A method of moving blocks of pixel data, including window-identifying data, from a source area to a destination area within a frame buffer in a computer graphics system comprises the steps of: reading a block of pixel data from the source area into a pixel cache memory; combining source tiles with destination tiles in the cache; comparing pixel window identifiers read from the frame buffer with a pixel window identifier previously stored in the memory to determine whether the pixel window identifiers read from the frame buffer match the previously stored pixel window identifier; discarding each pixel whose corresponding window identifier does not match the previously stored window identifier; and updating the frame buffer with the pixel data not discarded.

A method for updating a single ported, pipelined Z-buffer where the Z-buffer is updated only after determining the beginning and ending location of a continuous group of pixel locations requiring updating in the Z-buffer.

A display system comprises a data base memory for storing data representing a picture, a display device for displaying the picture, and manipulation means for causing the display device to display a cursor at a position which is under user control. The picture is composed of objects and each object is represented in the data base memory by a segment which represents both the object and the position of the object in the picture. A pointer, which divides the address domain of the display device into at least two regions, is generated. The manipulation means provides a signal which identifies the region of the pictures in which the cursor is positioned, and this signal is compared with the contents of the data base memory to facilitate selection of an object which lies in the identified region of the picture.

Figure data processing apparatus and method in which data are sorted in a depth direction by executing hidden surface removing processing on all figure data to which a priority drawing number is not given, writing, in a display memory unit, portions or whole picture elements of figure data obtained after the hidden surface removing processing, again generating picture elements of each drawing figure, detecting entirely visible figures in which the picture element data written in the display memory unit are identical with the picture element data generated at the second time, and giving a drawing priority number to each of the entirely visible figures thus detected. The apparatus is adapted such that drawing figures are successively overwritten in the display memory unit based on the drawing priority numbers, as necessary.

A method for specifying a video window's boundary coordinates directly from a multi-color video signal to separate the signals high and low variance components. The method converts the analog multi-color video signal into respective color sequences of digital frames and transforms them into another sequence of digital frames that represent the intensity of the multi-color video signal. The method generates difference frames between successive transformed intensity frames and computes a row activity measure and a column activity measure from at least one of the difference frames. The video window's approximate boundary coordinates are determined from said row and column activity measures.