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Hardware Area Fill for Graphics Display

IP.com Disclosure Number: IPCOM000038607D
Original Publication Date: 1987-Feb-01
Included in the Prior Art Database: 2005-Jan-31
Document File: 2 page(s) / 81K

Publishing Venue

IBM

Related People

Clarke, DA: AUTHOR [+3]

Abstract

In an all-points-addressable (APA) graphics display, a hardware area fill technique for clipped graphics objects is described which allows graphics objects to be area filled by simple hardware at high speed, even when part of the object is clipped off by a screen or viewport boundary. Hardware registers defining X and Y coordinates of screen pels (picture elements) include additional bits to define off-screen space. Logic is provided to prevent drawing in off-screen space and automatically to complete the boundaries before filling. An APA graphics system normally consists of a number of memory arrays (bit planes), each having one addressable location per screen pixel. Most of these planes are usually used to define the colour of the pixels, but often one is reserved for use when drawing area-filled (Image Omitted) objects.

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Hardware Area Fill for Graphics Display

In an all-points-addressable (APA) graphics display, a hardware area fill technique for clipped graphics objects is described which allows graphics objects to be area filled by simple hardware at high speed, even when part of the object is clipped off by a screen or viewport boundary. Hardware registers defining X and Y coordinates of screen pels (picture elements) include additional bits to define off-screen space. Logic is provided to prevent drawing in off-screen space and automatically to complete the boundaries before filling. An APA graphics system normally consists of a number of memory arrays (bit planes), each having one addressable location per screen pixel. Most of these planes are usually used to define the colour of the pixels, but often one is reserved for use when drawing area-filled

(Image Omitted)

objects. The outline of the object to be filled is drawn in this plane and then a rectangular area, containing the outline, is scanned so that the hardware can access the outline plane to identify which pixels lie inside the area (and thus are to be written) and those which lie outside the area (and thus are not to be written). This process is illustrated by Fig. 1. Incorrect filling is caused by loss of the outline due to the action of hardware clipping (the examples in Figs. 2 and 3 illustrating some possible incorrect results). These results are normally avoided by the relatively slow process of software clipping of the outline to screen (or viewport) boundaries and drawing the additional vectors required to complete the outline. This disclosure can be considered in two parts: Firstly, the hardware registers defining the X and Y co-ordinates of the pels are given an extra bit (or bits) in additi...