Data structures, methods and primitive block generators for storing primitives in a graphics processing system. The method includes: receiving a primitive associated with state data that defines how the primitive is to be rendered; determining whether the state data associated with the received primitive matches state data for a current primitive block; and in response to determining that the state data for the received primitive matches the state data for the current primitive block: determining, based on one or more primitive section size constraints, whether the received primitive is to be added to a current primitive section of the current primitive block in a data store; in response to determining that the received primitive is to be added to the current primitive section, adding the received primitive to the current primitive section; and in response to determining that the received primitive is not to be added to the current primitive section: outputting the current primitive section; reconfiguring the data store to store a new primitive section for the current primitive block; and adding the received primitive to the new primitive section for the current primitive block.