XOR support for mouse cursors

[Ben Swartzlander]

So perhaps I'm asking the wrong question. What I want is a cursor that 
is able to invert the color of the pixels underneath it. For example, an 
"I" shaped cursor that looks white over a black background and looks 
black over a white background (and stands out suitably from any other 
color background) to use for text editing. This is the kind of cursor 
that Windows has, and I believe that SDL offers the same type of 
cursors. I don't really care how it's implemented, whether a XOR 
operation is used or not. If a patent is the only thing standing in the 
way of implemented color-inverted cursors, then it should be possible to 
copy whatever prior art existed at the time the patent was filed, thus 
avoiding any patent problems.

-Ben Swartzlander



Graeme Gill wrote:
> Ben Swartzlander wrote:
>
>   
>> Didn't Microsoft Windows 3.0 have XOR cursors? How is it possible to 
>> patent something that already existed in a shipping product at the time? 
>>     
>
> The U.S. Patent Office works in mysterious ways ?
>
> Presumably the patent examiner was convinced that something
> was slightly different in the 1994 patent from previous
> related patents. As I understand it, a patent covers
> the claims minus prior art.
>
>   
>> Just so I understand, is it the case that the X.org team has considered 
>> implementing XOR cursors, and opted not to purely out of legal fears? Or 
>> has it never seriously been considered?
>>     
>
> At one stage all the X11 consortium members were threatened by the
> holder of the XOR cursor patent, even though the X11 server didn't
> actually support an XOR cursor itself. A client application was
> the only way of implementing an XOR cursor, simply by using the XOR
> rendering mode (one of the 16 possible modes).
>
> Typically X11 doesn't need to use an XOR cursor, since it supports
> overlay cursors. XOR cursors are usually regarded as a "trick"
> to avoid having to save what's under the cursor, and restore
> it every time the cursor moves.
>
> Graeme Gill.
>
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