| Allegro CL version 8.2 Unrevised from 8.1 to 8.2. 8.1 version |
A paint operation that merges the colors of new content that is being drawn with the current colors of the destination stream's pixels. It does this by doing an exclusive or on the bits of the pixel values. See paint-operation.
An exclusive or is particularly useful for drawing something
temporarily and then erasing it in such a way that the original
drawing remains undisturbed. This can be done by simply drawing the
temporary content twice using po-xor
, where the second draw does the
non-destructive erasing. The rubber-banding functions such as get-line and get-shape-box use po-xor
internally to erase the rubber-banding
line.
The color that results with exclusive or drawing is rather arbitrary, but that is the trade-off for non-destructive erasure.
Copyright (c) 1998-2016, Franz Inc. Oakland, CA., USA. All rights reserved.
This page was not revised from the 8.1 page.
Created 2010.1.21.
| Allegro CL version 8.2 Unrevised from 8.1 to 8.2. 8.1 version |