Alpha channel is getting applied twice when drawing to imagematrix

[groovy9]

New to Luxor, I'm doing the following to draw a small blue box and output the top left pixel value. With the blue channel set to 1 and alpha set to 0.5, I expect the pixel I output to have 1.0 blue channel and 0.5 alpha but I'm getting 0.5 for the blue channel, which is effectively doubling the alpha channel effect.

Is there something I'm misunderstanding about how this should work?

using Luxor, Colors, Images

function test()
    w, h = (10, 10)
    m = @imagematrix! zeros(UInt32, h, w) begin
        setcolor((0.0, 0.0, 1.0, 0.5))
        box(Point(0, 0), w, h, :fill)
    end w h
    println(m[1, 1])
end

test()

Ouput:

ARGB32(0.0N0f8, 0.0N0f8, 0.502N0f8, 0.502N0f8)

Expected output:

ARGB32(0.0N0f8, 0.0N0f8, 1.0N0f8, 0.502N0f8)

[groovy9]

I tried some old versions and if you go back far enough, somewhere around 2.4.0, the alpha issue is gone, but only for 1 release, I think. For how, I'm correcting it with this:

# Apply to a color matrix with broadcasting: to_corrected_RGBA.(pixel_matrix)
function to_corrected_RGBA(pixel)
    p = pixel.color
    alpha = UInt8(p >> 24)
    # color correction
    reduction = alpha / 255
    multiple = reduction > 0 ? 1 / reduction : 0
    red = round(UInt8, ((p << 8) >> 24) * multiple)
    green = round(UInt8, ((p << 16) >> 24) * multiple)
    blue = round(UInt8, ((p << 24) >> 24) * multiple)
    (red, green, blue, alpha)
end

[cormullion]

Hi! Thanks for using Luxor!

I seem to remember we had some weird problems with this that I couldn't solve at the time... There's a mention of it in the help text for @imagematrix. Previous issues eg #107 .

I think you can avoid the problem by setting the background with background(0, 0, 0, 1)).

One day someone will find out what's going on! :)