What internal format combinations would work for this following code example, if my intention is to have raw storage allocated as a non compressed texture and the texture view interpreting this as BC5 / RGTC ?
GLuint texId;
glGenTextures(1, &texId);
glBindTexture(GL_TEXTURE_3D, texId);
glTexStorage3D(GL_TEXTURE_3D, 1, GL_RGBA32UI, 4, 4, 16);
glBindTexture(GL_TEXTURE_3D, 0);
assertNoError();
GLuint viewId;
glGenTextures(1, &viewId);
glTextureView(viewId, GL_TEXTURE_3D, texId, GL_COMPRESSED_RG_RGTC2, 0, 1, 0, 1);
assertNoError();
glDeleteTextures(1, &viewId);
glDeleteTextures(1, &texId);
assertNoError();
This example failed with INVALID_OPERATION and the GL debug output message says:
Internal formats neither compatible nor identical.
To narrow my question by exclusion:
You cannot allocate storage of a non-compressed format and view it with a compressed format. Or vice-versa. You can copy between compressed and uncompressed formats via glCopyImageSubData. But you can't do the kind of "casting" that you're trying to do.
Furthermore:
TexStorage cannot have the compressed internal format. This is GL 4.5 and that has been removed.
You cannot use generic compressed image formats, but specific formats (like GL_COMPRESSED_RG_RGTC2) are still available. Just not for 3D textures (BPTC can work with 3D textures, but not RGTC).
Vulkan has a mechanism for creating a VkImage of a compressed format from which you can then create a VkImageView with an appropriate uncompressed format (the reverse isn't allowed, but that doesn't really matter all that much). To do this, the image has to be created with the VK_IMAGE_CREATE_BLOCK_TEXEL_VIEW_COMPATIBLE_BIT creation flag, and the view must use a 32-bit unsigned int format, with sufficient components for each pixel of the view to correspond to the block byte size for the format.