Mesh::split_to_u16 now returns a 16-bit indexed Mesh16

CHANGELOG.md

@@ -24,6 +24,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 * `DragValue::range` is now called `clamp_range` and also clamps incoming values.
 * Renamed `Triangles` to `Mesh`.
 * The tesselator now wraps the clip rectangle and mesh in `struct ClippedMesh(Rect, Mesh)`.
+* `Mesh::split_to_u16` now returns a 16-bit indexed `Mesh16`.
 
 ### Fixed 🐛
 

egui_web/src/webgl1.rs

@@ -6,7 +6,7 @@ use {
 
 use egui::{
     math::clamp,
-    paint::{Color32, Mesh, Texture},
+    paint::{Color32, Texture},
     vec2,
 };
 
@@ -265,9 +265,8 @@ impl WebGlPainter {
         }
     }
 
-    fn paint_mesh(&self, mesh: &Mesh) -> Result<(), JsValue> {
+    fn paint_mesh(&self, mesh: &egui::paint::Mesh16) -> Result<(), JsValue> {
         debug_assert!(mesh.is_valid());
-        let indices: Vec<u16> = mesh.indices.iter().map(|idx| *idx as u16).collect();
 
         let mut positions: Vec<f32> = Vec::with_capacity(2 * mesh.vertices.len());
         let mut tex_coords: Vec<f32> = Vec::with_capacity(2 * mesh.vertices.len());
@@ -293,9 +292,9 @@ impl WebGlPainter {
         let indices_memory_buffer = wasm_bindgen::memory()
             .dyn_into::<WebAssembly::Memory>()?
             .buffer();
-        let indices_ptr = indices.as_ptr() as u32 / 2;
+        let indices_ptr = mesh.indices.as_ptr() as u32 / 2;
         let indices_array = js_sys::Int16Array::new(&indices_memory_buffer)
-            .subarray(indices_ptr, indices_ptr + indices.len() as u32);
+            .subarray(indices_ptr, indices_ptr + mesh.indices.len() as u32);
 
         gl.bind_buffer(Gl::ELEMENT_ARRAY_BUFFER, Some(&self.index_buffer));
         gl.buffer_data_with_array_buffer_view(
@@ -379,7 +378,12 @@ impl WebGlPainter {
 
         // --------------------------------------------------------------------
 
-        gl.draw_elements_with_i32(Gl::TRIANGLES, indices.len() as i32, Gl::UNSIGNED_SHORT, 0);
+        gl.draw_elements_with_i32(
+            Gl::TRIANGLES,
+            mesh.indices.len() as i32,
+            Gl::UNSIGNED_SHORT,
+            0,
+        );
 
         Ok(())
     }

egui_web/src/webgl2.rs

@@ -8,7 +8,7 @@ use {
 
 use egui::{
     math::clamp,
-    paint::{Color32, Mesh, Texture},
+    paint::{Color32, Texture},
     vec2,
 };
 
@@ -255,9 +255,8 @@ impl WebGl2Painter {
         }
     }
 
-    fn paint_mesh(&self, mesh: &Mesh) -> Result<(), JsValue> {
+    fn paint_mesh(&self, mesh: &egui::paint::Mesh16) -> Result<(), JsValue> {
         debug_assert!(mesh.is_valid());
-        let indices: Vec<u16> = mesh.indices.iter().map(|idx| *idx as u16).collect();
 
         let mut positions: Vec<f32> = Vec::with_capacity(2 * mesh.vertices.len());
         let mut tex_coords: Vec<f32> = Vec::with_capacity(2 * mesh.vertices.len());
@@ -283,9 +282,9 @@ impl WebGl2Painter {
         let indices_memory_buffer = wasm_bindgen::memory()
             .dyn_into::<WebAssembly::Memory>()?
             .buffer();
-        let indices_ptr = indices.as_ptr() as u32 / 2;
+        let indices_ptr = mesh.indices.as_ptr() as u32 / 2;
         let indices_array = js_sys::Int16Array::new(&indices_memory_buffer)
-            .subarray(indices_ptr, indices_ptr + indices.len() as u32);
+            .subarray(indices_ptr, indices_ptr + mesh.indices.len() as u32);
 
         gl.bind_buffer(Gl::ELEMENT_ARRAY_BUFFER, Some(&self.index_buffer));
         gl.buffer_data_with_array_buffer_view(
@@ -369,7 +368,12 @@ impl WebGl2Painter {
 
         // --------------------------------------------------------------------
 
-        gl.draw_elements_with_i32(Gl::TRIANGLES, indices.len() as i32, Gl::UNSIGNED_SHORT, 0);
+        gl.draw_elements_with_i32(
+            Gl::TRIANGLES,
+            mesh.indices.len() as i32,
+            Gl::UNSIGNED_SHORT,
+            0,
+        );
 
         Ok(())
     }

epaint/src/lib.rs

@@ -57,7 +57,7 @@ mod texture_atlas;
 
 pub use {
     color::{Color32, Rgba},
-    mesh::{Mesh, Vertex},
+    mesh::{Mesh, Mesh16, Vertex},
     shadow::Shadow,
     shape::Shape,
     stats::PaintStats,

epaint/src/mesh.rs

@@ -25,6 +25,8 @@ pub struct Vertex {
 pub struct Mesh {
     /// Draw as triangles (i.e. the length is always multiple of three).
     ///
+    /// If you only support 16-bit indices you can use [`Mesh::split_to_u16`].
+    ///
     /// egui is NOT consistent with what winding order it uses, so turn off backface culling.
     pub indices: Vec<u32>,
 
@@ -51,8 +53,12 @@ impl Mesh {
 
     /// Are all indices within the bounds of the contained vertices?
     pub fn is_valid(&self) -> bool {
+        if self.vertices.len() <= u32::MAX as usize {
             let n = self.vertices.len() as u32;
             self.indices.iter().all(|&i| i < n)
+        } else {
+            false
+        }
     }
 
     pub fn is_empty(&self) -> bool {
@@ -149,13 +155,20 @@ impl Mesh {
 
     /// This is for platforms that only support 16-bit index buffers.
     ///
-    /// Splits this mesh into many smaller meshes (if needed).
-    /// All the returned meshes will have indices that fit into a `u16`.
-    pub fn split_to_u16(self) -> Vec<Mesh> {
+    /// Splits this mesh into many smaller meshes (if needed)
+    /// where the smaller meshes have 16-bit indices.
+    pub fn split_to_u16(self) -> Vec<Mesh16> {
+        debug_assert!(self.is_valid());
+
         const MAX_SIZE: u32 = 1 << 16;
 
         if self.vertices.len() < MAX_SIZE as usize {
-            return vec![self]; // Common-case optimization
+            // Common-case optimization:
+            return vec![Mesh16 {
+                indices: self.indices.iter().map(|&i| i as u16).collect(),
+                vertices: self.vertices,
+                texture_id: self.texture_id,
+            }];
         }
 
         let mut output = vec![];
@@ -190,14 +203,17 @@ impl Mesh {
                 MAX_SIZE
             );
 
-            output.push(Mesh {
+            use std::convert::TryFrom;
+            let mesh = Mesh16 {
                 indices: self.indices[span_start..index_cursor]
                     .iter()
-                    .map(|vi| vi - min_vindex)
+                    .map(|vi| u16::try_from(vi - min_vindex).unwrap())
                     .collect(),
                 vertices: self.vertices[(min_vindex as usize)..=(max_vindex as usize)].to_vec(),
                 texture_id: self.texture_id,
-            });
+            };
+            debug_assert!(mesh.is_valid());
+            output.push(mesh);
         }
         output
     }
@@ -209,3 +225,33 @@ impl Mesh {
         }
     }
 }
+
+// ----------------------------------------------------------------------------
+
+/// A version of [`Mesh`] that uses 16-bit indices.
+///
+/// This is produced by [`Mesh::split_to_u16`] and is meant to be used for legacy render backends.
+pub struct Mesh16 {
+    /// Draw as triangles (i.e. the length is always multiple of three).
+    ///
+    /// egui is NOT consistent with what winding order it uses, so turn off backface culling.
+    pub indices: Vec<u16>,
+
+    /// The vertex data indexed by `indices`.
+    pub vertices: Vec<Vertex>,
+
+    /// The texture to use when drawing these triangles.
+    pub texture_id: TextureId,
+}
+
+impl Mesh16 {
+    /// Are all indices within the bounds of the contained vertices?
+    pub fn is_valid(&self) -> bool {
+        if self.vertices.len() <= u16::MAX as usize {
+            let n = self.vertices.len() as u16;
+            self.indices.iter().all(|&i| i < n)
+        } else {
+            false
+        }
+    }
+}