Abstract: A method and apparatus for generating a mask identifying a number of subpixels that are covered by a primitive includes the process of apportioning an image, comprising a plurality of scan lines into a plurality of sub-scan lines, such that a number of sub-scan lines crosses each pixel. A sample point is placed on at least one of the sub-scan lines. To determine the number of samples that are covered by a primitive, edge stepping is used to step along each edge of the primitive, generating a sub-scan line coordinate for the edge. The edge stepping hardware is used for stepping either on a sub-scan line granularity, for operation in anti-aliased mode, or on a scan line granularity, for operation in aliased mode. In anti-aliased mode, as each edge sub-scan line coordinate is generated, it is compared against the coordinates of a sample point on that sub-scan line, to determine whether or not that sample point is covered by the primitive.

Abstract: An antialiasing system is implemented in a graphics system of a computer. A memory control is associated with graphics system for controlling a frame buffer. The antialiasing system is situated in the memory control and is configured to receive from steppers (edge and span) new color values and new depth dimensions z at a plurality of subpixel locations. In turn, the antialiasing system analyzes color data pertaining to each pixel in the frame buffer, and if necessary, updates the color data. The color data is unique and minimizes memory requirements and accesses. Specifically, the color data includes a current display value that corresponds to the pixel, a reference color value that corresponds to one subpixel location, a reference depth dimension that corresponds with the one subpixel location, and reconstruction indicia that correspond with other subpixel locations and that can be utilized to derive respective depth dimensions and colors for the other subpixel locations.

Abstract: A color graphics pipeline has a separate encoder with a dither table for processing each color value in pixel data received from a host processor or rasterizer. The encoders modify color values and dither noise values and also combine both positive and negative dither noise values with the color values, for independent optimization of each color and for better edge detection in a color recovery filter within a decoder of the pipeline. Each encoder comprises the following elements. A comparator mechanism compares a color value with a predetermined cutoff value. A dither table provides dither noise values. An offset mechanism modifies the dither noise values to derive a modified dither noise value when the color value is greater than or equal to the predetermined cutoff value. An aliasing mechanism aliases the color value with other color values below the predetermined cutoff value to derive an aliased color value when the color value is less than the predetermined cutoff value.

Abstract: A color graphics pipeline has a separate encoder with a dither table for processing each color value in pixel data received from a host processor or rasterizer. The encoders modify color values and dither noise values and also combine both positive and negative dither noise values with the color values, for independent optimization of each color and for better edge detection in a color recovery filter within a decoder of the pipeline. Each encoder comprises the following elements. A comparator mechanism compares a color value with a predetermined cutoff value. A dither table provides dither noise values. An offset mechanism modifies the dither noise values to derive a modified dither noise value when the color value is greater than or equal to the predetermined cutoff value. An aliasing mechanism aliases the color value with other color values below the predetermined cutoff value to derive an aliased color value when the color value is less than the predetermined cutoff value.

Abstract: Color information lost in a computer graphics system as a result of encoding by dithering is recovered by passing the encoded data through a filter that has the same effective shape and size as the dither matrix used to encode the data. In a system that employs a dither matrix having 2.sup.N cells, up to N bits of color information, per color component, is recoverable.

Abstract: First next and second next pixel locations are selected simultaneously from among adjacent pixel locations and represent a straight line segment defined by two end locations and having a slope of one or less. An initialization process uses the .DELTA.X and .DELTA.Y of the desired line segment to find various constants, including an initial error term, an error term increment, an error term decrement, an error term double increment, an error term double decrement, and an error term increment-then-decrement. These represent, respectively, an increment in the X location without an increment to the Y location (a step S), an increment in the X location and an increment in the Y location (a jump J), a step followed by a step (two steps SS), two jumps (JJ), and either of a step-then-jump or a jump-then-step (SJ/JS). These five operations correspond to the only possible locations that might be selected, given any starting location.

Abstract: A color/texture interpolator (CTI) for use in rendering antialiased vectors in a computer graphics system comprises: an x-stepper circuit for receiving input data defining a vector to be rendered and generating respective pixel addresses of pixels composing the vector; a filter memory for storing predetermined filter values addressed according to the vector's minor axis subpixel addresses and slope; and a color interpolator for generating a color value for each pixel composing the vector.

Abstract: A technique of processing pipeline commands in parallel so as to minimize pipeline stalls. This is accomplished in accordance with the invention without need for the complex resource allocation techniques of the prior art by arbitrating access to critical pipeline resources on the phase of the system clock. For example, one control process may access the critical pipeline resource only during an even phase of the system clock, while a second control process may access the critical pipeline resource only during the odd phase of the clock. These processes may run at the same time if the pipelined instructions being executed by each process have no data dependencies since structural hazards are effectively eliminated by time-sharing the data buses on the respective phases of the system clock. The benefits of dynamically scheduled pipelined systems may thus be obtained without the complex scoreboarding and other scheduling algorithms used in the prior art to prevent pipeline hazards.

Abstract: A scan conversion algorithm for rendering antialiased vectors in a multi-processor graphics system comprises the following steps: providing signals to the processors indicative of scan lines the respective processors are responsible for, determining a first set of storage pixels to be rendered by the processors, rendering such storage pixel of the first set simultaneously, each by a different processor, determining a second set of storage pixels to be rendered, and rendering each of the second set of storage pixels substantially simultaneously by a different one of the processors. The determinations of the first and second sets of storage pixels are made in accordance with the signals indicative of scan lines for which the respective processors are responsible.

Abstract: A three-dimensional frame-buffer memory organized into a series of planes each storing one bit representative of a pixel on the display can draw a figure onto one of the planes. The figure can then be copied to preselected ones of the other planes while the first plane is cleared. A bit block transfer can be performed from an "invisible" portion of the first plane to pre-selected ones of the other planes.

Abstract: A system for clipping polygons representing three-dimensional objects to produce a representation of the portion of the objects in a desired viewing space is disclosed. A guardband space at least partially enclosing the viewing space is defined. The polygons are compared to the guardband space to determine which polygons intersect at least one of the guardband planes defining the guardband space. The intersecting polygons are also compared to the viewing space to determine if they intersect at least one of the viewing planes defining the viewing space. Only polygons intersecting both a viewing plane and a guardband plane are clipped.

Abstract: An image within a window on a scanned display device driven by a video generator is replaced with a preselected background color within one frame. The contents of the memory used to refresh the display can thus be changed in a background mode so that the user is unaware of the operation which he or she perceives as "instantaneous". Circuitry determines whether the scan is within the boundaries of the window and, if it is, generates a forcing signal which directs a look-up table within the video generator to a predetermined address which corresponds to a preselected background color. The invention can utilize existing circuitry in the video generator for generating synchronizing and blanking signals.