Thank you Alex!
You made my day. Using your suggestion the video is playing more smoothly.
Better than that, I've managed the C library to get the frame data from
OpenCV in BGRA format in order to be able to use the BlExternalForm, but
now I can use directly BGR and save all those alpha bytes.
However, I've noticed that if I try to update my custom Bloc element each
time a new detected frame is available I get an empty window. Only when I
force a small delay (like 5 milliseconds) between frames I can see the
video playing in the window.
An example of the code I'm running on a Playground would be like the
following:
detector := OCVBlobDetector createOn: 0.
aSpace := BlSpace new
extent: 740@580;
title: 'OpenCV Frame'.
aSpace root background: Color gray asBlBackground.
frameElement := (OCVBlocDetectionElement on: detector detect)
relocate: 50@50; yourself.
aSpace root addChild: frameElement.
aSpace show.
detector live: [ :detection |
frameElement detection: detection.
frameElement invalidate.
5 milliSeconds wait.
].
Thank you!
El mié., 12 jun. 2019 a las 20:52, Aliaksei Syrel (<alex.sy...@gmail.com>)
escribió:
> Hi Rafael,
>
> Assuming you have your OpenCV camera frame object named image in BGR
> format (default for OpenCV)
> Here is how you can render it at high fps in Bloc (override *BlElement>>#*
> drawOnSpartaCanvas: aCanvas in a subclass)
>
> surface := aSpartaCanvas bitmap
>
> fromBGR: image imageData
>
> extent: image width @ image height
> stride: image widthStep.
>
>
> aSpartaCanvas fill
>
> paint: surface;
> path: surface bounds;
> draw
>
>
> Cheers,
> Alex
>
>
> On Wed, 12 Jun 2019 at 22:39, Rafael Luque <rafael.luque.le...@gmail.com>
> wrote:
>
>> Hello,
>>
>> I'm experimenting with an integration between OpenCV and Pharo based on
>> uFFI. My native C library opens a video camera and captures frames for
>> detecting certain points (aka blobs) of interest for my use case. The data
>> for these frames are available to Pharo as uchar* inside a C struct.
>>
>> My issues came when I tried to render the video camera frames inside
>> Pharo. The C examples I developed for testing the shared library show
>> frames around 50-60 fps. However, the best I have got in Pharo is around
>> 15-20 fps.
>>
>> My first try consisted of writing an specific ImageReadWriter for the
>> OpenCV image format, so I can build a Form for each frame and render it
>> with Morphic. This way I can render the video camera in GTInspector, but at
>> a terrible 5-10 fps.
>>
>> The second try was to use Bloc to render the Forms. I though the Moz2D
>> backend will provider better performance. Indeed, I got around 15-20 fps,
>> but it is still insufficient for playing video smoothly.
>>
>> My current try consist of using BlExternalForm to avoid all the frame
>> data processing inside Pharo, but I'm finding problems to render this kind
>> of "shallow" Forms using Bloc.
>>
>> I've also find some old mails (2017) about Clément Bera working in games
>> based on Cairo + SDL. Should I explore this approach for video rendering?
>>
>> In summary, I don't know what is the recommended approach (if any) to
>> show a sequence of video frames with decent bit-rate.
>>
>> Thank you!
>>
>
