Loading ktx etc1 compressed textures

I have been trying to load compressed textures on OS X and in OpenGL ES 2 on RPi 3, with Texture2d::createFromKtx.

I compressed a png with crunch-osx like this:

crunch -file 01.png -fileformat ktx -etc1

The texture seems to be loaded, but nothing is shown, while uncompressed ktx, without the -etc1 option seems to be working, but since it is not compressed it has no use for me at the moment.

Could you suggest a way to load compressed textures in OpenGL ES 2?


It turns out that the OS X driver does not include etc1 texture support, but it works on the RPi, although it displays a warning:

|warning| static void cinder::gl::TextureBase::getInternalFormatInfo(GLint, GLenum *, GLenum *, bool *, bool *, bool *)[1b3] Unknown internalFormat:0x0

The gl::TextureData returned from parseKtx contains the proper 0x8D64, GL_ETC1_RGB8_OES internal format, so the warning might be harmless.