Stage3D compressed textures – Introducing the ATF SDK

We introduced Stage3D last year and the momentum behind has never stopped growing but there is one area we did not give all the details. The ATF file format, it is mentioned here and there, so what's up with this? Some of you may have seen it in the documentation for Stage3D referred as the compressed texture file format, but we never shared any tools to create those famous ATF textures.
Before we package the ATF tools with the AIR SDK, I am happy to share here in advance the ATF tools so that you guys can start leveraging the ATF format now!
So what is it?
First, let's start by talking about what compressed textures are.
When doing GPU programming with any technology, you have two options for how you handle your textures. You can go compressed or uncompressed, very simple. So, what is the difference?

1. When using uncompressed textures, a good old uncompressed file format like PNG is used and uploaded to the GPU.
2. Because GPUs don't support such a file format natively, your texture is actually stored in CPU memory, when it could actually be stored on the GPU memory!
3. Same thing applies for JPEG images, make no mistake, graphics chipsets don't know anything about JPEG which would also be decoded on CPU memory.
4. Of course, each platform has different support for compressed textures depending on the hardware chipset being used.

Now get ready for the fun! Here is below a little table to illustrate it:

Platform	Format
ImgTech (iOS)	PVRTC
Qualcom (Android)	ETC1
Mali (Android)	ETC1
NVidia (Android)	ETC1/DXT1/DXT5
Android (PowerVR)	PVRTC/ETC1
Windows	DXT1/DXT5
MacOS	DXT1/DXT5

Why ATF?
As you can imagine, if you would develop a game targeting iOS, Android and desktop, you would need to supply your textures compressed to each format for each platform. Which would look like this:

1. leaf.png encoded to DXT for Windows and MacOS
2. leaf.png encoded to ETC1 or DXT for Android (Nvidia)
3. leaf.png encoded to PVRTC for iOS (ImgTech)

Of course it is a pain to provide all the different versions of the textures, detect at runtime which platform you are running on and upload the corresponding texture. Wouldn't it be cool if you could just rely on one single container, that would wrap all the textures for each platform and Flash Player or AIR would extract automatically the texture required depending on the platform? So here comes ATF.
The ATF internals
Really, think about the ATF format as a container for lossy images. Here is below a little figure showing very sinply the structure of a default compressed ATF file:
Read more: Stage3D compressed textures – Introducing the ATF SDK