Abstract: A method and apparatus for the management of the data associated with multiple graphics contexts in a computer graphics rendering system. Graphics contexts are built by graphics engines and selectively saved into a context save RAM. Context switches are managed either by modifying a context base pointer to address a new section of the context save RAM, or by writing out a portion of the context save RAM to external storage and reading in a replacement context from external storage. The writing and reading process are managed by a control processor allowing the graphics engines to switch context at the same time. New contexts read from external storage automatically cause regeneration of downstream rasterization parameters.

Abstract: A method is described that gives local control to an application program during the drawing process when a "pickable" primitive intersects the pick window. This control is provided in such a way that the state of graphics workstation remains unaltered. Thus the application program is permitted to make "picking" or visualization decisions at the moment the pick occurs, and then resume execution of the display program wherever desired (typically, at the graphic instruction following the one that caused the pick). This capability enables application programs to provide greater functionality, usability and productivity to their users.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: A method is described for improving the responsiveness and accuracy of a graphics system to user-initiated picking actions. In this method, the visual cueing and pick window positioning components of the graphics system tracking/picking function are temporarily separated at the time the user attempts to pick. By handling these two components of the tracking/picking function independently, both type 1 (failure to pick the desired item) and type 2 (picking an undesired item) errors are prevented. This translates into greater productivity for the graphics system user.

Abstract: 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.

Abstract: 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.