen_glsl(module: &LayoutModule) -> String {
             (size, LayoutTypeDef::Enum(en)) => {
                 gen_enum_def(&mut r, name, en);
                 gen_item_def(&mut r, name, size.size);
+                gen_tag_def(&mut r, name);
             }
         }
     }
@@ -92,6 +93,13 @@ fn gen_item_def(r: &mut String, name: &str, size: usize) {
     writeln!(r, "}}\n").unwrap();
 }
 
+fn gen_tag_def(r: &mut String, name: &str) {
+    writeln!(r, "struct {}Tag {{", name).unwrap();
+    writeln!(r, "   uint tag;").unwrap();
+    writeln!(r, "   uint flags;").unwrap();
+    writeln!(r, "}};\n").unwrap();
+}
+
 fn gen_struct_read(
     r: &mut String,
     bufname: &str,
@@ -143,12 +151,13 @@ fn gen_enum_read(
     variants: &[(String, Vec<(usize, LayoutType)>)],
 ) {
     if is_mem {
-        writeln!(r, "uint {}_tag(Alloc a, {}Ref ref) {{", name, name).unwrap();
-        writeln!(r, "    return read_mem(a, ref.offset >> 2);").unwrap();
+        writeln!(r, "{}Tag {}_tag(Alloc a, {}Ref ref) {{", name, name, name).unwrap();
+        writeln!(r, "    uint tag_and_flags = read_mem(a, ref.offset >> 2);").unwrap();
     } else {
-        writeln!(r, "uint {}_tag({}Ref ref) {{", name, name).unwrap();
-        writeln!(r, "    return {}[ref.offset >> 2];", bufname).unwrap();
+        writeln!(r, "{}Tag {}_tag({}Ref ref) {{", name, name, name).unwrap();
+        writeln!(r, "    uint tag_and_flags = {}[ref.offset >> 2];", bufname).unwrap();
     }
+    writeln!(r, "    return {}Tag(tag_and_flags & 0xffff, tag_and_flags >> 16);", name).unwrap();
     writeln!(r, "}}\n").unwrap();
     for (var_name, payload) in variants {
         let payload_ix = if payload.len() == 1 {
@@ -555,6 +564,49 @@ fn gen_enum_write(
                 }
                 writeln!(r, "}}\n").unwrap();
             }
+        } else if payload.len() == 2 && matches!(payload[0].1.ty, GpuType::Scalar(GpuScalar::TagFlags)) {
+            if let GpuType::InlineStruct(structname) = &payload[1].1.ty {
+                if is_mem {
+                    writeln!(
+                        r,
+                        "void {}_{}_write(Alloc a, {}Ref ref, uint flags, {} s) {{",
+                        name, var_name, name, structname
+                    )
+                    .unwrap();
+                    writeln!(
+                        r,
+                        "    write_mem(a, ref.offset >> 2, (flags << 16) | {}_{});",
+                        name, var_name
+                    )
+                    .unwrap();
+                    writeln!(
+                        r,
+                        "    {}_write(a, {}Ref(ref.offset + {}), s);",
+                        structname, structname, payload[0].0
+                    )
+                    .unwrap();
+                } else {
+                    writeln!(
+                        r,
+                        "void {}_{}_write({}Ref ref, uint flags, {} s) {{",
+                        name, var_name, name, structname
+                    )
+                    .unwrap();
+                    writeln!(
+                        r,
+                        "    {}[ref.offset >> 2] = (flags << 16) | {}_{};",
+                        bufname, name, var_name
+                    )
+                    .unwrap();
+                    writeln!(
+                        r,
+                        "    {}_write({}Ref(ref.offset + {}), s);",
+                        structname, structname, payload[0].0
+                    )
+                    .unwrap();
+                }
+                writeln!(r, "}}\n").unwrap();
+            }
         }
         // TODO: support for variants that aren't one struct.
     }
diff --git a/piet-gpu/shader/annotated.h b/piet-gpu/shader/annotated.h
index 40ded79..63d4bdb 100644
--- a/piet-gpu/shader/annotated.h
+++ b/piet-gpu/shader/annotated.h
@@ -79,6 +79,11 @@ AnnotatedRef Annotated_index(AnnotatedRef ref, uint index) {
     return AnnotatedRef(ref.offset + index * Annotated_size);
 }
 
+struct AnnotatedTag {
+   uint tag;
+   uint flags;
+};
+
 AnnoFill AnnoFill_read(Alloc a, AnnoFillRef ref) {
     uint ix = ref.offset >> 2;
     uint raw0 = read_mem(a, ix + 0);
@@ -170,8 +175,9 @@ void AnnoClip_write(Alloc a, AnnoClipRef ref, AnnoClip s) {
     write_mem(a, ix + 3, floatBitsToUint(s.bbox.w));
 }
 
-uint Annotated_tag(Alloc a, AnnotatedRef ref) {
-    return read_mem(a, ref.offset >> 2);
+AnnotatedTag Annotated_tag(Alloc a, AnnotatedRef ref) {
+    uint tag_and_flags = read_mem(a, ref.offset >> 2);
+    return AnnotatedTag(tag_and_flags & 0xffff, tag_and_flags >> 16);
 }
 
 AnnoStroke Annotated_Stroke_read(Alloc a, AnnotatedRef ref) {
diff --git a/piet-gpu/shader/backdrop.comp b/piet-gpu/shader/backdrop.comp
index 49de925..03212c9 100644
--- a/piet-gpu/shader/backdrop.comp
+++ b/piet-gpu/shader/backdrop.comp
@@ -46,7 +46,7 @@ void main() {
     // Work assignment: 1 thread : 1 path element
     uint row_count = 0;
     if (element_ix < conf.n_elements) {
-        uint tag = Annotated_tag(conf.anno_alloc, ref);
+        uint tag = Annotated_tag(conf.anno_alloc, ref).tag;
         switch (tag) {
         case Annotated_Fill:
         case Annotated_FillImage:
diff --git a/piet-gpu/shader/backdrop.spv b/piet-gpu/shader/backdrop.spv
index f33a50b..932192a 100644
Binary files a/piet-gpu/shader/backdrop.spv and b/piet-gpu/shader/backdrop.spv differ
diff --git a/piet-gpu/shader/binning.comp b/piet-gpu/shader/binning.comp
index 3a63ac2..c5cc806 100644
--- a/piet-gpu/shader/binning.comp
+++ b/piet-gpu/shader/binning.comp
@@ -56,7 +56,7 @@ void main() {
     AnnotatedRef ref = AnnotatedRef(conf.anno_alloc.offset + element_ix * Annotated_size);
     uint tag = Annotated_Nop;
     if (element_ix < my_n_elements) {
-        tag = Annotated_tag(conf.anno_alloc, ref);
+        tag = Annotated_tag(conf.anno_alloc, ref).tag;
     }
     int x0 = 0, y0 = 0, x1 = 0, y1 = 0;
     switch (tag) {
diff --git a/piet-gpu/shader/binning.spv b/piet-gpu/shader/binning.spv
index 6fb185d..96fbcdd 100644
Binary files a/piet-gpu/shader/binning.spv and b/piet-gpu/shader/binning.spv differ
diff --git a/piet-gpu/shader/coarse.comp b/piet-gpu/shader/coarse.comp
index 069367f..332fb48 100644
--- a/piet-gpu/shader/coarse.comp
+++ b/piet-gpu/shader/coarse.comp
@@ -196,7 +196,7 @@ void main() {
         if (th_ix + rd_ix < wr_ix) {
             element_ix = sh_elements[th_ix];
             ref = AnnotatedRef(conf.anno_alloc.offset + element_ix * Annotated_size);
-            tag = Annotated_tag(conf.anno_alloc, ref);
+            tag = Annotated_tag(conf.anno_alloc, ref).tag;
         }
 
         // Bounding box of element in pixel coordinates.
@@ -256,7 +256,7 @@ void main() {
                 }
             }
             AnnotatedRef ref = AnnotatedRef(conf.anno_alloc.offset + sh_elements[el_ix] * Annotated_size);
-            uint tag = Annotated_tag(conf.anno_alloc, ref);
+            uint tag = Annotated_tag(conf.anno_alloc, ref).tag;
             uint seq_ix = ix - (el_ix > 0 ? sh_tile_count[el_ix - 1] : 0);
             uint width = sh_tile_width[el_ix];
             uint x = sh_tile_x0[el_ix] + seq_ix % width;
@@ -305,7 +305,7 @@ void main() {
             // If that turns out to be expensive, maybe we can pack it into
             // shared memory (or perhaps just the tag).
             ref = AnnotatedRef(conf.anno_alloc.offset + element_ix * Annotated_size);
-            tag = Annotated_tag(conf.anno_alloc, ref);
+            tag = Annotated_tag(conf.anno_alloc, ref).tag;
 
             if (clip_zero_depth == 0) {
                 switch (tag) {
diff --git a/piet-gpu/shader/coarse.spv b/piet-gpu/shader/coarse.spv
index 7d0dcce..a7637c6 100644
Binary files a/piet-gpu/shader/coarse.spv and b/piet-gpu/shader/coarse.spv differ
diff --git a/piet-gpu/shader/elements.comp b/piet-gpu/shader/elements.comp
index eb18571..9dc714e 100644
--- a/piet-gpu/shader/elements.comp
+++ b/piet-gpu/shader/elements.comp
@@ -99,7 +99,7 @@ State combine_state(State a, State b) {
 State map_element(ElementRef ref) {
     // TODO: it would *probably* be more efficient to make the memory read patterns less
     // divergent, though it would be more wasted memory.
-    uint tag = Element_tag(ref);
+    uint tag = Element_tag(ref).tag;
     State c;
     c.bbox = vec4(0.0, 0.0, 0.0, 0.0);
     c.mat = vec4(1.0, 0.0, 0.0, 1.0);
@@ -291,7 +291,7 @@ void main() {
         // gains to be had from stashing in shared memory or possibly
         // registers (though register pressure is an issue).
         ElementRef this_ref = Element_index(ref, i);
-        uint tag = Element_tag(this_ref);
+        uint tag = Element_tag(this_ref).tag;
         switch (tag) {
         case Element_FillLine:
         case Element_StrokeLine:
diff --git a/piet-gpu/shader/elements.spv b/piet-gpu/shader/elements.spv
index 2c61b2e..51d3e4c 100644
Binary files a/piet-gpu/shader/elements.spv and b/piet-gpu/shader/elements.spv differ
diff --git a/piet-gpu/shader/kernel4.comp b/piet-gpu/shader/kernel4.comp
index 922ae83..82eb89b 100644
--- a/piet-gpu/shader/kernel4.comp
+++ b/piet-gpu/shader/kernel4.comp
@@ -161,7 +161,7 @@ void main() {
     }
 
     while (true) {
-        uint tag = Cmd_tag(cmd_alloc, cmd_ref);
+        uint tag = Cmd_tag(cmd_alloc, cmd_ref).tag;
         if (tag == Cmd_End) {
             break;
         }
diff --git a/piet-gpu/shader/kernel4.spv b/piet-gpu/shader/kernel4.spv
index 7768659..ebd4811 100644
Binary files a/piet-gpu/shader/kernel4.spv and b/piet-gpu/shader/kernel4.spv differ
diff --git a/piet-gpu/shader/path_coarse.comp b/piet-gpu/shader/path_coarse.comp
index 70251bf..663fe45 100644
--- a/piet-gpu/shader/path_coarse.comp
+++ b/piet-gpu/shader/path_coarse.comp
@@ -96,7 +96,7 @@ void main() {
 
     uint tag = PathSeg_Nop;
     if (element_ix < conf.n_pathseg) {
-        tag = PathSeg_tag(conf.pathseg_alloc, ref);
+        tag = PathSeg_tag(conf.pathseg_alloc, ref).tag;
     }
     switch (tag) {
     case PathSeg_FillCubic:
diff --git a/piet-gpu/shader/path_coarse.spv b/piet-gpu/shader/path_coarse.spv
index d84bd6d..16eb64c 100644
Binary files a/piet-gpu/shader/path_coarse.spv and b/piet-gpu/shader/path_coarse.spv differ
diff --git a/piet-gpu/shader/pathseg.h b/piet-gpu/shader/pathseg.h
index 7c69b9d..f3b2dec 100644
--- a/piet-gpu/shader/pathseg.h
+++ b/piet-gpu/shader/pathseg.h
@@ -54,6 +54,11 @@ PathSegRef PathSeg_index(PathSegRef ref, uint index) {
     return PathSegRef(ref.offset + index * PathSeg_size);
 }
 
+struct PathSegTag {
+   uint tag;
+   uint flags;
+};
+
 PathFillCubic PathFillCubic_read(Alloc a, PathFillCubicRef ref) {
     uint ix = ref.offset >> 2;
     uint raw0 = read_mem(a, ix + 0);
@@ -131,8 +136,9 @@ void PathStrokeCubic_write(Alloc a, PathStrokeCubicRef ref, PathStrokeCubic s) {
     write_mem(a, ix + 11, floatBitsToUint(s.stroke.y));
 }
 
-uint PathSeg_tag(Alloc a, PathSegRef ref) {
-    return read_mem(a, ref.offset >> 2);
+PathSegTag PathSeg_tag(Alloc a, PathSegRef ref) {
+    uint tag_and_flags = read_mem(a, ref.offset >> 2);
+    return PathSegTag(tag_and_flags & 0xffff, tag_and_flags >> 16);
 }
 
 PathFillCubic PathSeg_FillCubic_read(Alloc a, PathSegRef ref) {
diff --git a/piet-gpu/shader/ptcl.h b/piet-gpu/shader/ptcl.h
index 53b9850..0480ad9 100644
--- a/piet-gpu/shader/ptcl.h
+++ b/piet-gpu/shader/ptcl.h
@@ -157,6 +157,11 @@ CmdRef Cmd_index(CmdRef ref, uint index) {
     return CmdRef(ref.offset + index * Cmd_size);
 }
 
+struct CmdTag {
+   uint tag;
+   uint flags;
+};
+
 CmdStroke CmdStroke_read(Alloc a, CmdStrokeRef ref) {
     uint ix = ref.offset >> 2;
     uint raw0 = read_mem(a, ix + 0);
@@ -301,8 +306,9 @@ void CmdJump_write(Alloc a, CmdJumpRef ref, CmdJump s) {
     write_mem(a, ix + 0, s.new_ref);
 }
 
-uint Cmd_tag(Alloc a, CmdRef ref) {
-    return read_mem(a, ref.offset >> 2);
+CmdTag Cmd_tag(Alloc a, CmdRef ref) {
+    uint tag_and_flags = read_mem(a, ref.offset >> 2);
+    return CmdTag(tag_and_flags & 0xffff, tag_and_flags >> 16);
 }
 
 CmdFill Cmd_Fill_read(Alloc a, CmdRef ref) {
diff --git a/piet-gpu/shader/scene.h b/piet-gpu/shader/scene.h
index e6ea591..56c1a86 100644
--- a/piet-gpu/shader/scene.h
+++ b/piet-gpu/shader/scene.h
@@ -160,6 +160,11 @@ ElementRef Element_index(ElementRef ref, uint index) {
     return ElementRef(ref.offset + index * Element_size);
 }
 
+struct ElementTag {
+   uint tag;
+   uint flags;
+};
+
 LineSeg LineSeg_read(LineSegRef ref) {
     uint ix = ref.offset >> 2;
     uint raw0 = scene[ix + 0];
@@ -264,8 +269,9 @@ Clip Clip_read(ClipRef ref) {
     return s;
 }
 
-uint Element_tag(ElementRef ref) {
-    return scene[ref.offset >> 2];
+ElementTag Element_tag(ElementRef ref) {
+    uint tag_and_flags = scene[ref.offset >> 2];
+    return ElementTag(tag_and_flags & 0xffff, tag_and_flags >> 16);
 }
 
 LineSeg Element_StrokeLine_read(ElementRef ref) {
diff --git a/piet-gpu/shader/tile_alloc.comp b/piet-gpu/shader/tile_alloc.comp
index 896bb22..fd89bf7 100644
--- a/piet-gpu/shader/tile_alloc.comp
+++ b/piet-gpu/shader/tile_alloc.comp
@@ -39,7 +39,7 @@ void main() {
 
     uint tag = Annotated_Nop;
     if (element_ix < conf.n_elements) {
-        tag = Annotated_tag(conf.anno_alloc, ref);
+        tag = Annotated_tag(conf.anno_alloc, ref).tag;
     }
     int x0 = 0, y0 = 0, x1 = 0, y1 = 0;
     switch (tag) {
diff --git a/piet-gpu/shader/tile_alloc.spv b/piet-gpu/shader/tile_alloc.spv
index 5fb2a95..66a9fd2 100644
Binary files a/piet-gpu/shader/tile_alloc.spv and b/piet-gpu/shader/tile_alloc.spv differ