[Kdenlive-devel] Title Widget / Monitor scene speed

[Till Theato]

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On 08/22/2010 03:55 AM, Dan Dennedy wrote:
> On Sat, Aug 21, 2010 at 1:01 PM, Dan Dennedy <dan at dennedy.org> wrote:
>> On Sat, Aug 21, 2010 at 7:30 AM, Till Theato <root at ttill.de> wrote:
> Starting in January 2011 I have the opportunity to write a research
> paper (correct term?) for school. I have been thinking about writing a
>>>
>>> yes, correct term.
>>>
> MLT filter for masking using bezier curves (like masking using a
> polygon) & and a Kdenlive GUI for it. Combined with your idea this would
> be very useful.
>>>
>>> My concept would make "Set mask" be somewhat generic and take any
>>> producer. So, for example, the editor would be a QGraphicsScene, and
>>> Qt can generate SVG Tiny from the drawn shapes via QSvgGenerator paint
>>> device. That SVG would be fed into the MLT qimage producer that is
>>> used by the mask-setter. One could also use a file made in another

While this generally sounds like a good idea if have doubts when it
comes to keyframability. QtSvg as well as MLT would have to support
animated SVG files. And masks without keyframes aren't quite useful for
most cases.
Please correct me if I'm wrong with this.

>>> tool - even a video. (Final Cut lets one drag a file from the clip bin
>>> onto the filter's file widget.)
>>>
>>> Other properties on the mask-setter could use image attributes instead
>>> of a producer - for example, all pixels that fall within a hue range.
>>> Yes, it might be nice if this selection mechanism were extensible
>>> entirely through the other filters, but I think that crosses the line
>>> into the territory of node-editing and my head starts hurting because
>>> I still have to figure out how to integrate the mask with the motion
>>> tracking stuff.
> 
>> Hmm, just playing around with the new Alpha selection effects, and I
>> should add the option to use the alpha channel. Possibly, I could have
>> a mask-define, which will snapshot the alpha and optionally clear it,
>> then allow filters to operate on alpha until a mask-set, then allow
>> filters that apply to primary image channels until mask-apply, which
>> will finally composite the filtered image using the alpha channel over
>> the snapshotted image (in mask-set), and restore the snapshotted
>> alpha, and clear the mask. For example:
> 
>> Levels
>> Mask define
>>     Alpha shapes
>> Mask set (from self or file, using alpha or luma)
>>     3 point balance
>> Mask apply
>> Contrast

So in this way a bezier masking filter could also be used, as I would
have used the alpha channel anyway.
However with everything you wrote I'm not sure if such a filter is
useful at all. With this SVG mask defining thing definitely not.

> 
>>>>>
>>>>> Just some thoughts.
>>>>>
>>>>>> I guess what you mean is that e.g. moving objects has a delay of around 0.2 s?
>>>>>>
> 
> For me the delay is much longer 0.2 s. Maybe around 1s.
>>>
>>> I seem to recall some interesting blog posts on the Nokia Qt site
>>> about QGraphicsScene performance.

Could not find anything that results in a noticeable improvement, but
while testing I figured out that the speed depends on the size. Not the
size of the scene but of the view. So the smaller the monitor, the
better/faster editing geometries works.
I still have no idea what causes this behavior.

regards ttill
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