Can I program a Polygon to filter out colors behind it?

[Analog Being]

I'm making a prism visualizer (like Pink Floyd's Dark Side of the moon; visualized).

It's essentially all completed, but I need to find a way to have the portion of the 'rainbow' coming from inside the prism to be filtered black/white. The portion outside of the prism will remain colored, as they are naturally.

Basically, what I'm looking for is just a triangle 'window' that does nothing but remove color inside, not outside.

Is this possible? I hope I explained this well enough

[Sadler]

Do you mean something like this?

00000000.png (48.04 KiB) Viewed 11120 times

[Analog Being]

Almost. That looks more like a white polygon with some transparency to fade the colors/black; which may actually work.

What I'm trying to achieve (if possible) is a polygon that filters into a monochrome affect.

Preferably, the blacks wont be affected/faded at all, and colors would be a shade of white/gray.

[Sadler]

What I think you need is a weighted monochrome, though this doesn't come with Magic.

Try this: https://editor.isf.video/shaders/5e7a7f ... 18206dde8e

weighted mono - intensity 0.8

00000000.png (17.76 KiB) Viewed 11112 times

[Magic]

Use the HueSaturation module and set the Saturation parameter to -1. This makes the input monochrome.

[Sadler]

ezgif-1-85abbde1c411.gif (390.41 KiB) Viewed 11103 times

[Magic]

Ah yes, I suppose if all the colors are already fully saturated then you'd need that. I was thinking more like this:

Capture.PNG (424.21 KiB) Viewed 11102 times

[Analog Being]

Thank you guys! I love how quickly everyone chimed in to help.

I managed to find another method to do this (before seeing your comments). I'm going to play around now with your other suggestions. I think "my way" may be too resource-intensive.

https://i.imgur.com/zTEUykV.jpg

Eric, I'm really enjoying your visualizers. Thank you for sharing them! I'm having a lot of fun tweaking it