A method and apparatus is disclosed for independently displaying one of a plurality of images on a display and for superimposing the plurality of images onto one another to produce a composite image. One or more bit planes are selected to constitute a group (defined to be a "surface"), and one or more additional bit planes are selected to constitute another group. The number of groups corresponds to the number of images to be independently displayed. The priority of one group over the other is selected. This ensures that the image from the one group (surface) appears to be "in front of" the images from the other group (surface) on the display. In the case of a color terminal, the colors associated with each group are selected. A color map memory contains a plurality of brightness indices which determines image brightness. Associated with each index is one or more color indices. The bits associated with each pixel are used as an index to the color map memory by locating the corresponding color (or gray) indices. The associated brightness index is noted, and converted to an analog voltage for determination of image brightness. In response to the selection of the groups mentioned hereinabove, and the designation of priority among groups, the firmware recomputes the color map in the color map memory, that is, the color indices are set based upon the number of selected groups and the number of bit planes per group, and selected ones of the brightness indices are recomputed based on the designated priority among groups. Due to the ability of the present invention to select one or more bit planes to constitute a group, and due to the firmware's ability to recompute the color map, one or more images can be displayed on the CRT, either independently of one another, or superimposed upon one another to produce a composite image.
An image output device includes a tone pattern generator 33 of an image processing portion 3 which, on the basis of image data representing border positions of a plurality of regions of an image divided according to density values thereof, generates a tone dot pattern corresponding to the density value of the region, a closed region assigning circuit 32 for assigning a closed region on an image memory corresponding to the resolution d of the respective closed region of the image, and a filling out processing circuit 34 writes the tone dot pattern in the assigned closed region as image data having the resolution d.
Segment data expressing segments which form the contour of a graphic figure are provided. Connection mode data expressing the connection modes between the segments are generated. The loops included in the graphic figure are detected on the basis of the segment data and the connection mode data. Even if the segments imperfectly define the contour, the loops can be detected through the step of correcting the segment data and the connection mode data.
A graphics display apparatus includes a raster-scanned CRT refreshed from a bit-for-pel refresh buffer loaded with bit patterns by a microprocessor corresponding to a desired image. To display shaded areas, additional control logic draws an outline of the area in an auxiliary memory, preferably using Bresenham's Algorithm, according to specified rules. Edge filling logic consisting of EXCLUSIVE-OR gates is used to draw the filled area in the refresh buffer as the outline is read from the auxiliary memory into the refresh buffer. This hardware assistance by the control logic and edge fill logic to the microprocessor enables complex areas to be drawn and filled without unduly degrading the performance of the microprocessor.
A method and apparatus for writing a vector of data into a random access memory at high speed wherein the random access memory (RAM) is partitioned into blocks of addressable storage sites and wherein storage sites within each block are individually accessible. A vector generator provides addressing and storage site enabling signals to the RAM. Boundary detectors monitor the addressing and storage site selection signals to determine whenever storage sites within a new block of storage sites are sought to be addressed. When a boundary transition is detected, a control signal is provided to the vector generator which slows the operation of the vector generator for a period of time sufficient to permit the RAM to accept a new address. For all other addresses, the vector generator is permitted to operate at a higher speed wherein access to the RAM is made by way of enabling specific storage sites within the block of storage sites being written into. The invention further providing a method and apparatus for generating surface-fill vectors, wherein a vector generator which implements the Bresenhem Algorithm is employed to generate instructions for locating points corresponding to line segments that bound the surface to be filled. The instructions are evaluated such that the X address for a given point is recorded whenever an instruction is issued which indicates a Y address change. The recorded X address are correlated to the Y coordinates over which the surface extends. The correlated X and Y addresses then define end points of surface fill vectors which can fill in the surface.
A system (30) draws antialiased polygons. A CPU (32) is connected to a floating point processor (FPU) (34) by bus (36). The CPU (32) is connected by a 32-bit system bus (38) to a random access memory (RAM) (40), a cache (42) and an interface (44) in graphics subsystem (45). The interface (44) is connected by bus (46) to graphics processor (48). The graphics processor (48) is connected by 120-bit graphics bus (50) to frame buffer (52). The frame buffer (52) is connected to a video digital to analog converter (DAC) (54) by bus (56). The DAC (54) is connected to video display (58) by line (60). The graphics processor (48) use a technique known as super-sampling to combat the effects of aliasing. In aliased mode, the graphics processor (48) use 16 array sites to sample 16 pixels (72). When drawing a polygon or line in antialiased mode, the graphics processor (48) uses the 16 sites to sample at 16 locations (120) within a single pixel (72). The antialiasing is done by determining what proportion of the locations (120) within each pixel (72) are within the polygon and setting a color of each pixel (72) on the basis of the proportion.
