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WID support for displaying hardware crosshair cursor

IP.com Disclosure Number: IPCOM000020429D
Original Publication Date: 2003-Nov-20
Included in the Prior Art Database: 2003-Nov-20
Document File: 1 page(s) / 40K

Publishing Venue

IBM

Abstract

Some applications, such as CAD applications, use a crosshair cursor. If a graphic adapter supports a hardware crosshair cursor, applications can either implement the crosshair cursor in software or use the graphic adapter's hardware cursor. If the crosshair cursor is implemented in software, the application has to manage the crosshair cursor by redrawing the frame buffer every time the pointer device is moved. This method degrades performance, while increasing the applications complexity. When an application uses the hardware crosshair cursor, application complexity is reduced and performance is improved since the application does not have to redraw the frame buffer when the pointer device is moved.

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WID support for displaying hardware crosshair cursor

Most hardware crosshair cursors are full screen. If an application wants to display the crosshair cursor in a window and not the full screen, it would have to implement the crosshair cursor in software. Thus, incurring the performance and complexity penalties. A register on the graphic adapter could be used which would specify a region on the screen where the hardware crosshair cursor is visible. The problem is that if a window is moved partially over the region in which the crosshair cursor is to be displayed, the crosshair cursor will be rendered in the window. There needs to be a way that the crosshair cursor is visible only in a particular window, no matter what the shape of the window is. Thus, preventing it from being displayed in other windows when the windows overlap each other.

Assuming the graphics adapter supports Window IDs (WID)s the solution is to add a crosshair hair cursor enable field in the "Window Attribute Table (WAT)". Since each "Window ID (WID)" corresponds to a particular pixel on the screen, the WID planes can be laid out so that each window on the screen corresponds to a different WID. Since the WID is an index into the WAT, the RAMDAC can display or not display the crosshair cursor based on the WAT crosshair enable field. Therefore the hardware crosshair cursor will only be visible in a particular window even when the windows overlap.

This offers more flexibility when displaying the h...