AGA alpha transparency question

diablothe2nd · 23 July 2013, 19:09

i know that bobs can have a transparent colour, but can they have half transparent colours? for example a shadow used to darken what is behind it on a bob/sprite? or better yet alpha used in a way that removes jaggies and to blend better with the background.

Thorham · 23 July 2013, 19:25

AGA doesn't have alpha transparency so it has to be done in software, and that's going to get slow real quick.

diablothe2nd · 23 July 2013, 19:28

can you fake it?

Thorham · 24 July 2013, 03:55

You can set up the palette (preferably in a 256 color screen) so that certain bit plane combinations show an effect like alpha blending and transparency, but you have to calculate the different combinations of fore and background objects. This limits the number of free colors you have, but it can be fast. Doesn't work for hardware sprites, only for blitter and CPU sprites.

Actually, Diablo 2 uses the palette technique for transparancy in 256 color screens, so it's certainly possible.

Real alpha blending and transparency are, however, still a pain because you 1) have to do the blending/transparency calculations, and 2) you have to do it in HAM, or there's little point.

diablothe2nd · 24 July 2013, 08:42

thanks for the info

pandy71 · 24 July 2013, 14:15

Quote:

Originally Posted by diablothe2nd

can you fake it?

Yep, by pattern for example.

xArtx · 25 July 2013, 15:06

Quote:

Originally Posted by pandy71

Yep, by pattern for example.

Win

23 July 2013, 19:09	#1
diablothe2nd Registered User Join Date: Dec 2011 Location: Northamptonshire, UK Age: 42 Posts: 1,236	AGA alpha transparency question i know that bobs can have a transparent colour, but can they have half transparent colours? for example a shadow used to darken what is behind it on a bob/sprite? or better yet alpha used in a way that removes jaggies and to blend better with the background.

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23 July 2013, 19:25	#2
Thorham Computer Nerd Join Date: Sep 2007 Location: Rotterdam/Netherlands Age: 47 Posts: 3,796	AGA doesn't have alpha transparency so it has to be done in software, and that's going to get slow real quick.

23 July 2013, 19:28	#3
diablothe2nd Registered User Join Date: Dec 2011 Location: Northamptonshire, UK Age: 42 Posts: 1,236	can you fake it?

24 July 2013, 03:55	#4
Thorham Computer Nerd Join Date: Sep 2007 Location: Rotterdam/Netherlands Age: 47 Posts: 3,796	You can set up the palette (preferably in a 256 color screen) so that certain bit plane combinations show an effect like alpha blending and transparency, but you have to calculate the different combinations of fore and background objects. This limits the number of free colors you have, but it can be fast. Doesn't work for hardware sprites, only for blitter and CPU sprites. Actually, Diablo 2 uses the palette technique for transparancy in 256 color screens, so it's certainly possible. Real alpha blending and transparency are, however, still a pain because you 1) have to do the blending/transparency calculations, and 2) you have to do it in HAM, or there's little point.

24 July 2013, 08:42	#5
diablothe2nd Registered User Join Date: Dec 2011 Location: Northamptonshire, UK Age: 42 Posts: 1,236	thanks for the info

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