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Re: canvas; draw vector then restore overwritten area later

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From Mike Duffy <md_004@videotron.ca>
Newsgroups comp.lang.javascript
Subject Re: canvas; draw vector then restore overwritten area later
Date Wed, 4 Feb 2015 00:58:38 -0500
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On Sun, 1 Feb 2015 20:08:13 +0000, Dr J R Stockton wrote:

> A circle overlaid on a picture may in places not contrast with the
> picture.  If you can XOR the circle with the original picture, you can
> re-XOR the circle to erase it.

This is indeed an elegant solution to the unstated problem of the drawing
colour having poor contrast against the existing contents of the canvas.

But does SVG have a drawing method that can combine the new object with
previously-rendered canvas values? Or does one need to re-compute or
alternatively "read back" the current canvas state within the area of
interest?

-- 
http://pages.videotron.com/duffym/index.htm

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canvas; draw vector then restore overwritten area later catebekensail@yahoo.com - 2015-01-31 11:19 -0800
  Re: canvas; draw vector then restore overwritten area later "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2015-01-31 20:36 +0100
  Re: canvas; draw vector then restore overwritten area later Denis McMahon <denismfmcmahon@gmail.com> - 2015-01-31 20:09 +0000
  Re: canvas; draw vector then restore overwritten area later Dr J R Stockton <reply1500@merlyn.demon.co.uk.invalid> - 2015-02-01 20:08 +0000
    Re: canvas; draw vector then restore overwritten area later Mike Duffy <md_004@videotron.ca> - 2015-02-04 00:58 -0500
      Re: canvas; draw vector then restore overwritten area later Dr J R Stockton <reply1500@merlyn.demon.co.uk.invalid> - 2015-02-05 23:16 +0000
        Re: canvas; draw vector then restore overwritten area later Mike Duffy <md_004@videotron.ca> - 2015-02-05 20:34 -0500
        Re: canvas; draw vector then restore overwritten area later "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2015-02-05 20:32 -0800
          Re: canvas; draw vector then restore overwritten area later Mike Duffy <md_004@videotron.ca> - 2015-02-06 00:28 -0500
  Re: canvas; draw vector then restore overwritten area later "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2015-02-01 18:58 -0800

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