A primitive block assembly module for assembling primitive data into primitive blocks in a graphics processing system, the primitive block assembly module comprising: an input configured to receive primitive data for one or more primitives of a scene for rendering a plurality of views of the scene, wherein the primitive data comprises a plurality of parameters and the plurality of views comprises at least a first view and a second view; and processing logic arranged to receive and store control data identifying which vertex parameters are in a first plurality of vertex parameters and which vertex parameters are in a second plurality of vertex parameters, generate a primitive block (200, 400, 500) using the control data and store primitive data for the one or more primitives and vertex data for a plurality of vertices in the primitive block (200, 400, 500), wherein: the primitive data for a primitive comprises a reference to one or more of the plurality of vertices; wherein the vertex data comprises, for each vertex in the plurality of vertices: for each of the first plurality of vertex parameters, a vertex parameter value for the first view and a vertex parameter value for the second view; and for each of the second plurality of vertex parameters, a single vertex parameter value for both the first and second views, characterized in that the control data is determined in an offline process by: inspecting, for each vertex parameter, code that generates the parameter values; in response to determining that, for a vertex parameter, the code is capable of generating a vertex parameter value for the first view for at least one vertex that does not match the vertex parameter for the second view for the same vertex, assigning the vertex parameter to the first plurality of vertex parameters; and in response to determining that, for a vertex parameter, the code is not capable of generating a vertex parameter value for the first view for any vertex that does not match the vertex parameter for the second view for the same vertex, assigning the vertex parameter to the second plurality of vertex parameters. processing logic arranged to receive and store control data identifying which vertex parameters are in a first plurality of vertex parameters and which vertex parameters are in a second plurality of vertex parameters, generate a primitive block (200, 400, 500) using the control data and store primitive data for the one or more primitives and vertex data for a plurality of vertices in the primitive block (200, 400, 500), wherein: the primitive data for a primitive comprises a reference to one or more of the plurality of vertices; wherein the vertex data comprises, for each vertex in the plurality of vertices: for each of the first plurality of vertex parameters, a vertex parameter value for the first view and a vertex parameter value for the second view; and for each of the second plurality of vertex parameters, a single vertex parameter value for both the first and second views, for each of the first plurality of vertex parameters, a vertex parameter value for the first view and a vertex parameter value for the second view; and for each of the second plurality of vertex parameters, a single vertex parameter value for both the first and second views, characterized in that the control data is determined in an offline process by: inspecting, for each vertex parameter, code that generates the parameter values; in response to determining that, for a vertex parameter, the code is capable of generating a vertex parameter value for the first view for at least one vertex that does not match the vertex parameter for the second view for the same vertex, assigning the vertex parameter to the first plurality of vertex parameters; and in response to determining that, for a vertex parameter, the code is not capable of generating a vertex parameter value for the first view for any vertex that does not match the vertex parameter for the second view for the same vertex, assigning the vertex parameter to the second plurality of vertex parameters. inspecting, for each vertex parameter, code that generates the parameter values; in response to determining that, for a vertex parameter, the code is capable of generating a vertex parameter value for the first view for at least one vertex that does not match the vertex parameter for the second view for the same vertex, assigning the vertex parameter to the first plurality of vertex parameters; and in response to determining that, for a vertex parameter, the code is not capable of generating a vertex parameter value for the first view for any vertex that does not match the vertex parameter for the second view for the same vertex, assigning the vertex parameter to the second plurality of vertex parameters.