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Forums > C64 Coding > Left/Right Border switching in middle of rasterline
2016-10-22 19:58
Monte Carlos

Registered: Jun 2004
Posts: 263
Left/Right Border switching in middle of rasterline

The last days i experimented a little with bit 3 of $d016. I had the brainfart to broaden the border on the left and keep it normal on the right. Disappointingly, this seems to work only in every non badline. If i try to switch bit 3 of $d016 during a badline i either get both left and right borders equal or i turn off the border completely for the next rasterline. Does somebody have an explanation in terms of internal VIC timing? I also tried modifying the timing with sprites or HSP to be able to write to $d016 in the correct cycle.
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2016-10-25 20:43
Rastah Bar

Registered: Oct 2012
Posts: 154
Quoting Color Bar
Can't you hide it by making the right border broad instead?

I guess that's not very handy for a text scroller.
2016-10-26 10:07
Monte Carlos

Registered: Jun 2004
Posts: 263
Not even in arabic language, because a major bug would appear on the left side independent on scroll direction.
2017-06-04 19:29

Registered: Mar 2005
Posts: 279
Looks like you've done the impossible MonteCarlos! – changed the color in the middle of the char – second row at the very right ;-D)

I guess one could use bitmap mode without badlines to create 39 column wide scroll using VSP?
2017-06-04 20:48
Monte Carlos

Registered: Jun 2004
Posts: 263
Where do you see a split in the middle of a char?
Did you use VICE or real machine?
I'm not aware of that what you want to tell me at the moment.
2017-06-04 20:51

Registered: Mar 2005
Posts: 279
@MC: Haha, in your screenshot! Second row, the very last char. I am not sure what's going on there but it looks like you've split the atom ;-)
2017-06-05 05:10

Registered: Aug 2004
Posts: 807
That's a blue $ff character! The split is between char foreground and $d021
2017-06-05 11:11

Registered: Apr 2002
Posts: 4255
the latest shape demo uses sprites to achieve a 41 char wide screen for 40 column scroll.
2017-06-05 14:56

Registered: Mar 2005
Posts: 279
Right Oswald – well spotted!

@CJ: Ah, haha how could I miss that?!
2017-06-05 22:58

Registered: Jan 2005
Posts: 344
isn't that like a normal scroll with sprites to solve the colum -1 thing? Ie. not really splitting anything?
2017-06-06 20:36
Rastah Bar

Registered: Oct 2012
Posts: 154
I noticed that if you change from hires to character screen during a line, that the graphics change 16 pixels / 2 chars later than the colors (for 8565 at least, for 6569 the colors change 2 pixels earlier). In other words, you can see 2 hires characters with the colors of a normal text screen (and vice versa when you change back). I guess if you switch 1 character into the left border, and fill the leftmost column of the hires screen, you can also fake a wider left border. The badlines are again a problem, though, and soft scrolling would be difficult. When the lower 3 bits of $d016 are changed, the position where color changes doesn't move, only the graphics shift.
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