[vlc-devel] [PATCH] window: add an API to show or hide the cursor over the window

[Steve Lhomme]

On 4/5/2019 8:38 AM, Rémi Denis-Courmont wrote:
> This was removed on purpose for reasons already outlined. I don't 
> think it should be added back.

OK, I think you're referring to https://trac.videolan.org/vlc/ticket/18661

I don't like duplicated (many times) code but in this case it kinda 
makes sense. Showing the mouse has to be done ASAP when the mouse starts 
moving again. I'm not sure the delay going through the core is that big 
though. When the mouse moves or buttons are clicked the vout_window_t  
reports it (to the core). This is done synchronously.  In would call 
vout_window_ShowCursor(true) right away, also synchronously. This is 
exactly the same as when it's handled internally.

The timer to hide the mouse is a different story. It can tick in another 
thread then the vout_window_ShowCursor(false) has to be sent 
asynchronously to the UI thread. While the message is pending to be 
treated the mouse could move and vout_window_ShowCursor(true) would then 
be called and be treated synchronously. The "false" state will be 
received after that.

That's the case where the .show_cursor() callback sets the cursor state 
right away. But if we say that the callback can be sent from any thread, 
it's the responsibility of the receiver to forward it properly to its UI 
thread (if any). For example using an atomic bool to keep the latest 
state and sending a message to the UI thread. But in that case the 
cursor showing would not be done ASAP and would be treated possibly 
after a lot of other messages to the UI thread, maybe even some paint 
messages.

So it's a pity we have to duplicate the code but I don't see another way.