Erase .fx modification

I know this is more of a shader request, but having taken a look at erase.fx, I thought someone could help me:

What I need is a shader that works like Erase, but instead of taking the alpha channel and erasing with it, I'd like it to take one of the color channels instead.

I need it for pasting transparency into a Canvas, where the opacity would be stored in one of the color channels. I already tried the Grayscale To Opacity shader with Erase on top of it, as well as through an intermediate Canvas, but it didn't work.

Thank you in advance.

erase.fx was done with altered render states. I'm not experienced with it, but here is a list with possible blend modes (explanation of each one further down the page):

D3DBLEND enumeration

Blending is done between source and destination.

Just make sure to omit the suffix D3DBLEND_ and remember case sensitivity. Write them in uppercase as shown in the list. It's trial and error, I'm afraid. Just use combinations for SrcBlend and DestBlend, eg.

SrcBlend = DESTALPHA;

DestBlend = SRCCOLOR;

(don't know if this one makes sense^^)

EDIT: Also have a look at Construct's source code. It seems that only a subset is supported. Common renderer definitions (start at line 156)

It does make perfect sense.

However, blending modes won't help in this case and not because Construct only supports a subset.

It seems that there are none that blend across channels. Alpha only blends with Alpha, R with R etc.

Yet I managed to find a solution - I'm in the process of cannibalizing the Color Mask Effect to do what I require - the logic flow is quite clear and easy to replace with a simple channel shifter - I have the basic operation done, but before releasing, I want to add the following:

-ability to manually select the channel to shift over to alpha

-a choice of either multiplication by the existing alpha or replacement

-an option to inverse the incoming channel

Once done, I'll post it in the Completed addons forum.

Thank you for pointing me in the right direction.