A method of rendering a graphical image described by an expression tree is disclosed. The expression tree has one or more parent nodes and one or more leaf nodes, each parent node representing a graphical operator and having branches to respective
descendent nodes. Each of the leaf node represents a graphic object. The method determines regions of one or more pixel locations in an output space of the image, with each region corresponding to a combination in the image of one or more the graphical objects. Next, for each said region, an activity state of corresponding parent nodes is determined using a predefined function for each corresponding operator. The method then generates, in parallel (1098), for each active one of the operators,
compositing instructions and pixel generation instructions. The
compositing instructions are stored in an operator
queue and pixel colors are generated using the pixel generation instructions, the pixel colors being buffered in an
operand queue (1300). Lastly, the generated pixel colors are composited (1400), for each pixel in the region, using the operators defined in the operator
queue, to output (800) a composited pixel value for each pixel in the region. Other
processing operations including operator reduction, flat color bypass, and
operand comparison are also discussed.