Quartz Compositions with Isadora Add alpha Actor

  • Hello everyone!

    I'm just starting to get to grips with some of the awesome potential Quartz Composer has to offer, and really enjoying the publishable inputs through to Isadora.

    I've just whipped up a really nice fire particle generator in QC, and have successfully loaded it up in Isadora.

    Now, I'm keen to be able to use this as part of a video feed amalgamation.
    (For instance, if using a standard Isadora set up, I'd use the add alpha channel, I wish to achieve a similar effect)

    While i know there's a CI video in watcher, and am able to connect it to the CI projector, my efforts to amalgamate the images (aside from a boring overlay) have been in vain.

    Could someone offer me some advice?

  • Dear Ed,

    Well, the first bit of advice is to avoid the Image to Video actor. While that would allow you to combine the image with the old, CPU based actors, you get a performance hit any time you try to bring images from the GPU (Core Image) into the CPU (old style Isadora.)
    You want to stay within the realm of CI for best performance. In your case, I'd look at the CI Blend With Alpha Mask, which is documented (along with Apple's other CI Plugins) [on this page](https://developer.apple.com/library/mac/documentation/GraphicsImaging/Reference/CoreImageFilterReference/index.html#//apple_ref/doc/filter/ci/CIBlendWithAlphaMask).
    Take note that the mask input of  CI Blend With Alpha Mask pays attention to the incoming images _alpha_ channel value, not color of the image itself.

  • Dear Mark,

    Thank you very much for such an informative and clear response.

    I'm just starting to get to grips with vast array of actors CI has to offer.