mipgen can now emit basis-encoded KTX2 files. Both the desktop and
web "suzanne" samples use this as a test for compressed textures.
This PR does not add KTX2 support to glTF, but it's on the way.
`BasisEncoder` has a builder style API that calls the basis encoder to
create KTX2 files. This hides some low-level BasisU features that we are
not using, like file I/O and mipmap generation.
`Ktx2Reader` is an easy-to-use API for creating Filament textures from
KTX2 files. Its API primarily consists of these two methods:
bool requestFormat(Texture::InternalFormat format);
Filament::Texture* load(const uint8_t* data, size_t size);
The first method is used to build an ordered list of formats that are
supported by your hardware. The second method consumes the contents of a
basis-encoded KTX2 file and attempts to produce a Filament texture with
a preferred format.
IMPORTANT: Our tools still let you use KTX1 for non-compressed images
because it is useful for HDR, but you can no longer use KTX1 for
block-compressed data.
Partial fix for #4771.
While this solves the builder leak, it does not solve the tiny leak
incurred every time you call `getInstance` on a component manager
without calling embind's `delete` method afterwards. Since there's no
way to auto-delete component instances, this CL fixes up our sample
code and docstrings.
Fixes#429
Note that we need to allow clients to find out if compressed textures
are supported BEFORE the engine is created, so that they can start
downloading the correct set of texture files. To allow this, we now
expose a getSupportedFormats function that creates a throw-away canvas
in order to query extensions (creating a temporary canvas is a technique
that we also used in the old PNG decoder that we removed in 7b36ed4)
