[Coco] hardware scrolling

[Mathieu Bouchard]

Le 2013-12-09 à 10:07:00, Steve a écrit :

> On 12/8/2013 2:55 PM, Mathieu Bouchard wrote:
>> Is there any way to change the size of the left and right borders ? If you 
>> do so for a whole picture by an amount of 0 to 3 pixels wide, you can 
>> combine it with a every-fourth-dot scrolling to make smooth scrolling in 
>> almost all of the picture.
>
> No, you can not change the size of the marge on a CoCo 1/2.  Even it you 
> could, you would jump every 4 or 8 dots when you started the next byte over. 
> To do hardware scrolling the VDG would need to be able to change what bites 
> are used for what dot on the screen.

No, what I mean is that if you want to scroll just one (or 2 or 3) 
pixel(s) right (move pixels left), you could start the scanline one (or 2 
or 3) pixel(s) earlier (if you could). That way, most columns would be 
correctly smooth-scrolled, except that the columns of the first byte that 
you want to make disappear would still be on-screen (because you can only 
make whole bytes disappear). This would be done mod 4, while whole-byte 
scrolling would still happen. It still would have been a lot better 
sticking with only whole-byte scrolling, even though the borders would 
animate in funny ways.

Oh well.


> Like the CoCo, Apple and IBM all used standard Bitmap graphics for their 
> Hi-res Graphic displays because of there ease of design. (Very simple 
> VDG and memory circuit design.)

I was assuming bitmap graphics all along, not font-changing tricks.

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