Combining raster and vector data in the presence of transparency

A computer program product, tangibly stored on a machine-readable medium, for preparing one or more vector data objects for rendering, comprising instructions operable to cause a programmable processor to:

• receive a first object that is a vector data object;
• define clipping states for the first object, each clipping state representing, for a stage of rendering, an image associated with the first object, wherein the clipping states have an order in which they are to be rendered;
• for each clipping state, determine whether a clipping path is needed to render the image represented by the clipping state, and when a clipping path is needed, generate clipping instructions for calculating a clipping path for the clipping state, and when a clipping path is not needed, generate clipping instructions indicating that a clipping path is not needed;
• for each clipping state, generate rendering instructions for rendering the image represented by the clipping state;
• associate the generated clipping and rendering instructions to the corresponding clipping states;
• for each clipping state, calculate a may-cover region that a rendering device may mark, the calculation being based on the associated clipping instructions and the precision of the rendering device;
• for each clipping state, calculate a must-cover region that the rendering device must mark, the calculation being based on the associated clipping instructions and the precision of the rendering device;
• and
• calculate a final may-cover region for each clipping state, including subtracting from the may-cover region of a clipping state the must-cover regions of all clipping states that are to be rendered after the current clipping state is rendered.