A method of rasterising a line in a graphics processing pipeline, the line having a start point and an end point and the method comprising, for each pixel in an input set of pixels: determining whether the end point of the line is in a diamond test area within the pixel, wherein the diamond test area is defined by a top point, a left point, a bottom point and a right point connected by edges to form a diamond; in response to determining that the end point is not in the test area, determining whether the start point of the line is in the diamond test area within the pixel; in response to determining that the end point is not in the diamond test area and the start point of the line is in the diamond test area, adding the pixel to a set of pixels to be drawn as part of the line; in response to determining that neither the start point nor the end point of the line are in the diamond test area, determining if the line crosses more than one extended diamond edge, wherein an extended diamond edge is coincident with an edge of the diamond test area and extends beyond the diamond points that the edge connects; and in response to determining that the line crosses more than one extended diamond edge: determining if an extended line passing through the start and end point has a slope less than -1 or greater than +1 and touches the right point of the diamond test area; determining if the extended line touches the bottom point of the diamond test area; determining if the extended line is on a same side of each point of the diamond test area; and in response to determining that the extended line has a slope less than -1 or greater than +1 and touches the right point of the diamond test area or that the extended line touches the bottom point of the diamond test area or that the extended line is not on a same side of each point of the diamond test area, adding the pixel to a set of pixels to be drawn as part of the line. determining whether the end point of the line is in a diamond test area within the pixel, wherein the diamond test area is defined by a top point, a left point, a bottom point and a right point connected by edges to form a diamond; in response to determining that the end point is not in the test area, determining whether the start point of the line is in the diamond test area within the pixel; in response to determining that the end point is not in the diamond test area and the start point of the line is in the diamond test area, adding the pixel to a set of pixels to be drawn as part of the line; in response to determining that neither the start point nor the end point of the line are in the diamond test area, determining if the line crosses more than one extended diamond edge, wherein an extended diamond edge is coincident with an edge of the diamond test area and extends beyond the diamond points that the edge connects; and in response to determining that the line crosses more than one extended diamond edge: determining if an extended line passing through the start and end point has a slope less than -1 or greater than +1 and touches the right point of the diamond test area; determining if the extended line touches the bottom point of the diamond test area; determining if the extended line is on a same side of each point of the diamond test area; and in response to determining that the extended line has a slope less than -1 or greater than +1 and touches the right point of the diamond test area or that the extended line touches the bottom point of the diamond test area or that the extended line is not on a same side of each point of the diamond test area, adding the pixel to a set of pixels to be drawn as part of the line. determining if an extended line passing through the start and end point has a slope less than -1 or greater than +1 and touches the right point of the diamond test area; determining if the extended line touches the bottom point of the diamond test area; determining if the extended line is on a same side of each point of the diamond test area; and in response to determining that the extended line has a slope less than -1 or greater than +1 and touches the right point of the diamond test area or that the extended line touches the bottom point of the diamond test area or that the extended line is not on a same side of each point of the diamond test area, adding the pixel to a set of pixels to be drawn as part of the line.