RFR: 8335748: Rippling of frame on scrolling

[Ambarish Rapte]

On Mon, 24 Nov 2025 11:54:26 GMT, Lukasz Kostyra <lkostyra at openjdk.org> wrote:

>> **Issue:** 
>> With metal pipeline, frame tearing is observed when scrolling the content. Perform small fling gesture scrolls for observing the issue, the issue occurs/observed easily when scroll is coming to and end.
>> 
>> **Cause:**
>> vsync is not enabled for metal pipeline.
>> 
>> **Fix:** 
>> 1. Enable vsync for metal pipeline. The vsync shall be enabled by default. It can be disabled with `-Djavafx.animation.fullspeed=true`.
>> 2. Synchronize the access to offline render target texture.
>> 2.1 The `GlassMTLFrameBufferObject._texture` object is created and destroyed by **QuantumRenderer** thread, and
>> 2.2 `GlassMTLFrameBufferObject._texture` is also accessed on **Appkit** thread through function `GlassLayerMTL.blitToScreen()`
>> 2.3 NSLock is created to synchronize the acess
>> 2.4 Without this synchronization, a crash could occur in scenario when JavaFX app window is moved between screens that differ in refresh rate.
>> 
>> **Verification:**
>> 1. Test that no frame tearing is observed, when scrolling(easy to test with small fling scrolls)
>> 2. Test no issue observed when moving window among screens.
>> 3. General sanity testing of UI.
>> 
>> **Test:**
>> A unit or system test is not possible for this scenario.
>
> modules/javafx.graphics/src/main/native-glass/mac/GlassLayerMTL.m line 155:
> 
>> 153:     // {
>> 154:     //     The texture is locked, either being created/destroyed or being encoded into BlitEncoder
>> 155:     //     hence the frame could be dropped.
> 
> Just a curiosity question, but would we have a possibility to wait for the texture to become available to us instead of dropping the frame?

Waiting could cause a crash, in situation when the lock is already acquired for destroying / creating the texture.
In that case the size of current CAMetalDrawable and size of newly created texture could mismatch.

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PR Review Comment: https://git.openjdk.org/jfx/pull/1978#discussion_r2558702078