cobalt: Use activity Window surface for UI rendering by kjyoun · Pull Request #11538 · youtube/cobalt

kjyoun · 2026-07-24T16:07:00Z

Introduces support for rendering UI directly into the Activity's Window surface via Window.takeSurface(), as an alternative to an embedded child SurfaceView.

This behavior is abstracted behind WindowSurfaceBridge and is controlled by the --use-window-surface-for-ui command-line flag (disabled by default).

Before
Idx   | Layer Name                                                   | Type             | Z-Ord  | Active Buffer       
-------------------------------------------------------------------------------------------------------------------
1     | dev.cobalt.coat/dev.cobalt.app.MainActivity#0 (Main Window / UI Container) | BufferQueueLayer | 0      | 1920x1080           
2     | SurfaceView - dev.cobalt.coat/dev.cobalt.app.MainActivity#1 (Active UI SurfaceView) | BufferQueueLayer | -1     | 1920x1080           
3     | SurfaceView - dev.cobalt.coat/dev.cobalt.app.MainActivity#0 (Active Video SurfaceView) | BufferQueueLayer | -2     | 3840x2160           
===================================================================================================================

`use-window-surface-for-ui` is enabled
Idx   | Layer Name                                                   | Type             | Z-Ord  | Active Buffer       
-------------------------------------------------------------------------------------------------------------------
1     | dev.cobalt.coat/dev.cobalt.app.MainActivity#0 (Main Window / UI Container) | BufferQueueLayer | 0      | 1920x1080           
2     | SurfaceView - dev.cobalt.coat/dev.cobalt.app.MainActivity#0 (Active Video SurfaceView) | BufferQueueLayer | -2     | 3840x2160           
===================================================================================================================

Issue: 494590075

github-actions · 2026-07-24T16:07:41Z

🤖 Gemini Suggested Commit Message

android: Support Window surface for UI rendering

Enable rendering the UI directly into the Android Activity's Window
surface as an alternative to an embedded child SurfaceView. This allows
Cobalt to take full ownership of the window surface when requested.

This behavior is toggled via a command-line flag and provides better
integration with certain Android window management scenarios where
a separate SurfaceView is not ideal.

Issue: 494590075

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Code Review

This pull request refactors ContentViewRenderView to support rendering directly to the Activity's Window surface via a new WindowSurfaceBridge strategy, alongside the default child SurfaceView rendering path (SurfaceViewBridge). An abstract SurfaceBridge class is introduced to encapsulate these strategies. The feedback highlights a potential NullPointerException in WindowSurfaceBridge.connect() where windowAndroid.getActivity() is dereferenced without a null check.

Introduces support for rendering UI directly into the Activity's Window surface via Window.takeSurface(), as an alternative to an embedded child SurfaceView. This behavior is abstracted behind WindowSurfaceBridge and is controlled by the `--use-window-surface-for-ui` command-line flag (disabled by default). Issue: 494590075

jasonzhangxx

The change overall looks good to me, but we need @johnxwork for a final review.

jasonzhangxx · 2026-07-24T18:28:13Z


    protected SurfaceBridge createSurfaceBridge() {
-        return new SurfaceBridge();
+        if (CommandLine.getInstance().hasSwitch("use-window-surface-for-ui")) {


The function is called very early in CobaltActivity.createContent() right after CommandLine is initialized. My understanding is we have to use kimono gcl to run the experiments. And please double check if the change can be properly enabled via the experiments.

jasonzhangxx · 2026-07-24T18:50:51Z

+                    if (!(surfaceCallback instanceof SurfaceHolder.Callback2)) {
+                        return;
+                    }
+                    ((SurfaceHolder.Callback2) surfaceCallback).surfaceRedrawNeeded(holder);


The input callback is defined as SurfaceHolder.Callback, but takeSurface requires a SurfaceHolder.Callback2. While casting the surfaceCallback to SurfaceHolder.Callback2 is necessary to implement the redraw notification, please ensure that the cast here is intentional and safe.

jasonzhangxx · 2026-07-24T19:00:57Z

-    /**
-     * @return whether the surface view is initialized and ready to render.
-     */
-    public boolean isInitialized() {


nit: this function was removed, but it appears that it was unused anyway.

jasonzhangxx · 2026-07-24T19:07:16Z

+
+        @Override
+        protected void connect(
+                SurfaceHolder.Callback surfaceCallback, WindowAndroid windowAndroid) {


I think adding a new method ContentViewRenderView.getWindow() in ContentViewRenderView and then retrieving the mWindow during the initialize() would be a cleaner, more consistent approach that aligns better with the SurfaceViewBridge initialization pattern.

borongc · 2026-07-24T21:37:49Z

 */
 @JNINamespace("cobalt")
 public class ContentViewRenderView extends FrameLayout {
+    private static final String TAG = "cobalt";


nit: use import static dev.cobalt.util.Log.TAG;

borongc · 2026-07-24T21:54:48Z

+                    mWindowSurfaceHolder = holder;
+                    if (mSurfaceFormat != null) {
+                        Log.i(TAG, "ContentViewRenderView: Applying pending format");
+                        mWindowSurfaceHolder.setFormat(mSurfaceFormat);


Should mSurfaceFormat be cleaned up once it is applied?

borongc · 2026-07-24T21:55:30Z

nit: title should be android: Use activity Window surface for UI rendering

borongc · 2026-07-24T22:00:25Z

-        new CobaltA11yHelper(this, mShellManager.getContentViewRenderView().getSurfaceView());
-
-    maybeRegisterNetworkRecoveryObserver();
+        new CobaltA11yHelper(this, mShellManager.getContentViewRenderView().getAnchorView());


We should check if this breaks a11y.

kjyoun force-pushed the window-surface-pr branch from abfea0c to c37b117 Compare July 24, 2026 16:54

kjyoun marked this pull request as ready for review July 24, 2026 16:55

kjyoun requested a review from a team as a code owner July 24, 2026 16:55

gemini-code-assist Bot reviewed Jul 24, 2026

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Comment thread cobalt/shell/android/java/src/dev/cobalt/shell/ContentViewRenderView.java Outdated

kjyoun force-pushed the window-surface-pr branch from c37b117 to 0e66bb7 Compare July 24, 2026 17:09

kjyoun requested review from borongc, jasonzhangxx and johnxwork July 24, 2026 17:17

jasonzhangxx reviewed Jul 24, 2026

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borongc mentioned this pull request Jul 24, 2026

android: Fix black screen #10765

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borongc reviewed Jul 24, 2026

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cobalt: Use activity Window surface for UI rendering#11538

cobalt: Use activity Window surface for UI rendering#11538
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kjyoun commented Jul 24, 2026 •

edited

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kjyoun commented Jul 24, 2026 •

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