Re: A89: Re: Re: Survey for the next version of PlusShell
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Re: A89: Re: Re: Survey for the next version of PlusShell
>>
>>At 20:46 1998-11-18 -0500, you wrote:
>>>On the 89 LCD, a sprite must be clipped only when it crosses the top or
>left
>>>side LCD edges.
>>
>>Not really true... a sprite on the top row, with a negative x value
>>(x=-8,y=0) would in that case start writing before the video memory
>>starts... so a special case is needed with such sprites.
>
>That's what I meant: the two special cases are at the top and left side of
>the screen. It's also a good idea to not put the sprite when it is
>completely off the screen in either of the other two directions, although
>that would not really constitute clipping.
Let me revise that: there are actually three cases, the third being that
_both_ coordinates are of negative values. In some clipping routines, this
must be treated as a unique case. (Really; before I implemented that case
in the 89 clipping routine I wrote, it actually crashed the calc when you
tried to move the sprite off both the top and the left edges of the screen
simultaneously) This is very nice because on all other TI calcs there are
eight cases you must implement! (or at least test)
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