Browse Prior Art Database

Clipping and Windowing With Graphics Display

IP.com Disclosure Number: IPCOM000059614D
Original Publication Date: 1986-Jan-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 2 page(s) / 48K

Publishing Venue

IBM

Related People

Canton, A: AUTHOR [+2]

Abstract

In a multi-color graphics display, hardware is used to provide clipping and windowing. A viewport area is defined by setting bits in an additional all-points-addressable (APA) viewport buffer. This buffer is fed unclipped vectors as only data for a location defined in the buffer will be written. The additional buffer is not required if one color is reserved for a viewport background and only updates to locations which contain that color are allowed. In a display that has an APA display buffer and that can have multiple viewports (windows), it is necessary to ensure that any new data are only written to the correct parts of the display buffer. Conventionally this is performed by passing all vectors through software clipping and viewporting routines that modify the vectors prior to sending them to the display buffer hardware.

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Clipping and Windowing With Graphics Display

In a multi-color graphics display, hardware is used to provide clipping and windowing. A viewport area is defined by setting bits in an additional all-points- addressable (APA) viewport buffer. This buffer is fed unclipped vectors as only data for a location defined in the buffer will be written. The additional buffer is not required if one color is reserved for a viewport background and only updates to locations which contain that color are allowed. In a display that has an APA display buffer and that can have multiple viewports (windows), it is necessary to ensure that any new data are only written to the correct parts of the display buffer. Conventionally this is performed by passing all vectors through software clipping and viewporting routines that modify the vectors prior to sending them to the display buffer hardware. The amount of software may be reduced when the area of the active viewport is defined, by setting bits in an additional APA buffer, as shown in Fig. 1. The update data can then be supplied with unclipped vectors as it will only write data via gating logic into the buffer if the data are for locations defined in this viewport buffer. A disadvantage of this method is that it requires a separate 'Viewport Buffer' although this need not be a dedicated buffer. An alternative implementation that does not require a partially or fully dedicated APA plane as a viewport buffer changes the gating logic to onl...