Posted By
Rachy
on 2005-09-03
03:23:59
|  Re: Writing to the borders of the screen
I don't have sample code at hand, but it is easy as soon as you got the idea: by writing into $FF1D you can reschedule the "beam" on the screen. Which means the drawing is going on, while you can change the logical position and thus adjust what is drawn there. So, all you have to do is waiting for the exact rasterline position (border start) then change $FF1D to the same value which is on the top of the screen (it is 2) and also adjust $FF14 (screen matrix address). Then wait until it reaches the real end of the screen and change back to normal value.
This sounds very easy, but there are a few pitfalls (especially in timing and bad lines), which I don't remember exactly, so it is up to you to find out... 
Before you ask: no, FLD is not working like this...
For FLD (flexible line distance) you have to adjust $FF1F, which is holding the internal couter inside a character row.
|
