IssueTracker

Component used:

CanvasFrontBufferedRenderer

Version used:

androidx.graphics:graphics-core:1.0.2

Devices/Android versions reproduced on:

We tested and made the recording with Samsung Galaxy Tab S9 FE.

Meanwhile, we notice that the issue predominantly occurs on low-end devices. Our users have also reported experiencing this problem on devices such as the Samsung Galaxy Tab S9 FE+, Samsung Galaxy Tab S6 Lite and Samsung Galaxy Tab A9.

Sample project:

https://github.com/nightism/AndroidLowLatencyMemoryLeakSample/tree/main/StylusLowLatency

This project is modified based on the Android official input samples demo project here.

Issue description:

In the attached recording, you can observe that when the navigation bar is hidden, the strokes created by each touch are not rendered on the screen in real-time. Initially, only the first few strokes are visible, and subsequent strokes do not appear until the pen is lifted. Interestingly, this issue does not occur when the navigation bar is displayed or when screen recording is enabled.

The navigation bar's visibility is controlled by these code lines.

The file CanvasLowLatencyRenderer.kt is responsible for creating and drawing the lines. The function onDrawFrontBufferedLayer is directly associated with the canvas drawing logic during motion.

In Android's original example, onDrawFrontBufferedLayer allocated a bitmap and triggered software rendering while drawing the front buffer in the render thread to clear prediction lines. In our implementation, this has been optimized with canvas.drawRect, yet the stroke rendering issue persists.

Furthermore, even when we completely bypass the logic for clearing prediction lines by commenting out the relevant code (these lines) related to scissor box clearing and damaged area re-drawing, the issue remains unresolved.

Screen recording explanation:

• [00:04 - 00:07] Drawing with the navigation bar displayed: Drawing is fluid with no issues.
• [00:08 - 00:14] Hide the navigation bar and attempt to draw: Only the initial strokes are visible; subsequent strokes do not appear until the stylus is lifted.
• [00:15 - 00:20] With the navigation bar displayed again: Drawing is smooth with no issues.
• [00:21 - 00:25] With the navigation bar hidden again: Drawing is lagged; strokes are not visible until the stylus is lifted.
• [00:30 - 00:41] With screen recording turned on and the navigation bar displayed: Drawing is smooth with no issues.
• [00:42 - 00:49] With screen recording turned on and the navigation bar hidden: Drawing is smooth with no issues.
• [00:50 - 00:58] With screen recording turned off and the navigation bar hidden: Drawing becomes lagged again; strokes are not visible until the stylus is lifted.