Evans & Sutherland Computer Corporation

Gary S Watkins

Russell A Brown

Michael A Cosman

Michael D Drews

Glen A Eckart

A geometric processor provides object primitives, as triangles, in graphic display image space to support a dynamic display. The image space is defined by pixels, in turn specified in arrays as spans. In a multi-level scanning operation, primitives are scanned at a first level to locate lapped spans that are lapped by primitives. At a second level, spans are scanned to process pixels that are lapped by primitives. An alternative embodiment discloses three-level scanning in association with parallel pixel processing. Concurrent texturing structure operates along with cache memories.

Computer graphics pixel rendering system with multi-level scanning

An adaptive pixel multisampler generates pixel data for display by using sub-pixel areas to more broadly define the space of a pixel. A sub-pixel area is defined as having a 'hole' within it that is occupied by a portion of each of the adjacent sub-pixel areas. This means that while the sub-pixel areas interlock, they do not overlap which would be wasteful of memory space. Accordingly, a pixel is newly defined as extending over a larger area than a standard contiguous pixel definition of the prior art allows. The larger pixel thus provides a wider sampler area which is then used as a means for generating a higher quality anti-aliased image on the display.

Computer graphics system with adaptive pixel multisampler

An adaptive pixel multisampler generates pixel data for display using an interlocking sub-pixel sampling pattern and a frame buffer organized as a per-polygon, per-pixel heap. The interlocking sampling pattern provides the advantages of a multi-pixel shaped filter without pixel-to-pixel cross communication and without additional sub-pixels. The per-polygon, per-pixel heap allocates frame buffer memory so that each pixel will have one set of data stored in the frame buffer for every polygon that influences that pixel. This memory allocation scheme can significantly reduce frame buffer memory requirements. The polygon data is blended to properly handle processing of transparent polygons and polygon edges without the degradation of image quality found in conventional computer graphics systems.

Objects contending for representation in pixels of a graphics display selectively are awarded a fractional area within a pixel on the basis of: coarse calculations in the Z dimension, aggregate demands of the objects and blending techniques free of binary position resolutions. Specifically, the area occupied by a polygon within a pixel is represented using a single number .alpha., which may variously be defined, for example, a value of '0' indicates no area occupied within the pixel, while a value of '255' indicates full pixel coverage. Fine calculations in the Z dimension for binary resolutions are avoided by the blending techniques with attendant antialiasing. A chain of mixer units for storage and blending in pipeline processing compensate the non-associative characteristic of repeated blending.

Attribute blending system for composing computer-graphic images from

Primitive data in the form of defined lines for a computer graphics display is processed as by interpolating triangles, as during scan conversion, and by treating lines as triangle edges. An offset point is selected, e.g. offset perpendicularly from the line midpoint a distance of one-half the line length to define a triangle vertex along with the line endpoints. The resulting triangle is interpolated for example as with barycentric coordinates. Accordingly, the line may be interpolated, e.g. shaded, as though it were an edge of the defined triangle. For lines, sample points are coerced to lie on the triangle edge.

System for line interpolation for computer graphics displays

Barycentric coordinates are determined using data readily available in computer graphics systems and defining polygons in world space so as to interpolate such polygons with regard to pixels selected by scan conversion. The barycentric coordinates are employed to interpolate the polygons, for example to accomplish smooth shading or texture mapping. The process of the system involves defining primitive data (e.g. polygons) in a space not subject to nonlinear distortion (e.g. world space), transforming select primitive data to a space that is subject to nonlinear distortion, calculating in the space subject to nonlinear distortion (e.g. screen space) a set of areas (e.g. pixels) within a defined primitive (e.g. polygon) using data transformed to space subject to nonlinear distortion, transforming the set of areas to the space not subject to nonlinear distortion, determining at least one differential value (rate of change) of a variable for the primitive, calculating display data that is not subject to nonlinear distortion and using the differential to provide display data. For example, at a pixel, the rate of change in coordinate value (differential) is determined and utilized in texture mapping to facilitate the selection of levels of fuzziness with regard to picture detail for the pixel. Specifically, the differentials are in the coordinates of the texture du land dv.

System for polygon interpolation using instantaneous values in a variable

For a raster-scanned, video display apparatus, individual pixel display data is stored in a double image frame buffer. A valid count buffer then holds a count for each pixel. Current valid counts are stored, as at times of image buffer updating which updating includes storing display data changes and a fraction of the total display (background). At times of display, current counts from the count buffer are tested against valid counts as stored for each pixel in the valid count buffer to determine the selection of display data from the image frame buffer or alternate background data. A window frame buffer resolves the display into windows that are accommodated by the system with valid counts for each window.

Computer graphics dynamic control system

For use in a computer graphics apparatus, a data management system drives a multiple-window dynamic display. The display is formed by areas, e.g. pixels, and windows are variously defined in a display by assigning window codes to groups of areas. Image data for each area provided from a picture system is selectively registered in an image frame buffer in accordance with the defined windows. Valid data binary signals, designating currently valid image data in the image frame buffer are registered in three valid data buffers. The image data for each area is provided for a display from the selectively registered signals in the image frame buffer under control of the window codes and the valid data binary signals. Techniques are thus available for rapidly swapping portions of the frame buffer and selectively clearing and loading the image frame buffer. Areas not specified by signals from the image frame buffer are treated as background and driven with an appropriate display.

Computer graphics windowing system for the display of multiple dynamic

Image data is composed from primitives (polygons) to attain data for displays with the removal of hidden surfaces and smooth-appearing edges. Defined polygons are tested for priority in a determined field of vision by scan conversion to specify individual picture elements (pixels). Polygon contention for pixels is resolved by determining the edge of intersection between the planes of such polygons and testing the signs of certain values in accordance with predetermined criteria. Subpixel priority is treated for similar resolution to provide improved antialiased images.

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Salt Lake City, UT, United States of America

Gary S Watkins