Raster operation apparatus for executing a drawing arithmetic operation when windows are displayed

A raster operation apparatus comprising:

• memory means for storing data corresponding to processing units and comprising source data and destination data, said memory means comprising predetermined memory areas physically divided from each other, each predetermined memory area storing the data corresponding to a processing unit, said predetermined memory areas comprising:
• a first memory area storing the source data of one processing unit and,
• a second memory area storing the destination data of one processing unit;
• first register means for receiving and holding the source data of at least four units sequentially read out from said first memory area each of said processing units;
• second register means for receiving and holding the destination data of at least two units sequentially read out from said second memory area each of said processing unit and synthesized into said source data;
• shift means for receiving in parallel the source data held in said first register means and for producing received source data, for shifting the received source data to coincide with data start positions in a processing unit of said destination data and for producing shifted data, and for generating the shifted data in parallel every processing unit;
• at least two bit operating means for fetching the source data of a special processing unit generated from said shift means and the destination data of the second register means corresponding to said source data, for executing a predetermined bit arithmetic operation, and for producing new destination data;
• and
• control means for allowing said at least two bit operating means to alternately execute the predetermined bit arithmetic operation by fetching the source data from said shift means and the destination data from said second register means in parallel with supplying and holding of the source data into said first register means and supplying and holding of the destination data into said second register means.