Abstract: There is provided a computer-implemented method of defining bounding boxes for a primitive in a tile-based graphics processing pipeline comprising determining a part-way point on the primitive, wherein, for each pair of vertices, a part-way point is part-way between that pair of vertices, and defining a plurality of bounding boxes, wherein each bounding box intersects a part-way point. Also provided is a bounding box generation circuit comprising a part-way point calculation circuit to determine a part-way point on the primitive, wherein, for each pair of vertices, a part-way point is part-way between that pair of vertices, wherein the bounding box generation circuit to define a plurality of bounding boxes based upon the determined part-way point, wherein each bounding box intersects a part-way point. A method of defining bounding boxes for a point primitive is also provided.