Hello there,

Kudos to @cuinjune for the awesome Ofelia and to @60hz for the brilliant work with the fast prototyping - those abstractions are a great entry point for me. It's really exciting stuff, but I'm afraid I'm floundering around a bit. My question is as above - I'm hoping I can find a green screen solution - perhaps along the lines of

ofxChromaKeyShader
https://github.com/musiko/ofxChromaKeyShader

but I need help to make the jump with this into Ofelia.

Any pointers or links?

@Tractor

I don't have anything working right now, but:

https://github.com/jamshark70/Ofelia-Fast-Prototyping/commits/topic/shader-support

This is a fork off of 60Hz's abstractions, including an (experimental) [of.shader] object.

I think a green screen would be pretty easy to write as a fragment shader, and this would hook it in.

hjh

Much appreciated @ddw_music. I'll riddle this and see how far I get on the learning curve... meanwhile if there are any further suggestions out there I'll be very grateful...

I just had another quick look at this.

A green screen requires two input images. Currently [of.shader] doesn't support that... and it would be difficult to disambiguate which image is which.

Needs a bit more thought.

hjh

Actually -- a Processing example suggests that the shader doesn't need two image inputs. All you really need to do is draw two layers: 1, a background layer, and 2, use the shader to generate alpha on the foreground layer, and draw on top of the background.

That can be done with the work that I did on shaders before.

I had a crack at it, and I'm afraid I got only as far as not crashing. This is probably because I don't understand the math that's being done on the pixel colors, and didn't take time to figure it out. (Most of the fragment shader is copied directly from Processing example.)

You would need the shader-support branch of my fork of 60Hz's abstractions: https://github.com/jamshark70/Ofelia-Fast-Prototyping/tree/topic/shader-support -- don't use the main branch! This is all still experimental and not ready to merge.

Then the foreground layer looks like this (haven't added background yet): 0801-chromakey-test.pd

The problem at this point is that I can't find HSV settings to make the green bits actually transparent. I would have expected that setting the range slider to 1.0 would make everything transparent, but it isn't even doing that. So there must be a logic error in the fragment shader, but I'm out of time for now. Maybe you can figure it out.

At least -- having a template that doesn't crash is a good step forward.

hjh

This is very generous of you @ddw_music, thank you so much for your time and thought with this. This looks exciting, I must go set up your fork of the abstractions and see what I can learn. I'm afraid however my coding chops need major upping, but I'll certainly keep you posted on any progress. Again, much appreciated.

@Tractor

Unfortunately, I found later that my fork of the 60hz abstractions breaks drawing order, so the transparency doesn't work.

I'm afraid I have to give up on the project entirely. I won't have time.

But you should be able to take those GLSL files and load them with your own Lua code in an ofelia object. GLSL is separate; there's no tight coupling between my [of.shader] abstraction and the shader implementation.

hjh

@ddw_music
Understood. I'm grateful for the starting point though. It's all learning for me, in any case, so I'll keep at it and see what I can come up with. Respect.