chazbot

Trying to learn about opengl slab processing and hit a snag that I can't seem to find an answer for:

I've got a texture that's being created by a jit.gl.sketch object (via the @capture method). I'm then passing that through some slab objects, and eventually to a jit.gl.videoplane.

One of the slab objs that I need raises the contrast of the texture, and with it, the brightness of its background color. I'd like to make that background transparent.

I think I need to use some kind of luma -> alpha trick, and continue to keep all the work on the GPU w/ a slab object. Any idea how to do this?

Thanks in advance for your help, and please find an example annotated patch attached.

I've got a texture that's being created by a jit.gl.sketch object (via the @capture method).  I'm then passing that through some slab objects, and eventually to a jit.gl.videoplane.

One of the slab objs that I need raises the contrast of the texture, and with it, the brightness of its background color.  I'd like to make that background transparent.

I think I need to use some kind of luma -> alpha trick, and continue to keep all the work on the GPU w/ a slab object.  Any idea how to do this?

creating-an-alpha-channel-w-jit-gl-slab

sounds like you need the ever so useful glclearcolor trick.

basically, you have one gl.sketch that draws all the objects that you want to capture to a texture with alpha (obviously it's capture attribute is set). with a loadbang you send this message to your gl.sketch:

followed by drawobject myobject1, drawobject myobjectn etc.

search the forum for a patch by nesa that shows this trick.

sounds like you need the ever so useful glclearcolor trick.
basically, you have one gl.sketch that draws all the objects that you want to capture to a texture with alpha (obviously it's capture attribute is set).  with a loadbang you send this message to your gl.sketch:

 followed by drawobject myobject1, drawobject myobjectn etc.

You can check the cc.alphaglue.jxs-help.maxpat exemple as a starter .

Creating an alpha channel w/ jit.gl.slab