International Business Machines Corporation

Bob C Liang

Bruce C Hempel

Jorge Gonzalez-Lopez

Gregory D Laib

David C Tannenbaum

Robert M Callahan

Timothy J Ebbers

Daniel G Gibbons

Nina Y Liang

Anthony M Fiore

David W Li

Michael J Phelps

Todd N Tsakiris

A graphics display system picking function tracks machine states of pickable primitive operators through the use of a pick stack and machine state memory. The pick stack operates as a stack when accessed by pipeline processors. Pipeline processors can add an element to the stack or remove elements from the stack as structures are processed. Selection or picking of an object causes a graphics control processor to randomly access the pick stack to determine the attributes of a picked primitive. The machine state memory is implemented as a video RAM allowing rapid copying of rows containing machine states for various structure levels in the hierarchy. A first area of the machine state memory stores the states relating to the structures in the hierarchy as they are executed. A second area retains an abbreviated state description for each pickable primitive while a final area contains abbreviated machine state information for picked objects to be echoed by the system. The pick stack and machine state memories operate together to provide rapid pick identification, picked primitive machine state identification, and picked primitive echoing. The use of separate picked primitive echo machine storage allows drawing of the picked primitives without a complete re-traversal of the displayed list. This also results in reduced processing time.

Picking function for a pipeline graphics system using hierarchical

A multi-processor graphics system including a general purpose system control processor for setting up the workstation environment and data traversal structures based upon an application model language description. Workload balancing and interprocessor communication is managed by defining a general purpose interface between the general purpose processor and special purpose graphics control processor. The system control processor accepts application program information in a standard form, such as a hierarchical graphics language definition, then converts it into generalized interface control blocks for communication to the graphics control processor. Graphics control processor is signalled by an interrupt from the system control processor to begin the traversal process. The graphics control processor can then access the standard control blocks contained in system memory and perform the traversal necessary to generate the requested graphics image. Generalized control blocks allow rapid adaptation to program changes and efficient communication between the general purpose and specialized processors.

Multi-processor graphics display system for displaying hierarchical data

A method for clipping two and three dimensional graphic primitives for use in a computer graphics workstation. During the first clipping stage, the system removes all graphic primitives which lie outside an arbitrary clipping volume or window that is an enlargement of the desired viewing volume or window. This clipping volume (window) is then projected and mapped onto a virtual viewport which is larger than the real viewport. After this mapping occurs, rendering effects (such as line styles, line width, pattern fill, hatch fill, etc.) are applied to the primitive. A subsequent stage of clipping is then applied to clip the virtual viewport to the real viewport which is the user's visible area. Use of the clipping volume (window) during the first stage of clipping makes it simpler to transform geometric primitives which are partially visible to the viewer, and gives visible primitives a richer set of invariant geometric properties so that their rendering effects may be more easily and correctly carried out.

Multistage clipping method

An interactive computer graphics display system processing method for identifying a displayed primitive that intersects an operator selected area of the display screen. Pursuant to the method, the operator selected area of the display screen is reverse mapped to world coordinate space; data representative of displayed geometric primitives is then clipped against the reverse mapped selected area in world coordinate space; and clipped data representative of displayed geometric primitives that intersect the reverse mapped selected area are identified for operator defined application processing. Further processing steps include mapping of the identified data to screen coordinate space and rasterization of the data for display in the screen monitor. A zoom processing method is also provided wherein an original operator defined zoom window is transformed from screen coordinate space to world coordinate space and the boundaries of the transformed window in world coordinate space are utilized as data clipping boundaries. After clipping, data representative of a displayed geometric primitive outside the inverse mapped zoom window is discarded, thus preventing the rerasterization of geometric primitives outside the zoom window. Further processing includes mapping of the identified data to a defined zoom window in screen coordinate space for operator viewing and selection of a particular geometric primitive for application processing.

Interactive computer graphics display system processing method for

A Pipeline and Parallel Processing system for generating Surface Patches for both Wireframe and Solid/Shaded Models in a Raster Graphics Display. The inputs to a Transformation Processor are the parameters for the Rational Bezier Surfaces: a 2-dimensional array of control points, and weights. The outputs are the coordinates of the corner points and the normals (to the surface) of the patches, which make up the surface. The system consists of three Pipeline stages: (1) A front-end processor fetches the data from memory and feeds the Transformation Processor; (2) four Floating Point Processors in Parallel for tessellating the surfaces into small patches; and (3) one Floating Point Processor for generating normals at the vertices of the small patches. The output is sent to the rest of the Graphics System for clipping, mapping, and shading.

Parallel surface processing system for graphics display

A method for traversal of primitives in a graphics display system includes calculating pick data for a predetermined primitive, testing the primitive for invisibility, exiting to a next graphics order if the invisibility step is positive, testing the primitive for detectability, exiting to a next graphics order if the detectability test is false when traversal is performed for pick correlation purposes, determining whether a transformation environment update is required, recalculating the transformation environment if required, binding display attributes for the primitive and processing subsequent graphics orders to draw the primitive. Also, to eliminate unnecessary storing of registers when an execute structure is processed, a number of registers are set aside for storing control flags to selectively store registers into the stack. If a flag pick is zero the contents of the corresponding register will be stored on the stack. If the contents of the flag are one, indicating that the contents of the corresponding register has been stored on the stack, the contents will not be stored again, thus saving time and execution of the traversal.

Traversal method for a graphics display system

A lighting model processing system for a computer graphics workstation's shading function includes multiple floating point processing stages arranged and operated in pipeline. Each stage is constructed from one or more identical floating point processors. The lighting model processing system supports one or more light sources illuminating an object to be displayed, with parallel or perspective projection. Dynamic partitioning can be used to balance the computational workload among various of the processors in order to avoid a bottleneck in the pipeline. The high throughput of the pipeline system makes possible the rapid calculation and display of high quality shaded images.

Pipelined lighting model processing system for a graphics workstation's

Polygon vertex data is processed in three steps to create a graphics display without hidden lines and without gaps in the displayed lines. The technique permits the processing of triangles rather than polygons having four or more sides. In the first step, the Z values for the display points for the visible edges of the polygons are identified and assigned a reserved value ZCLOSE in a frame buffer. In the second step, the polygons are tessellated into triangles and the Z values for the display points on the triangles are computed and each depth buffer storage location is updated so as to contain the value of points closest to the viewpoint while the frame buffer is written with a background color. In the final step, the Z values for the display points of the polygon edges are again computed and compared with the corresponding Z values in the depth buffer. The depth buffer is updated with the computed values if the stored value is equal to ZCLOSE or if the computed value represents a position closer to the viewpoint than the stored value and the frame buffer is then written with a foreground color for the display point in question.

Hidden line removal method with modified depth buffer

A display processor in a raster graphics display system includes a transformation, clipping and mapping feature which controls the transformation, clipping and mapping of graphics data. A control byte contains 5 bits identified as: M--Window to viewport mapping; P--perspective projection; D--2D/3D mode; T--transformation; and C--clipping. Each bit in the control byte is tested to determine what operations are to be performed on the figure to be drawn.

Data transformation and clipping in a graphics display system

A method for clipping fixed characters against one or more clipping boundaries for display in a graphics display system, includes the steps of: storing fixed characters to be displayed; defining a window in a first coordinate space against which said characters shall be clipped along one or more boundaries thereof; clipping an inverse character box for each fixed character to be displayed against said defined clipping window; and transforming said clipped character box defined in a first coordinate space to a character box defined in a second coordinate space for display on a graphics display system.

Clipping of fixed character strings in a graphics system

Method and apparatus for providing interpolated display characteristic values, such as intensity or Z value, for pels within a polygon to be displayed by a computer graphics display system. A scanning sequence generates pel addresses such that each pel address so generated is contiguous with a previously generated pel address. The parametric value rate of change in both the X and the Y direction is determined, and expressed as an integer value and a remainder quantity. The remainder quantity is used to determine a sequence, driven by pel address changes, by which the integer parametric value increment from pel to pel is incremented or decremented by one in a regular sequence that assures that the error in the computed parametric value for each pel never exceeds 0.5 parametric value units.

Interpolated display characteristic value generator

In graphics display systems the use of matrix concatenation for coordinate transformation, occasionally, will cause an overflow which may represent an out-of-bounds location of a data element. To correct the overflow problem, a number of translation shift factors are introduced for the last row of the matrix which when used to operate on matrix elements, will maintain the elements within the physical boundaries of the graphics base by preventing overflow. Additionally, a method of adjusting the clipping boundaries to increase the precision of coordinate transformations is also described. The methods of the invention may be implemented in microcode in a commercially availably graphics display system such as the IBM 5080 Graphics System.

Method for controlling concatenation of transformation matrices in a

Method and apparatus for filling convex polygons for display in a raster graphics system is described. Starting from the bottom of the polygon, horizontal lines are drawn to fill the polygon as y-value increments. A polygon-fill processor includes two modified Breshenham line generators.

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West Hurley, NY, United States of America

Bob C Liang