readback from gpu just for a 0 or 1?


    Feb 20 2013 | 11:14 pm
    i am wondering...:
    i have a vast chain of slabs doing all sorts of complicated things very nicely... but now i need to know just wether the luminance of one of these textures in between is above or below a certain threshhold. i searched for quite a bit but it seems i really have to readback to cpu for this... do i?
    i attached what i currently do below... as soon as i connect it, i get a 20 fps framedrop - even with this tiny texture.
    if i really have to read back, can this been done more efficiently?
    thanks!
    k

    • Feb 21 2013 | 9:08 pm
      don't bother - i solved this for the time being by grabbing the signal before loading it on the gpu and then recreating the whole slabchain in cpu-land. not pretty but since i can work with a tiny, tiny matrix it does not affect performance...
      k
    • Mar 14 2013 | 12:08 am
      some last remark on this if someone else should stumble across this problem: i did not try this in any way but i am just browsing through the filters of jit.gl.imageunit ( https://developer.apple.com/library/mac/#documentation/GraphicsImaging/Reference/CoreImageFilterReference/Reference/reference.html ) and there are a bunch of filters which return culminated values as single pixels which could probably be helpful with this sort of stuff... to get a value (not a pixel) you would still need to readback though.
      k