Working With Alphas?

Bad answer, but it depends on what you want to do.

Your code there is doing an average. Add four layers and divide by four. So doing an average of the alpha seems to make sense.

What you need is a rule set. Do you want something like Photoshop, where layer order matters? If so, then first you need to do the operations in order.

If what you want is something like Photoshop's multiply layer (where A is the bottom layer and B is the top) then what it does is take pixel color A, multiply it by pixel color B and then call this color Result. Then interpolate between A and Result, using the alpha of layer B.

Well what i basically mean is just layer like photoshop etc would do but without a layer mode applied so basically to put one above the last yet keep a different alpha for each.

So a example would be if i had say a solid red circle over transparent. Doing this as a single thing would be simple and the return for example like -

return r1, g1, b1, circlemask

Then above that a different layer with a solid blue square over transparent that is scaled down to appear within the red circle. As a single thing would be like -

return r2, g2, b2, squaremask

So basically what i would want is to see a solid blue square over a solid red circle with a transparent background. I could easily make 2 separate scripts and blend them as nodes but i want to do it all within 1 basically. The problem is i can't figure it out to get these results as it's like how you say i am getting some sort of average like you suggest using code like i posted before and it effects the colors with any maths i try. I am guessing if it's possible i am just not sure on the maths needed to mix between them yet, what mike suggests seems like the thing needed but i am not sure about the correct code to do it.

Reading what Vladimir just said though it seems blending/layering above the last is not possible right now?

Maybe if it is possible someone could post a basic example of stacking 4 layers each with a input and alpha input or something as that would show me exactly what i need i am guessing. Thanks for the help everyone

This code seems to work well and shows the method for Alpha compositing i needed. Thanks Sphinx

Edit -

By the way talking about optimizations i am just wondering how optimized is Lua in comparison to standard nodes? Would rendering times be cut when using lua code if it replaced a task needing many standard nodes or does it have not much effect on the time it takes to render?

Quote
Generally, standard components are much faster, but connections between them introduce a slight overhead. It is difficult to say which approach would work better -- it heavily depends on the task.

Indeed! For my test case (mixed alphas and opacity), native blend rendered at 0.17 secs and the above function rendered at 0.72 secs.

I tried optimizing a few bits here and there, but the lua parser seem to do some tricks by its own.. I only managed to tweak out a few milisecs.

Here is the "optimized" version:

Quote

function get_sample(x, y) -- fetch inputs local O = get_sample_grayscale(x, y, OPACITY) if O > 0 then local Ra, Ga, Ba, Aa = get_sample_map(x, y, FOREGROUND) -- combine foreground alpha and master opacity Aa = O * Aa if Aa > 0 then if Aa < 1 then local Rb, Gb, Bb, Ab = get_sample_map(x, y, BACKGROUND) if Ab > 0 then if Ab < 1 then -- blend individual channels local Ao = Aa + Ab * (1 - Aa) local R_Ao = 1 / Ao Ab = Ab * (1 - Aa) * R_Ao Aa = Aa * R_Ao return Ra * Aa + (Rb * Ab), Ga * Aa + (Gb * Ab), Ba * Aa + (Bb * Ab), Ao else return Rb + (Ra - Rb) * Aa, Gb + (Ga - Gb) * Aa, Bb + (Ba - Bb) * Aa, 1 end else return Ra, Ga, Ba, Aa end else return Ra, Ga, Ba, Aa end else return get_sample_map(x, y, BACKGROUND) end else return get_sample_map(x, y, BACKGROUND) end end;