Moving lines causes rendering to flash

[meganrogge]

Testing #253007

Holding down option/alt and pressing up/down arrow keys, I see rendering flashes

moving-lines.mov

[aiday-mar]

Hi thanks for filing this issue. I have investigated this issue and I think I know why this happens. When you move a line up or down, we first delete the line that needs to be moved and then add it at the right location in a second step. The typescript service client host takes a bit of time to recalculate the outline model which is why you see this flickering because the decoration update is not done instantaneously. The speed of update is dependent here on the speed of the calculation of the outline model. I am not sure how to fix this easily. One fix would be to define an operation that moves a line to a different location and carries over the decoration of that line instead of deleting them. I marked this issue as being under discussion because it's not clear yet if and how this should be fixed. I hope that when variable font sizes are used in practise, the decorations will be updated sufficiently quickly so as to not see the flickering.