Implement MSAA for triangle meshes in iced_glow

glow/src/triangle.rs

@@ -4,6 +4,7 @@ use crate::settings;
 use crate::Transformation;
 use glow::HasContext;
 use iced_graphics::layer;
+use iced_graphics::Size;
 use std::marker::PhantomData;
 
 pub use iced_graphics::triangle::{Mesh2D, Vertex2D};
@@ -18,6 +19,7 @@ pub(crate) struct Pipeline {
     vertices: Buffer<Vertex2D>,
     indices: Buffer<u32>,
     current_transform: Transformation,
+    antialias: Antialias,
 }
 
 impl Pipeline {
@@ -97,6 +99,7 @@ impl Pipeline {
             vertices,
             indices,
             current_transform: Transformation::identity(),
+            antialias: Antialias::new(antialiasing),
         }
     }
 
@@ -157,49 +160,57 @@ impl Pipeline {
             }
         }
 
-        // Then we draw each mesh using offsets
-        let mut last_vertex = 0;
-        let mut last_index = 0;
+        let Self {
+            antialias,
+            current_transform,
+            ..
+        } = self;
 
-        for layer::Mesh {
-            buffers,
-            origin,
-            clip_bounds,
-        } in meshes
-        {
-            let transform =
-                transformation * Transformation::translate(origin.x, origin.y);
+        // Then we draw each mesh using offsets with antialiasing
+        antialias.perform(gl, Size::new(target_width, target_height), |gl| {
+            let mut last_vertex = 0;
+            let mut last_index = 0;
 
-            let clip_bounds = (*clip_bounds * scale_factor).round();
+            for layer::Mesh {
+                buffers,
+                origin,
+                clip_bounds,
+            } in meshes
+            {
+                let transform = transformation
+                    * Transformation::translate(origin.x, origin.y);
 
-            unsafe {
-                if self.current_transform != transform {
-                    let matrix: [f32; 16] = transform.into();
-                    gl.uniform_matrix_4_f32_slice(Some(&0), false, &matrix);
+                let clip_bounds = (*clip_bounds * scale_factor).round();
 
-                    self.current_transform = transform;
+                unsafe {
+                    if *current_transform != transform {
+                        let matrix: [f32; 16] = transform.into();
+                        gl.uniform_matrix_4_f32_slice(Some(&0), false, &matrix);
+
+                        *current_transform = transform;
+                    }
+
+                    gl.scissor(
+                        clip_bounds.x as i32,
+                        (target_height - (clip_bounds.y + clip_bounds.height))
+                            as i32,
+                        clip_bounds.width as i32,
+                        clip_bounds.height as i32,
+                    );
+
+                    gl.draw_elements_base_vertex(
+                        glow::TRIANGLES,
+                        buffers.indices.len() as i32,
+                        glow::UNSIGNED_INT,
+                        (last_index * std::mem::size_of::<u32>()) as i32,
+                        last_vertex as i32,
+                    );
+
+                    last_vertex += buffers.vertices.len();
+                    last_index += buffers.indices.len();
                 }
-
-                gl.scissor(
-                    clip_bounds.x as i32,
-                    (target_height - (clip_bounds.y + clip_bounds.height))
-                        as i32,
-                    clip_bounds.width as i32,
-                    clip_bounds.height as i32,
-                );
-
-                gl.draw_elements_base_vertex(
-                    glow::TRIANGLES,
-                    buffers.indices.len() as i32,
-                    glow::UNSIGNED_INT,
-                    (last_index * std::mem::size_of::<u32>()) as i32,
-                    last_vertex as i32,
-                );
-
-                last_vertex += buffers.vertices.len();
-                last_index += buffers.indices.len();
             }
-        }
+        });
 
         unsafe {
             gl.bind_vertex_array(None);
@@ -279,3 +290,146 @@ impl<T> Buffer<T> {
         }
     }
 }
+
+#[derive(Debug)]
+pub struct Antialias {
+    renderbuffer: Option<Renderbuffer>,
+    sample_count: u32,
+}
+
+impl Antialias {
+    fn new(antialiasing: Option<settings::Antialiasing>) -> Self {
+        Antialias {
+            renderbuffer: None,
+            sample_count: antialiasing
+                .map(settings::Antialiasing::sample_count)
+                .unwrap_or(1),
+        }
+    }
+
+    fn perform(
+        &mut self,
+        gl: &glow::Context,
+        size: Size<u32>,
+        f: impl FnOnce(&glow::Context),
+    ) {
+        if self.sample_count == 1 {
+            return f(gl);
+        }
+
+        let target = glow::DRAW_FRAMEBUFFER;
+
+        let renderbuffer = if let Some(renderbuffer) = self.renderbuffer.take()
+        {
+            if size == renderbuffer.size {
+                renderbuffer
+            } else {
+                renderbuffer.destroy(gl);
+
+                Renderbuffer::new(gl, target, self.sample_count, size)
+            }
+        } else {
+            Renderbuffer::new(gl, target, self.sample_count, size)
+        };
+
+        renderbuffer.bind(gl, target);
+
+        unsafe {
+            gl.clear_color(0.0, 0.0, 0.0, 0.0);
+            gl.clear(glow::COLOR_BUFFER_BIT);
+        }
+
+        f(gl);
+
+        unsafe {
+            gl.bind_framebuffer(target, None);
+            gl.clear_color(1.0, 1.0, 1.0, 1.0);
+        }
+
+        renderbuffer.blit(gl);
+
+        self.renderbuffer = Some(renderbuffer);
+    }
+}
+
+#[derive(Debug)]
+pub struct Renderbuffer {
+    raw: <glow::Context as HasContext>::Renderbuffer,
+    framebuffer: <glow::Context as HasContext>::Framebuffer,
+    size: Size<u32>,
+}
+
+impl Renderbuffer {
+    fn new(
+        gl: &glow::Context,
+        target: u32,
+        sample_count: u32,
+        size: Size<u32>,
+    ) -> Self {
+        let framebuffer = unsafe {
+            gl.create_framebuffer().expect("Create MSAA framebuffer")
+        };
+
+        let raw = unsafe {
+            gl.create_renderbuffer().expect("Create MSAA renderbuffer")
+        };
+
+        unsafe {
+            gl.bind_renderbuffer(glow::RENDERBUFFER, Some(raw));
+            gl.renderbuffer_storage_multisample(
+                glow::RENDERBUFFER,
+                sample_count as i32,
+                glow::SRGB8_ALPHA8,
+                size.width as i32,
+                size.height as i32,
+            );
+
+            gl.bind_framebuffer(target, Some(framebuffer));
+            gl.framebuffer_renderbuffer(
+                target,
+                glow::COLOR_ATTACHMENT0,
+                glow::RENDERBUFFER,
+                Some(raw),
+            );
+            gl.bind_framebuffer(target, None);
+        }
+
+        Self {
+            raw,
+            framebuffer,
+            size,
+        }
+    }
+
+    fn bind(&self, gl: &glow::Context, target: u32) {
+        unsafe {
+            gl.bind_framebuffer(target, Some(self.framebuffer));
+        }
+    }
+
+    fn blit(&self, gl: &glow::Context) {
+        unsafe {
+            self.bind(gl, glow::READ_FRAMEBUFFER);
+
+            gl.blit_framebuffer(
+                0,
+                0,
+                self.size.width as i32,
+                self.size.height as i32,
+                0,
+                0,
+                self.size.width as i32,
+                self.size.height as i32,
+                glow::COLOR_BUFFER_BIT,
+                glow::NEAREST,
+            );
+        }
+    }
+
+    fn destroy(self, gl: &glow::Context) {
+        unsafe {
+            gl.delete_renderbuffer(self.raw);
+            gl.delete_framebuffer(self.framebuffer);
+        }
+    }
+}