This is a great idea. We should just enter a tweak and do it. If the
area that is being cleared is larger than the current size of the
canvas, we can throw away all pending draw commands.
Steve
On 09/08/2013 11:23 AM, Richard Bair wrote:
I mean, it looks like it is working for a few seconds,
but then as the memory fills with the Canvas backlog it can lead to the GC
using a lot more CPU, thus reducing the ability for Canvas to process its
command queue even further, well it just collapses in on itself and dies.
Forking the thread.
The problem with Canvas is that if you have a canvas and you scribble on it,
and then scribble on it some more, and then scribble on it some more, then in
order for us to get the right result in the end, we need to replay all those
scribbles in order. If pulses are not happening, we still need to remember
these scribbles so we can draw the right result.
BUT, if you issue a command to the canvas which will cause it to "clear" all
its contents, then we could throw away any previously buffered data. Right now the only
way to do that would be a fillRect with a solid fill where the fillRect encompasses the
entire canvas area, or a clearRect where the clearRect encompasses the entire canvas area.
This seems like a very simple fix. GraphicsContext.clearRect and GraphicsContext.fillRect should
both (under the right conditions) throw away the previously buffered commands. Then all you have to
do is be sure to make one of these calls (likely just a clearRect) before each frame, and we'll
never buffer more than a single frame's worth of data. We could also add a "clear" method
which is "clearRect(0, 0, w, h)" to make this more foolproof, and then document it as a
best practice to clear the canvas before each rendering if you intend to redraw the entire thing on
each frame.
If you're making use of manually operated "dirty rects" so that you only clear the
damaged area to repaint, then we couldn't employ this technique and we'd have to buffer 'till
kingdom come. So we still need a mechanism exposed in the scene graph of "liveness" and
associated events so that when the scene is no longer live (for example, when minimized) you could
stop your animation timer, but for your specific media use case this isn't as important.
Richard
