Handle Alpha band

[nicastel]

Handle alpha band via "ETC1(RGB)+ETC1(ALPHA)" as adobe did in ATF : http://wiki.starling-framework.org/manual/atf_textures#creating_an_atf_texture

[nicastel]

Some ideas about how to handle it after compression :
http://malideveloper.arm.com/develop-for-mali/sample-code/etcv1-texture-compression-and-alpha-channels/

METHOD 1&2 are basically the same from a file point of view (2 series of bit compressed with ETC1) so my priority is to support this one.

[frmz]

It would be nice to have a quick way to understand if this is needed starting from a Bitmap, i mean, given an Image its not very easy to understand if that Bitmap has an used alpha channel and thus require alpha or if the alpha channel is not used.

[ndorigatti]

hello @frmz , as far as I know there is no fast and easy way to understand if the alpha channel of an image is not used. In android bitmaps can have different configurations, so if the bitmap is for example RGB_565 for sure there is no alpha.
But if the bitmap is ARGB_8888 the only way you have is to check pixel by pixel...
there are some tricks, but maybe only for PNGs or with specific code...
http://stackoverflow.com/questions/12080083/check-transparency-existence-load-only-rgb-values

[frmz]

@ndorigatti suprisingly i have found that Bitmap.hasAlpha() method actually works, probably it keeps track of this natively while Bitmap is in use (off course you need to have an ARGB_8888 bitmap fully loaded first, so, memory wise, might not be good for everyone), i am going to try to use ETC1 only in that case and create it on the fly using this lib, hope it will work, i am really surprised that this repo didnt get much attention, i think using RS is really a veryvery good idea

[ndorigatti]

@frmz does it works really? Does it tell you if there is at least one pixel with alpha? This is good (and hopefully working for every android version).
Yes, RS is really fast at doing this and since now minsdk is 14-15 (does somebody really care about gingerbread?! :D) i think it should be used for this task!

[frmz]

@ndorigatti yeah, well, on my tests it works, my min sdk is 19 with GLES 3 so i would really love to see this ported to ETC2 also since most of my users have it, i saw that there is a bug request for this on the Android bugtracker hope it will be solved soon.

[ndorigatti]

I don't know about gls3 but I'm not sure are widely supported. I know etc2
supports alpha in a single file with data, but still didn't work with that,
could you try do achieve this?

Sent from my Nexus 4
Il 17/nov/2014 13:38 "Eric" notifications@github.com ha scritto:

@ndorigatti https://github.com/ndorigatti yeah, well, on my tests it
works, my min sdk is 19 with GLES 3 so i would really love to see this
ported to ETC2 also since most of my users have it, i saw that there is a
bug request for this on the Android bugtracker hope it will be solved soon.

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[frmz]

@ndorigatti nope i have no competencies for that, i was hoping on a port from @nicastel :)

[nicastel]

Hello all, ETC2 is an extension of ETC1 wich means that an ETC1 texture is a vaild ETC2 texture. ETC2 add specific block mode to handle the case where ETC1 compression is not working well (bad quality).

Supporting ETC2 with good texture quality and performance can be tricky because you have to guess if you need to use a special ETC2 block mode or the default one (wich means the ETC1 mode).

Supporting only the alpha capabilities of ETC2 is a lot easier, I can implements this functionnality in the first time (same quality as ETC1 but with alpha support) if it suits your need but remember that it will only works if you have a device with Android 4.3 min and a GLES 3 compatible GPU.

[frmz]

@nicastel that would be great!! i think what would be even more awesome would be turning this project into a library that can be used instead of the ETC1Util provided by android with direct helper methods to convert an ARGB8888 or 565 bitmap into an ETC2/1 texture or a JPG/PNG file into a PKM one.

there is nothing around to do this runtime within an app and i think it would really help people a LOT.

[frmz]

BTW any way to convert an ARGB8888 image instead of using a 565?

[nicastel]

I am pleased to know that my library is useful to someone.

I have one more question. Which mode does best suit your need ? :

1. 4 bit/pixel : alpha handled as punch-trough (transparent or not transparent)
2. 8 bit/pixel : true alpha channel (256 transparency level)

This 2 modes needs two different implementation, mode 2 is more complicated to implement

[frmz]

@nicastel awesome! i think the most useful is the 2 since whe Bitmap.hasAlpha() returns true you dont know if the pixel is fully transparent or not

[ndorigatti]

i have the code for converting from PNG to PKM+alpha pkm and the PNG is
full alpha (not 565).
Is it useful?

2014-11-17 17:23 GMT+01:00 Eric notifications@github.com:

@nicastel https://github.com/nicastel awesome! i think the most useful
is the 2 since whe Bitmap.hasAlpha() returns true you dont know if the
pixel is fully transparent or not

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[frmz]

@ndorigatti that would be great! how do you load it then?