Composer : LUT pass breaks transparency

Questions
#1

Hi all,
I followed the tutorial here:

But I wanted to modify it so that the background is NOT included in the LUT effect.
So I put it in the CSS.
But the alpha doesn’t seem to work and I have a black background.
I made a codepen here:

Note: if I comment line 169 (“composer.addPass(effectLUT)”), the alpha works and I see my background. But then when I choose a LUT in the menu (for example “identity no filter”) the background goes black.

#2

The example samples from a LUT which has no transparency by default. Meaning the alpha values will always be 1. You can restore the original alpha by adding the following line at the end of your fragment shader:

gl_FragColor.a = originalColor.a;
#3

updated my codepen… It works!
thanks man!