_onDraw() performs heavy blocking operations on the UI thread (severe jank & ANR risk)

[nbd-boss]

Hello, I found that _onDraw() inside BRouterMapView performs a large amount of heavy work directly on the UI thread, including:

● Calling Thread.sleep() inside UI rendering (200–500ms)

● Creating a large Bitmap every frame

● Filling large pixel arrays

● Iterating over large sets (openSet, nogoList, wpList)

● Running business logic inside onDraw

● Triggering invalidate() every frame → infinite redraw loop

These behaviors may cause:

• Long UI thread blocking
• Extremely low frame rate
• Frozen UI / unresponsive touch events
• High CPU load
• Potential ANR on many devices

According to Android guidelines, onDraw() must stay lightweight and should not contain:

• Sleeping
• Heavy CPU operations
• Bitmap allocation
• Business logic
• Infinite redraw loops

Suggestions:

1. Move all routing calculations and pixel generation to a background thread
2. Keep onDraw() strictly for drawing only
3. Pass results from worker threads to the View
4. Only draw already-prepared bitmap on UI to avoid blocking

This is a structural issue, and fixing it would significantly improve UI responsiveness and stability.

Thank you.

[polyscias]

This is the repository for the Brouter java app, for brouter-web issues see:

https://github.com/nrenner/brouter-web/issues/

and please close this issue.

Edit: Incorrect comment.

[afischerdev]

@polyscias
I'm sorry to say that, this is our point and has nothing to do with the BRouter web.
Please see here

[EssBee59]

I'm sorry to say that, this is our point and has nothing to do with the BRouter web.

I agree, it has noting to do with brouter-web!
On the other side, "ondraw" suggests, it has to do with maps viewing?
I am not expert in that area, but I think, this is part of the foreground-ground app, that mean "setup"?

If so, I would not longer consider the risk of blocking operation: (as it is only used for very short slots)
The defect /request should be (by need) addressed to the navigation apps, that are using the Brouter in background (Osmand, etc...).
Only the navigation apps are using the "ondraw" intensively

[afischerdev]

@EssBee59

Only the navigation apps are using the "ondraw" intensively

That is correct but that's not our business. The announced problems are BRouter problems.
When you do a longer route in your favorite navigator and then open the BRouter app, you will find the option to repeat last route calculation and this starts a beautiful animation over the points BRouter uses.

This is not a pressing problem but it should be done some day.