Re: [9fans] vncv sw cursor trail

["Ярослав Коломієць" <yarikos@gmail.com>]

> the issue, and this fact this fix works must mean that
> devdraw(3)'s 'd' command usually doesn't cause (much)
> cursor flicker, but the 'y' command does.
> 
> so either there is a timing or locking problem on the pi,
> or swcursoravoid(r) is not called for the 'y' command.

Correct: swcursoravoid is called from hwdraw; memdraw (the 'd' case) does call hwdraw, memload (the 'y' case) does not.
Other programs avoid the issue because the programs do not load images directly to screen.

I guess what happens is the cursor draw scheduled after swcursoravoid saves part of the remote cursor image which is being drawn in meantime.
This is yet to be verified.

> (and allocating new images might amplify latency.)

The potential latency hit could be avoided by pre-allocating an offscreen storage big enough (double-buffering); this would cost more kernel draw memory though.
So until latecy suffers in practice the cost doesn't worth paying.

Yaroslav