There is a small bug in the spince-c runtime documentation in the sample code which shows implementation of: "Implementing _spAtlasPage_createTexture is then as simple as:"

In the sample code the function name is

_AtlasPage_createTexture

but must be

_spAtlasPage_createTexture

Also the following:

// store the texture width and height on the spAtlasPage
// so spine-c can calculate texture coordinates for
// rendering.
self->width = texture->x;
self->height = texture->y;

must be:

// store the texture width and height on the spAtlasPage
// so spine-c can calculate texture coordinates for
// rendering.
self->width = texture->width;
self->height = texture->height;