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:// so spine-c can calculate texture coordinates for
// rendering.
self->width = texture->x;
self->height = texture->y;
// 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;
// so spine-c can calculate texture coordinates for
// rendering.
self->width = texture->width;
self->height = texture->height;