From efae3860bc3e2197eea39d30d756f93fb14c98d1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?H=C3=A9ctor=20Ram=C3=B3n=20Jim=C3=A9nez?= <hector@hecrj.dev>
Date: Sun, 7 Sep 2025 04:55:45 +0200
Subject: [PATCH] Set `wgpu` viewport and scissoring before `Primitive::draw`

---
 wgpu/src/lib.rs       | 40 ++++++++++++++++++++++++++++++++++++----
 wgpu/src/primitive.rs |  8 ++++----
 2 files changed, 40 insertions(+), 8 deletions(-)

diff --git a/wgpu/src/lib.rs b/wgpu/src/lib.rs
index 3e2e3ea8..3d8ee265 100644
--- a/wgpu/src/lib.rs
+++ b/wgpu/src/lib.rs
@@ -544,22 +544,54 @@ impl Renderer {
                 let mut need_render = Vec::new();
 
                 for instance in &layer.primitives {
+                    let bounds = instance.bounds * scale;
+
                     if let Some(clip_bounds) = (instance.bounds * scale)
                         .intersection(&physical_bounds)
                         .and_then(Rectangle::snap)
                     {
-                        let drawn = instance.primitive.draw(
-                            &primitive_storage,
-                            &mut render_pass,
-                            &clip_bounds,
+                        render_pass.set_viewport(
+                            bounds.x,
+                            bounds.y,
+                            bounds.width,
+                            bounds.height,
+                            0.0,
+                            1.0,
                         );
 
+                        render_pass.set_scissor_rect(
+                            clip_bounds.x,
+                            clip_bounds.y,
+                            clip_bounds.width,
+                            clip_bounds.height,
+                        );
+
+                        let drawn = instance
+                            .primitive
+                            .draw(&primitive_storage, &mut render_pass);
+
                         if !drawn {
                             need_render.push((instance, clip_bounds));
                         }
                     }
                 }
 
+                render_pass.set_viewport(
+                    0.0,
+                    0.0,
+                    viewport.physical_width() as f32,
+                    viewport.physical_height() as f32,
+                    0.0,
+                    1.0,
+                );
+
+                render_pass.set_scissor_rect(
+                    0,
+                    0,
+                    viewport.physical_width(),
+                    viewport.physical_height(),
+                );
+
                 if !need_render.is_empty() {
                     let _ = ManuallyDrop::into_inner(render_pass);
 
diff --git a/wgpu/src/primitive.rs b/wgpu/src/primitive.rs
index b5a73032..dd661e7e 100644
--- a/wgpu/src/primitive.rs
+++ b/wgpu/src/primitive.rs
@@ -48,6 +48,9 @@ pub trait Primitive: Debug + MaybeSend + MaybeSync + 'static {
     /// since reusing the existing render pass should be considerably more
     /// efficient than issuing a new one.
     ///
+    /// The viewport and scissor rect of the render pass provided is set
+    /// to the bounds and clip bounds of the [`Primitive`], respectively.
+    ///
     /// If you have complex composition needs, then you can leverage
     /// [`render`](Self::render) by returning `false` here.
     ///
@@ -56,7 +59,6 @@ pub trait Primitive: Debug + MaybeSend + MaybeSync + 'static {
         &self,
         _renderer: &Self::Renderer,
         _render_pass: &mut wgpu::RenderPass<'_>,
-        _clip_bounds: &Rectangle<u32>,
     ) -> bool {
         false
     }
@@ -93,7 +95,6 @@ pub(crate) trait Stored:
         &self,
         storage: &Storage,
         render_pass: &mut wgpu::RenderPass<'_>,
-        clip_bounds: &Rectangle<u32>,
     ) -> bool;
 
     fn render(
@@ -140,7 +141,6 @@ impl<P: Primitive> Stored for BlackBox<P> {
         &self,
         storage: &Storage,
         render_pass: &mut wgpu::RenderPass<'_>,
-        clip_bounds: &Rectangle<u32>,
     ) -> bool {
         let renderer = storage
             .get::<P>()
@@ -148,7 +148,7 @@ impl<P: Primitive> Stored for BlackBox<P> {
             .downcast_ref::<P::Renderer>()
             .expect("renderer should have the proper type");
 
-        self.primitive.draw(renderer, render_pass, clip_bounds)
+        self.primitive.draw(renderer, render_pass)
     }
 
     fn render(