[Coco] Raster position

[Sandro Mestre]

What I want, Robert, is to paint my sprites with no flicker.

Nice to know the half-fast poke can be used.

Ta.

2013/3/9 Robert Gault <robert.gault at att.net>

> Sandro Mestre wrote:
>
>> Hello, I'm new to this list.
>>
>> I would like to code a game for the Coco1/2. I usually code for the
>> commodore c64 so I am aquainted with the 6502 but I also can code for the
>> motorolas 6800, 6809 and 680000. During the last days I have coded a
>> sprite
>> engine for a computer with a 6809E and it is working great and then I
>> thought that I could code also the game for the Coco/Dragon computers.
>>
>> I need to know if there is a register that I can poll to check the current
>> raster position
>>
>
> There is no register that tracks the current raster position. If you write
> a program in Basic, then Basic keeps track of the current screen position
> but that's not much use to a machine language program.
>
>
>  or if there is another way to know when the VDP starts
>> painting the horizontal borders.
>>
>
> I think you are asking for the size of the blanking pulse but am not sure.
> The size may differ from Coco to Coco but is I think about 70 lines. If
> that is your question and you have a Coco, run some tests. If you don't
> have a Coco, then get some alpha testers to help you.
>
>
>  I am asking this because as many will know
>> if I paint the sprites there(borders) there will be no flickering. Another
>> option I have would be to use double buffering but then this would eat
>> much
>> more memory and that would be perhaps a no go.
>>
>> How safe is it to use the high speed poke on a game? Do coco games use it?
>>
>>
> On most or all versions of the Coco1, using the full fast poke caused a
> loss of video. I'm not sure if that carried over to the Coco2. However,
> there is a half-fast poke which is address dependent for speed and code in
> RAM is fast while code in ROM is slow. Video works in this mode.
> There is no problem with the fast clock rate on the Coco3 which will run
> programs written for the Coco1 or 2 graphics modes.
>
>
>  Thanks
>>
>> Wood
>>
>>
>
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