Cooperative filter and raster operation evaluation model

Abstract

A method and apparatus for handling transparency operatives simultaneously with raster operatives in a graphics environment. This is achieved by introducing filter operations to obtain the effect of transparency. Filter operations work cooperatively with grayscale and continuous-tone color raster operations. The introduction of filter operations, and their cooperation with raster operations allows this otherwise computationally complex problem to be served by a single hardware circuit for use in real-time applications such as monochrome and color laser printing. The solution is also applicable to displaying complex graphics on a video display device. A suitable apparatus receives graphics language commands which define the image to be displayed and generates a set of graphics orders from the graphics language commands representing the image to be displayed. The apparatus includes an image generator for generating a bitmap image from the graphics orders. A raster operation model is used for processing multiple-bit pixels in a source, in a pattern and in a destination, and a filter operation model is used for processing multiple-bit pixels in the source, pattern and destination. The raster operation model and the filter operation model operate cooperatively to modify the destination.