A computer implemented method of fracturing a shell of a three-dimensional object, to define layer data for an additive manufacturing process of the object the method comprising: receiving a shell of a three-dimensional object composed of a plurality of facets including first facets and distinct second facets; and forming layer data defining a plurality of layers of the shell at least some of the plurality of layers including respective first fragments produced by first facets and exclusive of second facets, and at least some of the plurality of layers including second fragments produced by second facets and exclusive of first facets, wherein at least one layer of the plurality of layers includes both a first fragment of the respective first fragments, and a second fragment of the respective second fragments, and wherein for a layer of the at least one layer that includes both a first fragment of the respective first fragments, and a second fragment of the respective second fragments, forming the layer data that defines the layer includes: receiving the layer which defines an initial polygon composed of first and second segments produced by respective ones of first and second facets that intersect the layer, a second segment of the first and second segments meeting other segments at a pair of vertices; copying the pair of vertices a depth within the initial polygon to a corresponding pair of vertices; creating segments to connect vertices of the corresponding pair of vertices, and connecting vertices of the pair of vertices with respective ones of the vertices of the corresponding pair of vertices to form an initial second polygon within the initial polygon; performing a Boolean intersection between the initial polygon and initial second polygon to produce a second polygon; performing a Boolean difference between the initial polygon and second polygon to produce a first polygon, wherein the first fragment of the layer defines the first polygon, and the second fragment of the layer defines the second polygon. receiving a shell of a three-dimensional object composed of a plurality of facets including first facets and distinct second facets; and forming layer data defining a plurality of layers of the shell at least some of the plurality of layers including respective first fragments produced by first facets and exclusive of second facets, and at least some of the plurality of layers including second fragments produced by second facets and exclusive of first facets, wherein at least one layer of the plurality of layers includes both a first fragment of the respective first fragments, and a second fragment of the respective second fragments, and wherein for a layer of the at least one layer that includes both a first fragment of the respective first fragments, and a second fragment of the respective second fragments, forming the layer data that defines the layer includes: receiving the layer which defines an initial polygon composed of first and second segments produced by respective ones of first and second facets that intersect the layer, a second segment of the first and second segments meeting other segments at a pair of vertices; copying the pair of vertices a depth within the initial polygon to a corresponding pair of vertices; creating segments to connect vertices of the corresponding pair of vertices, and connecting vertices of the pair of vertices with respective ones of the vertices of the corresponding pair of vertices to form an initial second polygon within the initial polygon; performing a Boolean intersection between the initial polygon and initial second polygon to produce a second polygon; performing a Boolean difference between the initial polygon and second polygon to produce a first polygon, wherein the first fragment of the layer defines the first polygon, and the second fragment of the layer defines the second polygon. receiving the layer which defines an initial polygon composed of first and second segments produced by respective ones of first and second facets that intersect the layer, a second segment of the first and second segments meeting other segments at a pair of vertices; copying the pair of vertices a depth within the initial polygon to a corresponding pair of vertices; creating segments to connect vertices of the corresponding pair of vertices, and connecting vertices of the pair of vertices with respective ones of the vertices of the corresponding pair of vertices to form an initial second polygon within the initial polygon; performing a Boolean intersection between the initial polygon and initial second polygon to produce a second polygon; performing a Boolean difference between the initial polygon and second polygon to produce a first polygon, wherein the first fragment of the layer defines the first polygon, and the second fragment of the layer defines the second polygon.