Patent ID: 7330192

Claim:
A computer-implemented method for combining at least two overlapping layers to render an image, the image containing a plurality of image pixels, each overlapping layer containing a plurality of layer pixels, each layer pixel corresponding to one of the image pixels, the method comprising: a) defining a tile, the tile comprising a subset of the image pixels delimited according to an area of overlap among a set of at least two layers, so that a first portion of the image lies within the tile and a second portion of the image lies outside the tile; and b) processing the first portion of the image distinctly from the second portion of the image by, for at least one image pixel in the defined tile: b.1) initializing an accumulator color value; b.2) selecting at least one layer in the set of at least two layers, each selected layer having a layer pixel corresponding to the image pixel, the layer pixel having a color value; b.3) for each selected layer, compositing the color value of the layer pixel with the accumulator color value and storing the resulting accumulator color value in a computer readable memory; and b.4) outputting the accumulator color value; wherein, for each defined tile, the set of layers that overlap within the tile is constant throughout the entirety of the tile.