Selection highlighting smudges canvas while animating

[vpanichkin]

Version

4.5.1

Test Case

http://jsfiddle.net/m0jpr3Ld/

Information about environment

Chrome 91.0.4472.114

Steps to reproduce

1. Double click on the word "text" to select it
2. If the word it selected, the text will move to the top

Expected Behavior

Selection highlighting does not smudge the canvas

Actual Behavior

Selection highlighting is drawn "a path" while animation

P.S. Same happens with a cursor

[avra-m3]

Looks like the root cause is IText.clearContextTop only clears the area inside of the text box, a little bit of whatever is drawn gets left behind if the object moves before the next render cycle.

Would it be safe to clear the entire top context? Or would the preferred option be to store the last known coords of a selection/cursor during the render cycle and clear that area next time around.

I'd love to help out and this seems like a straightforward bug to dip my toes into, would love to hear what the preferred approach would be.

[asturur]

Yes, this was thought as an optimization.... because text isn't supposed to move while editing, and on large canvases, for some reason, this gets slow.
It does create issues tho, and we should probably remove this feature.

[asturur]

Alternatively is maybe possible to do a better sync of the request animation frame with the current object position

[avra-m3]

I'll take a shot at option #2 and raise a pr when it's done. ☺️

[asturur]

yes please! if you have questions ask

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[avra-m3]

I've put some thought into it and would it be practical for animate to have a beforeChange event? This would allow us to clear context top before the transformation matrix changes.

Thanks @asturur, sorry for the delay getting back to this ☺️

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.