Firstly your idea although handy won't work for the following reasons.
i) You would have to use a mask with an alpha channel, you cannot use shades of colours fading to black to represent individual masks because of the accuracy of say 8 bits per RGB channel, example (255,128,0) would at some point reach (16,0,0) as it fades to black and would therefore be indestinguishable from a (255,0,0) area. So you would need a seperate alpha channel, or be limited to only having 7 mask colours.
ii) AGS automaticaly assigns walkbehinds to different shades. Ok, that's possible, now suppose you add another walkbehind somewhere in your mask. AGS will now probably automatically assign different values to all the walkbehinds. Great! not. Ok you would need to add a automatic import flag into AGS.
iii) AGS automatically calculates baselines. Fine for the first time you import your background, but you would need to be able to stop it from doing it everytime as you would lose any edits you had made to baselines that were auto generated not where you wanted them. Ok you would need to add a automatic import flag into AGS.
iv) Using the alpha channel in your mask will cause background artifacts to be seen through the characters, as has been amply explained by Snarky, though I don't quite agree with his reasoning, but that might be just me not reading it right, his result is correct.
v) All this can be eliminated by simply using an object with it's own alpha and baseline instead of the walkbehind. If you want to remove the overheads of lots of layers of objects, just cut out the 100% transparent and 0% transparent from the object graphic and use normal walkbehinds to do the job in these areas. I've already used this technique in Bog's Adventures in Underworld with no problems.
vi) 99% of AGS users probably don't even know what an alpha channel is. I think AGS should develop in a way to encourage beginners more and not get itself bogged down in advanced techniques, that can be solved by a little work anyway. But that's maybe a bit off topic.
i) You would have to use a mask with an alpha channel, you cannot use shades of colours fading to black to represent individual masks because of the accuracy of say 8 bits per RGB channel, example (255,128,0) would at some point reach (16,0,0) as it fades to black and would therefore be indestinguishable from a (255,0,0) area. So you would need a seperate alpha channel, or be limited to only having 7 mask colours.
ii) AGS automaticaly assigns walkbehinds to different shades. Ok, that's possible, now suppose you add another walkbehind somewhere in your mask. AGS will now probably automatically assign different values to all the walkbehinds. Great! not. Ok you would need to add a automatic import flag into AGS.
iii) AGS automatically calculates baselines. Fine for the first time you import your background, but you would need to be able to stop it from doing it everytime as you would lose any edits you had made to baselines that were auto generated not where you wanted them. Ok you would need to add a automatic import flag into AGS.
iv) Using the alpha channel in your mask will cause background artifacts to be seen through the characters, as has been amply explained by Snarky, though I don't quite agree with his reasoning, but that might be just me not reading it right, his result is correct.
v) All this can be eliminated by simply using an object with it's own alpha and baseline instead of the walkbehind. If you want to remove the overheads of lots of layers of objects, just cut out the 100% transparent and 0% transparent from the object graphic and use normal walkbehinds to do the job in these areas. I've already used this technique in Bog's Adventures in Underworld with no problems.
vi) 99% of AGS users probably don't even know what an alpha channel is. I think AGS should develop in a way to encourage beginners more and not get itself bogged down in advanced techniques, that can be solved by a little work anyway. But that's maybe a bit off topic.
