Patent ID: 7106275

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, wherein each layer pixel has an opacity value and wherein at least one of the overlapping layers has a fade value that specifies an overall opacity of the at least one of the overlapping layers, 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 a) 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: a.1) initializing an accumulator color value and an accumulator opacity value; a.2) selecting one of the layers in the set of at least two layers, the selected layer having a layer pixel corresponding to the image pixel, the layer pixel having a color value; a.3) compositing the color value of the layer pixel with the accumulator color value, and compositing at least one of the opacity value of the layer pixel and the fade value of the selected layer with the accumulator opacity value; a.4) storing the accumulator color value and the accumulator opacity value resulting from a.3); a.5) determining whether layer pixels for any remaining layers in the set of at least two layers should be processed; a.6) responsive to a.5) indicating that layer pixels for any remaining layers should be processed, repeating a.2) to a.6); and a.7) outputting the accumulator color value; wherein, for each defined tile, the set of layers that overlap within the tile is homogenous throughout the entirety of the tile.