From 330a4464b112529096578de96e14080ea8e05fa4 Mon Sep 17 00:00:00 2001
From: sjsanc <sjsanc@protonmail.com>
Date: Mon, 13 Apr 2026 17:32:50 +0100
Subject: [PATCH] fix(core): queue pending resize when animationFrame is
 already scheduled to prevent silent drop

---
 .../ContextPoolRenderingEngine.ts             | 17 +++++-
 packages/core/test/RenderingEngineAPI_test.js | 53 +++++++++++++++++++
 2 files changed, 68 insertions(+), 2 deletions(-)

diff --git a/packages/core/src/RenderingEngine/ContextPoolRenderingEngine.ts b/packages/core/src/RenderingEngine/ContextPoolRenderingEngine.ts
index 8df47a5797..77c11ae876 100644
--- a/packages/core/src/RenderingEngine/ContextPoolRenderingEngine.ts
+++ b/packages/core/src/RenderingEngine/ContextPoolRenderingEngine.ts
@@ -33,6 +33,11 @@ import type { VtkOffscreenMultiRenderWindow } from '../types';
  */
 class ContextPoolRenderingEngine extends BaseRenderingEngine {
   private contextPool: WebGLContextPool;
+  private _pendingResizeArgs: {
+    vtkDrivenViewports: (IStackViewport | IVolumeViewport)[];
+    keepCamera: boolean;
+    immediate: boolean;
+  } | null = null;
 
   constructor(id?: string) {
     super(id);
@@ -197,8 +202,8 @@ class ContextPoolRenderingEngine extends BaseRenderingEngine {
    * Only updates the VTK offscreen size when the displayed size (canvas client size in device pixels)
    * differs from the current rendered size (canvas.width/height). The on-screen canvas dimensions
    * are updated only when the VTK render result is copied in _copyToOnscreenCanvas, avoiding
-   * flicker during resize. If a render is already scheduled, resize is deferred until the next
-   * resize() call.
+   * flicker during resize. If a render is already scheduled, the resize is deferred and applied
+   * automatically once the pending frame has been rendered.
    */
   protected _resizeVTKViewports(
     vtkDrivenViewports: (IStackViewport | IVolumeViewport)[],
@@ -236,6 +241,7 @@ class ContextPoolRenderingEngine extends BaseRenderingEngine {
     }
 
     if (this._animationFrameSet) {
+      this._pendingResizeArgs = { vtkDrivenViewports, keepCamera, immediate };
       return;
     }
 
@@ -311,6 +317,13 @@ class ContextPoolRenderingEngine extends BaseRenderingEngine {
     this._animationFrameSet = false;
     this._animationFrameHandle = null;
 
+    if (this._pendingResizeArgs) {
+      const { vtkDrivenViewports, keepCamera, immediate } =
+        this._pendingResizeArgs;
+      this._pendingResizeArgs = null;
+      this._resizeVTKViewports(vtkDrivenViewports, keepCamera, immediate);
+    }
+
     // Trigger all events after rendering is complete
     eventDetails.forEach((eventDetail) => {
       if (eventDetail?.element) {
diff --git a/packages/core/test/RenderingEngineAPI_test.js b/packages/core/test/RenderingEngineAPI_test.js
index 45bf36bd20..a614e29fca 100644
--- a/packages/core/test/RenderingEngineAPI_test.js
+++ b/packages/core/test/RenderingEngineAPI_test.js
@@ -150,4 +150,57 @@ describe('RenderingEngineAPI -- ', () => {
       expect(stackViewports.length).toBe(1);
     });
   });
+
+  describe("RenderingEngine doesn't drop frames", function () {
+    let renderingEngine;
+
+    beforeEach(function () {
+      const testEnv = setupTestEnvironment({
+        renderingEngineId,
+      });
+      renderingEngine = testEnv.renderingEngine;
+    });
+
+    afterEach(function () {
+      cleanupTestEnvironment({
+        renderingEngineId,
+      });
+    });
+
+    it('should update canvas dimensions when resize() is called while a render is pending', function (done) {
+      const element1 = createViewports(renderingEngine, {
+        viewportId: axialViewportId,
+        viewportType: ViewportType.STACK,
+        width: 400,
+        height: 400,
+        useEnableElement: true,
+      });
+
+      const element2 = createViewports(renderingEngine, {
+        viewportId: sagittalViewportId,
+        viewportType: ViewportType.STACK,
+        width: 400,
+        height: 400,
+        useEnableElement: true,
+      });
+
+      renderingEngine.renderViewport(sagittalViewportId);
+
+      element1.style.width = '250px';
+      element1.style.height = '250px';
+
+      renderingEngine.resize(false, true);
+
+      requestAnimationFrame(() => {
+        const viewport1 = renderingEngine.getViewport(axialViewportId);
+        if (!viewport1) {
+          done();
+          return;
+        }
+        expect(viewport1.sWidth).toBe(250);
+        expect(viewport1.sHeight).toBe(250);
+        done();
+      });
+    });
+  });
 });