From 9d7a8eaedacac2753990b4db90fd930324611d02 Mon Sep 17 00:00:00 2001
From: Alejandro Alonso <alejandroalonsofernandez@gmail.com>
Date: Mon, 15 Jun 2026 10:44:18 +0200
Subject: [PATCH] :bug: Fix rendering artifacts from previous frames

---
 render-wasm/src/render.rs | 20 ++++++++------------
 render-wasm/src/state.rs  |  4 +++-
 2 files changed, 11 insertions(+), 13 deletions(-)

diff --git a/render-wasm/src/render.rs b/render-wasm/src/render.rs
index b613ec5586..8d59339b65 100644
--- a/render-wasm/src/render.rs
+++ b/render-wasm/src/render.rs
@@ -907,6 +907,14 @@ impl RenderState {
 
     pub fn reset_canvas(&mut self) {
         self.surfaces.reset(self.background_color);
+        self.surfaces.clear_backbuffer(self.background_color);
+        self.surfaces.clear_target(self.background_color);
+    }
+
+    /// Drop cached tile textures before a one-shot `render_sync_shape` render.
+    pub fn prepare_sync_shape_render(&mut self) {
+        self.surfaces.clear_tile_atlas();
+        self.surfaces.invalidate_tile_cache();
     }
 
     /// NOTE:
@@ -1085,11 +1093,6 @@ impl RenderState {
         self.include_filter.is_some()
     }
 
-    fn reset_viewer_masked_surfaces(&mut self) {
-        self.surfaces.clear_backbuffer(self.background_color);
-        self.surfaces.clear_tile_atlas();
-    }
-
     /// True when the shape or any descendant is whitelisted.
     pub fn shape_visible_in_include_filter(&self, shape_id: &Uuid, tree: ShapesPoolRef) -> bool {
         let Some(ref include) = self.include_filter else {
@@ -2192,13 +2195,6 @@ impl RenderState {
             self.interactive_target_seeded = false;
         }
 
-        // Viewer fixed-scroll passes reuse the same WASM context; `reset` does not
-        // clear Backbuffer, so pass 2 would otherwise keep pass-1 pixels in regions
-        // that render no shapes for the current mask. Target is cleared in present_frame.
-        if self.viewer_masked_pass() {
-            self.reset_viewer_masked_surfaces();
-        }
-
         let surface_ids = SurfaceId::Strokes as u32
             | SurfaceId::Fills as u32
             | SurfaceId::InnerShadows as u32
diff --git a/render-wasm/src/state.rs b/render-wasm/src/state.rs
index 1995ffe288..9ca681841d 100644
--- a/render-wasm/src/state.rs
+++ b/render-wasm/src/state.rs
@@ -80,7 +80,9 @@ impl State {
     }
 
     pub fn render_sync_shape(&mut self, id: &Uuid, timestamp: i32) -> Result<FrameType> {
-        get_render_state().start_render_loop(Some(id), &self.shapes, timestamp, true)
+        let render_state = get_render_state();
+        render_state.prepare_sync_shape_render();
+        render_state.start_render_loop(Some(id), &self.shapes, timestamp, true)
     }
 
     pub fn render_shape_pixels(