Gpu rendering of knockout groups

A system for rendering knockout groups, the system comprising:

• a storage;
• and
• a processor operatively coupled to the storage, the processor configured to execute instructions stored in the storage that when executed cause the processor to carry out a process including
• compositing, by a processor, each object of a knockout group with a backdrop of the knockout group, the knockout group including a plurality of objects encoded in a Portable Document Format (PDF) document, by
• blending a color of each pixel representing the respective object with a color of a pixel in the backdrop of the knockout group overlapped by the respective pixel independently of a shape of any of the objects of the knockout group, thereby producing an intermediate color of the respective pixel, and
• computing a final color of each pixel representing the respective object as a function of the intermediate color, the color of the pixel in the backdrop prior to the blending, and the shape of the respective object, thereby knocking out at least a portion of the pixel in the backdrop based on the shape of the respective object;
• and
• storing the final color of each pixel in a framebuffer for rendering on a display device.

A non-transitory computer readable medium having instructions encoded thereon that when executed by one or more computer processors cause the one or more computer processors to perform a process comprising:

• compositing, by a processor, each object of a knockout group with a backdrop of the knockout group, the knockout group including a plurality of objects encoded in a document, by
• blending a color of each pixel representing the respective object with a color of a pixel in the backdrop of the knockout group overlapped by the respective pixel independently of a shape of any of the objects of the knockout group, thereby producing an intermediate color of the respective pixel, and
• computing a final color of each pixel representing the respective object as a function of the intermediate color, the color of the pixel in the backdrop prior to the blending, and the shape of the respective object, thereby knocking out at least a portion of the pixel in the backdrop based on the shape of the respective object;
• and
• storing the final color of each pixel in a framebuffer for rendering on a display device.