API Review RT:17407 Canvas Node

Jim Graham james.graham at oracle.com
Wed Apr 25 11:23:23 PDT 2012

Right now when you draw it has to be on the thread on which you respond 
to inputs or do other SG modifications.  In other words, any thread 
where you can appropriately call cv.setWidth(), group.add(cv), etc. is a 
thread you can render on.  The rendering is "remembered" in a buffer and 
it isn't actually drawn until the render pass.  At that point we simply 
eat the buffer and render it in a tight loop so any pauses for thought 
in your rendering code would only affect the event and SG modification 
threads, not the render thread.  (The pauses aren't stored in the buffer. ;)

We looked at ways of relaxing that further, but they won't come in this 
first round of the API.  It would necessitate having multiple HW 
contexts and have a context set aside to only be used for Canvas 
rendering into its texture with a clearly defined buffer swap that has 
to be synchronized across the threads.  Unfortunately that model is not 
easy to support with D3D, our most common hw solution, so it is still 
just a pet theory...


On 4/25/12 1:38 AM, Dr. Michael Paus wrote:
> Am 25.04.2012 10:03, schrieb Jim Graham:
>> Hmmm... More variants of Canvas or more attributes to set...?
> I was just thinking about potential use-cases for the canvas node and
> stumbled over the
> following question. How can I still provide a super-smooth GUI if I have
> a canvas drawing
> which lasts longer than the interval between two pulses. Maybe it even
> lasts more than
> a second. My understanding of the current canvas design proposal is that
> when I redraw
> the canvas, for whatever reason, the GUI is basically blocked for this
> time. Is that true?
> If the above interpretation is right I would like to propose a
> modification of the design
> which makes it possible to have a double buffer canvas where the
> currently active
> buffer is redrawn whenever the JavaFX runtime needs to redraw the node
> and where
> I can render into the second buffer from ANY thread at any time without
> disturbing the
> smoothness of the GUI. When I am done with the rendering I just signal a
> buffer switch
> and with the next pulse the new buffer is shown.
> What do you think?
> Michael

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