From b62aed86f920860030db10e0841524691a99cdc9 Mon Sep 17 00:00:00 2001
From: Haroon Qureshi <haroonq@google.com>
Date: Thu, 12 Mar 2026 04:56:10 -0700
Subject: [PATCH] Recreate swap chain when the window size changes.

PiperOrigin-RevId: 882521107
Change-Id: I0d29d2e323e7830256c24eead439b3f2eb55de40
---
 .../filament/filament/filament_context.cc           | 13 +++++++++++++
 .../filament/filament/filament_context.h            |  2 ++
 2 files changed, 15 insertions(+)

diff --git a/src/experimental/filament/filament/filament_context.cc b/src/experimental/filament/filament/filament_context.cc
index 844d3cf1..e514e1d7 100644
--- a/src/experimental/filament/filament/filament_context.cc
+++ b/src/experimental/filament/filament/filament_context.cc
@@ -140,6 +140,19 @@ void FilamentContext::Render(const mjrRect& viewport, const mjvScene* scene,
     mju_error("Unexpected context.");
   }
 
+  // If we're rendering to the window, and the window size has changed, we need
+  // to reacquire the swap chain.
+  if (scene_swap_chain_target_ == kWindowSwapChain &&
+      (viewport.width != window_width_ || viewport.height != window_height_)) {
+    if (window_width_ != 0 && window_height_ != 0) {
+      engine_->flushAndWait();
+      engine_->destroy(window_swap_chain_);
+      window_swap_chain_ = engine_->createSwapChain(config_.native_window);
+    }
+    window_width_ = viewport.width;
+    window_height_ = viewport.height;
+  }
+
   scene_view_->SetViewport(viewport);
   scene_view_->UpdateScene(con, scene);
   // Update the UX renderable entity after processing the scene in case there
diff --git a/src/experimental/filament/filament/filament_context.h b/src/experimental/filament/filament/filament_context.h
index dc460d9f..d0e7a75e 100644
--- a/src/experimental/filament/filament/filament_context.h
+++ b/src/experimental/filament/filament/filament_context.h
@@ -89,6 +89,8 @@ class FilamentContext {
   std::unique_ptr<ObjectManager> object_manager_;
   std::unique_ptr<SceneView> scene_view_;
   std::unique_ptr<GuiView> gui_view_;
+  int window_width_ = 0;
+  int window_height_ = 0;
 };
 
 }  // namespace mujoco