Predictive object-sequence caching from prior page content

A system for rendering a page description language (PDL) document, the system comprising:

• a memory for storing data and a computer program;
• a processor coupled to the memory for executing said program, said program comprising instructions for:
• receiving a plurality of display lists, each display list comprising a plurality of display list objects;
• determining a repeated sequence of a predetermined number of consecutive display list objects across the display lists;
• determining a reusable sequence of display list objects, for the repeated sequence, by extending the repeated sequence to further consecutive display list objects, each occurrence of the reusable sequence being associated with a z-order position in a corresponding display list;
• subdividing at least one display list, at the z-order position of the reusable sequence in said display list, into a plurality of z-bands including a reusable z-band for the determined reusable sequence;
• generating a reusable intermediate graphical representation for the determined reusable sequence and a further intermediate graphical representation for at least one other z-band;
• merging said further intermediate graphical representation with the reusable intermediate graphical representation in accordance with an order of said z-bands;
• and
• rendering the page description language (PDL) document using the merged representations.

An apparatus for rendering a page description language (PDL) document, the apparatus comprising:

• means for receiving a plurality of display lists, each display list comprising a plurality of display list objects;
• means for determining a repeated sequence of a predetermined number of consecutive display list objects across the display lists;
• means for determining a reusable sequence of display list objects, for the repeated sequence, by extending the repeated sequence to further consecutive display list objects, each occurrence of the reusable sequence being associated with a z-order position in a corresponding display list;
• means for subdividing at least one display list, at the z-order position of the reusable sequence in said display list, into a plurality of z-bands including a reusable z-band for the determined reusable sequence;
• means for generating a reusable intermediate graphical representation for the determined reusable sequence and a further intermediate graphical representation for at least one other z-band;
• means for merging said further intermediate graphical representation with the reusable intermediate graphical representation in accordance with an order of said z-bands;
• and
• means for rendering the page description language (PDL) document using the merged representations.

A non-transitory computer readable medium having a computer program stored thereon for rendering a page description language (PDL) document, the program comprising:

• code for receiving a plurality of display lists, each display list comprising a plurality of display list objects;
• code for determining a repeated sequence of a predetermined number of consecutive display list objects across the display lists;
• code for determining a reusable sequence of display list objects, for the repeated sequence, by extending the repeated sequence to further consecutive display list objects, each occurrence of the reusable sequence being associated with a z-order position in a corresponding display list;
• code for subdividing at least one display list, at the z-order position of the reusable sequence in said display list, into a plurality of z-bands including a reusable z-band for the determined reusable sequence;
• code for generating a reusable intermediate graphical representation for the determined reusable sequence and a further intermediate graphical representation for at least one other z-band;
• code for merging said further intermediate graphical representation with the reusable intermediate graphical representation in accordance with an order of said z-bands;
• and
• code for rendering the page description language (PDL) document using the merged representations.

A method for rendering a page description language (PDL) document, the method comprising:

• receiving identifying metadata for a first occurrence of a sequence of reusable objects identified in a first display list, a reusable intermediate graphical representation for the sequence of reusable objects being cached for further reuse in a format intermediate between a display list and pixel data;
• identifying a second occurrence of the sequence of reusable objects in the PDL document using the received identifying metadata, the identified second occurrence being associated with a z-order position in the PDL document of the second occurrence;
• grouping objects of the PDL document into a plurality of z-bands, the plurality of z-bands including a reusable z-band for the identified second occurrence and a further z-band based on the z-order position of the second occurrence;
• generating a display list representation for the PDL document, by creating a reference to the cached reusable intermediate graphical representation for the reusable z-band at the z-order position of the identified second occurrence;
• and
• generating an intermediate graphical representation to render the PDL document, the intermediate graphical representation being generated by merging the reusable intermediate graphical representation with an intermediate representation for the further z-band using the generated display list representation.