Support for compressed texture formats

[krapnikkk]

• TextureOptions added compressed property
• supportedExtensions added EXT_texture_compression_bptc and EXT_texture_compression_rgtc
• s_textureInternalFormatInfo added compressed texture formats

[greggman]

Thank you for the PR.

Are you actually using this?

• createTexture(gl, { src, width, height, internalFormat })

  This version would work. Do we care about other versions?

  For example, the non-compressed version will try to guess
  the width and/or height. Maybe that's not useful for compressed
  textures though. If we did want to do it, the code doing
  the guessing needs to take block sizes into account.

  If not, should we error if it's compressed and you don't
  pass in width and height?

• options.compressed

  Is this needed? It seems like you could have an internal function,
  isCompressedInternalFormat that you can call to decide
  whether or not to call compressedTexImage2D.

• can you add some tests?

  At least WebGL2 requires a few compressed formats to work
  so would be good to pick 1 or 2 and add a test that it works.

[krapnikkk]

Thanks for your reminder. The previous code application is often narrow.

• Added a prompt for direct error if width and height are not set.

• Added the compressed attribute to simplify the code, because before calling createTexture, getting internalFormat and srcData requires a lot of code. If an internal function isCompressedInternalFormat is added, it can only manage an array internally, and then judge according to the internalFormat passed in. It is better to leave this configuration to the user.

• Added test compressed texture format

[greggman]

I merged it. Thanks again for the PR.

I made several changes. See 8f53aa8 and 0128db9

Note: I got rid of the compressed option like I suggested. Internally there's a isCompressedInternalFormat type function. It did not require a large table. Also, I'm not sure what you were trying to do with looping on levels is not how twgl is designed so I removed that code.

Normally in twgl you upload level 0 and it auto geneartes mipmaps if possible. Of course it can't do this for compressed textures. For both compressed and uncompressed textures, you can only set mip level > 0 using setTextureFromElement or setTextureFromArray. You can't do with createTexture.