Graphics display system and method having improved clipping technique
First Claim
1. In a graphics display system of the kind having a refresh raster display device, a line clipping mechanism for clipping line primitives for viewing in a selected rectangular viewport having horizontal and vertical edges parallel to the X and Y axes respectively of the display area of the display device, and a vector-to-raster converter for converting the clipped lines to patterns of dicrete pels in a refresh buffer, the vector-to-raster converter including an incremental line drawing mechanism responsive to line information supplied by the clipping mechanism to draw the line starting at one endpoint and proceeding towards the other, said mechanism being of the kind in which successive incrementally displaced pairs of X,Y disply coordinates are generated by performing one iteration of an interactive computation in respect of each consecutive coordinate unit along a given stepping axis of the coordinate system, the improvement wherein for at least some lines of a kind which have a first endpoint in the viewport and the second endpoint outside the viewport the vector-to-raster converter is arranged to start the line drawing mechanism at the first endpoint and automatically halt the line drawing mechanism, irrespective of the coordinates of the second endpoint, when the currently generated coordinate along the display axis normal to the viewport edge intersected by the line equals the coordinate of the viewport edge along the same axis, whereby the need for the clipping mechanism to calculate the intersection point of the line with the said viewport edge is avoided.
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Abstract
The invention concerns a graphics display system of the kind having a refresh raster display device, a line clipping mechanism for clipping line primitives for viewing in a selected rectangular viewport having horizontal and vertical edges parallel to the X and Y axes respectively of the display area of the display device, and a vector-to-raster converter for converting the clipped lines to patterns of discrete pels in a refresh buffer, the vector-to-raster converter including an incremental line drawing mechanism responsive to line information supplied by the clipping mechanism to draw the line starting at one endpoint and proceeding towards the other. In such a system, for at least some lines of a kind which have a first endpoint in the viewport and the second endpoint outside the viewport, the clipping mechanism is arranged to avoid calculating the intersection point of the line with the viewport edge intersected by the line, and the vector-to-raster converter is arranged to start the line drawing mechanism at the first endpoint and halt the line drawing mechanism when the currently generated coordinate along the display axis normal th the said viewport edge equals the coordinate of the viewport edge along the same axis.
42 Citations
7 Claims
- 1. In a graphics display system of the kind having a refresh raster display device, a line clipping mechanism for clipping line primitives for viewing in a selected rectangular viewport having horizontal and vertical edges parallel to the X and Y axes respectively of the display area of the display device, and a vector-to-raster converter for converting the clipped lines to patterns of dicrete pels in a refresh buffer, the vector-to-raster converter including an incremental line drawing mechanism responsive to line information supplied by the clipping mechanism to draw the line starting at one endpoint and proceeding towards the other, said mechanism being of the kind in which successive incrementally displaced pairs of X,Y disply coordinates are generated by performing one iteration of an interactive computation in respect of each consecutive coordinate unit along a given stepping axis of the coordinate system, the improvement wherein for at least some lines of a kind which have a first endpoint in the viewport and the second endpoint outside the viewport the vector-to-raster converter is arranged to start the line drawing mechanism at the first endpoint and automatically halt the line drawing mechanism, irrespective of the coordinates of the second endpoint, when the currently generated coordinate along the display axis normal to the viewport edge intersected by the line equals the coordinate of the viewport edge along the same axis, whereby the need for the clipping mechanism to calculate the intersection point of the line with the said viewport edge is avoided.
- 5. In a graphics display system of the kind having a refresh raster display device, a line clipping mechanism for clipping line primitives for viewing in a selected rectangular viewport having horizontal and vertical edges parallel to the X and Y axes respectively of the display area of the display device, and a vector-to-raster converter for converting the clipped lines to patterns of discrete pels in a refresh buffer, the vector-to-raster converter including an incremental line drawing mechanism responsive to line information supplied by the clipping mechanism to draw the line starting at one endpoint and proceeding towards the other, said mechanism being of the kind in which successive incrementally displaced pairs of X,Y display coordinates are generated by performing one iteration of an interactive computation in respect of each consecutive coordinate unit along a given stepping axis of the coordinate system, an improved method of drawing a line of a kind which has a first endpoint in the viewport and the second endpoint outside the viewport which comprises causing the vector-to-raster converter to start the line drawing mechanism at the first endpoint and automatically halt the line drawing mechanism, irrespective of the coordinates of the second endpoint, when the current generated coordinate along the display axis normal to the viewport edge intersected by the line equals the coordinate of the viewport edge along the same axis, whereby the need for the clipping mechanism to calculate the intersection point of the line with the said viewport edge is avoided.
Specification