A high speed arrangement for generating smooth lines of consistent thickness regardless of slope in a raster type display system such as a computer graphics system. A digital differential analyzer is employed for determining Y-position information to n bits of fraction for each integral step in X within a single operative clock cycle. All pixel positions are identified that are relevantly proximate to the starting end point of the line, to the concluding end point, and each one-dimensional array of at least three contiguous pixel positions encompassing a cross-section of the interior portion of the line. Intensity values are determined for each such identified position pixel based upon its distance from the true line, with the intensities of the pixel positions identified in each array being additionally determined based upon the slope of the line. For crossing-line situations in color systems, proportional weighting apparatus is provided which generates a new pixel-position value based upon the existing intensity value, the desired color of the line and the intensity value associated to the crossing line, with the latter constituting a proportionality constant.