Parallell tessellation (emilk#3934)

* Part of https://github.com/emilk/egui/issues/1485

This adds a `rayon` feature to `epaint` and `egui` to parallelize
tessellation of large shapes, such as high-resolution plot lines.

crates/egui/Cargo.toml

@@ -66,7 +66,12 @@ persistence = ["serde", "epaint/serde", "ron"]
 ## Enable profiling with the [`puffin`](https://docs.rs/puffin) crate.
 ##
 ## Only enabled on native, because of the low resolution (1ms) of clocks in browsers.
-puffin = ["dep:puffin"]
+puffin = ["dep:puffin", "epaint/puffin"]
+
+## Enable parallel tessellation using [`rayon`](https://docs.rs/rayon).
+##
+## This can help performance for graphics-intense applications.
+rayon = ["epaint/rayon"]
 
 ## Allow serialization using [`serde`](https://docs.rs/serde).
 serde = ["dep:serde", "epaint/serde", "accesskit?/serde"]

crates/egui/src/context.rs

@@ -1977,13 +1977,13 @@ impl Context {
             let paint_stats = PaintStats::from_shapes(&shapes);
             let clipped_primitives = {
                 crate::profile_scope!("tessellator::tessellate_shapes");
-                tessellator::tessellate_shapes(
+                tessellator::Tessellator::new(
                     pixels_per_point,
                     tessellation_options,
                     font_tex_size,
                     prepared_discs,
-                    shapes,
                 )
+                .tessellate_shapes(shapes)
             };
             ctx.paint_stats = paint_stats.with_clipped_primitives(&clipped_primitives);
             clipped_primitives

crates/egui/src/introspection.rs

@@ -146,6 +146,8 @@ impl Widget for &mut epaint::TessellationOptions {
                 debug_ignore_clip_rects,
                 bezier_tolerance,
                 epsilon: _,
+                parallel_tessellation,
+                validate_meshes,
             } = self;
 
             ui.checkbox(feathering, "Feathering (antialias)")
@@ -176,6 +178,12 @@ impl Widget for &mut epaint::TessellationOptions {
                 ui.checkbox(debug_paint_clip_rects, "Paint clip rectangles");
                 ui.checkbox(debug_paint_text_rects, "Paint text bounds");
             });
+
+            ui.add_enabled(epaint::HAS_RAYON, crate::Checkbox::new(parallel_tessellation, "Parallelize tessellation")
+                ).on_hover_text("Only available if epaint was compiled with the rayon feature")
+                .on_disabled_hover_text("epaint was not compiled with the rayon feature");
+
+            ui.checkbox(validate_meshes, "Validate meshes").on_hover_text("Check that incoming meshes are valid, i.e. that all indices are in range, etc.");
         })
         .response
     }

crates/epaint/Cargo.toml

@@ -63,6 +63,16 @@ log = ["dep:log"]
 ## [`mint`](https://docs.rs/mint) enables interoperability with other math libraries such as [`glam`](https://docs.rs/glam) and [`nalgebra`](https://docs.rs/nalgebra).
 mint = ["emath/mint"]
 
+## Enable profiling with the [`puffin`](https://docs.rs/puffin) crate.
+##
+## Only enabled on native, because of the low resolution (1ms) of clocks in browsers.
+puffin = ["dep:puffin"]
+
+## Enable parallel tessellation using [`rayon`](https://docs.rs/rayon).
+##
+## This can help performance for graphics-intense applications.
+rayon = ["dep:rayon"]
+
 ## Allow serialization using [`serde`](https://docs.rs/serde).
 serde = ["dep:serde", "ahash/serde", "emath/serde", "ecolor/serde"]
 
@@ -88,6 +98,8 @@ bytemuck = { version = "1.7.2", optional = true, features = ["derive"] }
 document-features = { version = "0.2", optional = true }
 
 log = { version = "0.4", optional = true, features = ["std"] }
+puffin = { workspace = true, optional = true }
+rayon = { version = "1.7", optional = true }
 
 ## Allow serialization using [`serde`](https://docs.rs/serde) .
 serde = { version = "1", optional = true, features = ["derive", "rc"] }

crates/epaint/benches/benchmark.rs

@@ -60,14 +60,14 @@ fn tessellate_circles(c: &mut Criterion) {
         let prepared_discs = atlas.prepared_discs();
 
         b.iter(|| {
-            let clipped_primitive = tessellate_shapes(
+            let mut tessellator = Tessellator::new(
                 pixels_per_point,
                 options,
                 font_tex_size,
                 prepared_discs.clone(),
-                clipped_shapes.clone(),
             );
-            black_box(clipped_primitive);
+            let clipped_primitives = tessellator.tessellate_shapes(clipped_shapes.clone());
+            black_box(clipped_primitives);
         });
     });
 }

crates/epaint/src/lib.rs

@@ -52,13 +52,16 @@ pub use {
     },
     stats::PaintStats,
     stroke::Stroke,
-    tessellator::{tessellate_shapes, TessellationOptions, Tessellator},
+    tessellator::{TessellationOptions, Tessellator},
     text::{FontFamily, FontId, Fonts, Galley},
     texture_atlas::TextureAtlas,
     texture_handle::TextureHandle,
     textures::TextureManager,
 };
 
+#[allow(deprecated)]
+pub use tessellator::tessellate_shapes;
+
 pub use ecolor::{Color32, Hsva, HsvaGamma, Rgba};
 pub use emath::{pos2, vec2, Pos2, Rect, Vec2};
 
@@ -172,3 +175,38 @@ pub(crate) fn f64_hash<H: std::hash::Hasher>(state: &mut H, f: f64) {
         f.to_bits().hash(state);
     }
 }
+
+// ---------------------------------------------------------------------------
+
+/// Was epaint compiled with the `rayon` feature?
+pub const HAS_RAYON: bool = cfg!(feature = "rayon");
+
+// ---------------------------------------------------------------------------
+
+mod profiling_scopes {
+    #![allow(unused_macros)]
+    #![allow(unused_imports)]
+
+    /// Profiling macro for feature "puffin"
+    macro_rules! profile_function {
+        ($($arg: tt)*) => {
+            #[cfg(feature = "puffin")]
+            #[cfg(not(target_arch = "wasm32"))] // Disabled on web because of the coarse 1ms clock resolution there.
+            puffin::profile_function!($($arg)*);
+        };
+    }
+    pub(crate) use profile_function;
+
+    /// Profiling macro for feature "puffin"
+    macro_rules! profile_scope {
+        ($($arg: tt)*) => {
+            #[cfg(feature = "puffin")]
+            #[cfg(not(target_arch = "wasm32"))] // Disabled on web because of the coarse 1ms clock resolution there.
+            puffin::profile_scope!($($arg)*);
+        };
+    }
+    pub(crate) use profile_scope;
+}
+
+#[allow(unused_imports)]
+pub(crate) use profiling_scopes::*;

crates/epaint/src/mesh.rs

@@ -84,6 +84,8 @@ impl Mesh {
 
     /// Are all indices within the bounds of the contained vertices?
     pub fn is_valid(&self) -> bool {
+        crate::profile_function!();
+
         if let Ok(n) = u32::try_from(self.vertices.len()) {
             self.indices.iter().all(|&i| i < n)
         } else {
@@ -106,6 +108,7 @@ impl Mesh {
 
     /// Append all the indices and vertices of `other` to `self`.
     pub fn append(&mut self, other: Self) {
+        crate::profile_function!();
         crate::epaint_assert!(other.is_valid());
 
         if self.is_empty() {