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how to : Bitmap Color Mask
sec_goat
Member #12,838
May 2011

I have a question regarding al_convert_mask_to_alpha. I have managed to open a bitmap in an image editor and get an RGB color to feed into that funciton, but is there some way to make something easier where I do not Have to look up each color for each bitmap?

My idea was this:

al_convert_mask_to_alpha(image, al_get_pixel(image,0,0));

but al_get_pixel does not seem to return an RGB value. What does it return and is it possible to translate it into an RGB value for use in a function like this?

Edgar Reynaldo
Major Reynaldo
May 2007
avatar

If you had read the help pages linked to by your own code tags in your post, you would know al_get_pixel returns an ALLEGRO_COLOR and the second parameter of al_convert_mask_to_alpha takes an ALLEGRO_COLOR. Your code should work as far as I can tell. What isn't working? If you really need the r,g,b,a values, use one of the al_unmap_rgb* functions.

sec_goat
Member #12,838
May 2011

If you had read the help pages linked to by your own code tags in your post

You will have to forgive me, I am coming off Python, which is a little more verbose in the help field. I do now see that at the top of the page it defines return type. I was looking in the text for something that told me return type. I must apologize for my ignorance, also I did not realise that if I post an allegro function it links to the help page, this is an awesome resource. Thank you.

Well it appears the code I wrote up here works exactly correct!
In my actual code I had written it as:

al_convert_mask_to_alpha(player, al_get_pixel(player, al_map_rgb(al_get_pixel(player,0,0)))::)

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