Video frames display

[Bobsinclare666]

Hi,

I am new in using SFML which I find quite interesting.
I was wondering if someone could confirm that my approach is correct:

I am trying to use SFML as a hardware accelerator to display 2D video frames in a GUI. I have a video camera which triggers a callback every time a new video frame (grey level, 8bpp) is available.

I created a view, an image and a sprite. In the callback, I call the following functions:

Code: [Select]


Image.LoadFromPixels(ImageWidth, ImageHeight, ImageDataPointer);
Sprite.SetImage(Image);
SFMLView.Draw(Sprite);
SFMLView.Display();


Is this the proper (ie. most efficient)way to do this?

Thanks

Bob

[Laurent]

Yes, it is. I'm curious, what kind of framerate do you get with that ?

Note that the ultimate solution would probably be to create your own Drawable object and use an OpenGL dynamic texture (SFML will create a new texture each time you call LoadFromPixels, which is not optimal).

I think I could also add an optimization that would not recreate the texture if the new image has the same dimensions as the old one

[Bobsinclare666]

Merci for the reply Laurent.

The idea is not necessarily to get a high frame rate but rather a low CPU usage at standard frame rates, say 30 fps.

I was not particularly impressed by the solution below, hence my question on whether I was doing things right. NOw that you are telling me that it is creating a new texture everytime, it makes more sense.

Displaying a 512x512 image at 30fps requires something like 40% of my CPU (I have a low profile dual core PC with no special videocard) which is far too much for my need.

Indeed if you could add a way to reuse the same texture, that would be nice. Maybe also adding a way to handle grey level images... I kind of remember that you can use the LUMINANCE type when calling the glTexSubImage2D() function in which case a pointer to a grey level array (ie. not rgba) is fine. I don't know if that is still current or makes sense in this context though.

Best,

Bob

[Laurent]

Indeed if you could add a way to reuse the same texture, that would be nice. Maybe also adding a way to handle grey level images...

Using luminance textures would lower the memory usage, but probably not improve the performances. Unless you have a luminance surface at the source and always need to convert to RGBA, which is very CPU-consuming.

If you can use a profiler (valgrind on Linux) it would be interesting to see where exactly is the CPU bottleneck.

[Laurent]

I've updated sf::Image to reuse the same texture if the dimensions are the same. If you can try the latest sources, tell me if it makes a difference for your app

[Bobsinclare666]

Gee that was fast!
OK I will try asap.
And to reply to your previous question, the below function seems to be the one taking so much time. OK, back to the tests.

Code: [Select]


Image.LoadFromPixels()


[Bobsinclare666]

Hmm.. Which files did you update?
IS it the Windows Development files?

Cheers,

Bob

[Laurent]

No no, I didn't make any new release. To use the latests sources you have to use a SVN client to download and recompile it. It's very easy